update_boot.c   [plain text]


/*
 * Copyright (c) 2006-2012 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * FILE: update_boot.c
 * AUTH: Soren Spies (sspies)
 * DATE: 8 June 2006
 * DESC: implement 'kextcache -u' (copying to Apple_Boot partitions)
 *
 */

#include <bless.h>
#include <miscfs/devfs/devfs.h>     // UID_ROOT, GID_WHEEL
#include <fcntl.h>
#include <hfs/hfs_mount.h>          // hfs_mount_args
#include <libgen.h>
#include <mach/mach_error.h>
#include <mach/mach_port.h>         // mach_port_allocate()
#include <servers/bootstrap.h>
#include <sysexits.h>
#include <sys/errno.h>
#include <sys/param.h>
#include <sys/mount.h>
#include <sys/xattr.h>
#include <unistd.h>
#include <apfs/apfs_fsctl.h>

#include <IOKit/kext/kextmanager_types.h>
#include <IOKit/kext/OSKextPrivate.h>
#include <IOKit/kext/kextmanager_types.h>
#include <IOKit/kext/kextmanager_mig.h>
#include <IOKit/IOKitLib.h>
#include <IOKit/IOBSD.h>
#include <IOKit/storage/IOMedia.h>
#include <IOKit/storage/IOPartitionScheme.h>
#include <MediaKit/GPTTypes.h>
#include <bootfiles.h>
#include <CoreFoundation/CoreFoundation.h>
#include <DiskArbitration/DiskArbitration.h>
#include <DiskArbitration/DiskArbitrationPrivate.h>

#include "bootcaches.h"
#include "bootroot_internal.h"      // includes bootroot.h
#include "fork_program.h"
#include "safecalls.h"
#include "kext_tools_util.h"


/******************************************************************************
* File-Globals
******************************************************************************/
static mach_port_t sBRUptLock    = MACH_PORT_NULL;
static mach_port_t sKextdPort    = MACH_PORT_NULL;
static int         sBRUptLockCtr = 0; /* Number of times we've "taken" the volume lock */
static uuid_t      s_vol_uuid;   // XX not threadsafe (10561671)


/******************************************************************************
* Types
******************************************************************************/
enum bootReversions {
    nothingSerious = 0,
    noLabel,                // 1
    copyingOFBooter,        // 2
    copyingEFIBooter,       // 3
    copiedBooters,          // 4
    activatingOFBooter,     // 5
    activatingEFIBooter,    // 6
    activatedBooters,       // 7
};

enum blessIndices {
    kSystemFolderIdx = 0,
    kEFIBooterIdx = 1
    // sBLSetBootInfo() preserves other values
};

const char * bootReversionsStrings[] = {
    NULL,           // unused
    "Label deleted",
    "Unlinking and copying BootX booter",
    "Unlinking and copying EFI booter",
    "Booters copied",
    "Activating BootX",
    "Activating EFI booter",
    "Booters activated"
};


// for Apple_Boot update
struct updatingVol {
    struct bootCaches *caches;          // parsed bootcaches.plist data
    char srcRoot[PATH_MAX];             // src for boot caches as char[]
    uuid_string_t host_uuid;            // initialRoot's UUID
    CFDictionaryRef bpoverrides;        // provided Boot.plist overrides
    CFDictionaryRef csfdeprops;         // CSFDE property cache data (!encr)
    char flatTarget[PATH_MAX];          // indy <helper>/<target>, min-RPS
    OSKextLogSpec warnLogSpec;          // flags for file access warnings
    OSKextLogSpec errLogSpec;           // flags for file access errors
    CFArrayRef boots;                   // BSD Names of Apple_Boot partitions
    DASessionRef dasession;             // diskarb handle
    BRBlessStyle blessSpec;             // support non-default BR..ToDir()
    BRUpdateOpts_t opts;                // "how hard to try" & other flags

    // default to false for the common kextcache -u case
    Boolean doRPS, doMisc, doBooters;   // what needs updating
    Boolean doSanitize, cleanOnceDir;   // how to cleanse each helper
    Boolean customSource, customDest;   // vs. default B!=R setup
    Boolean useOnceDir;                 // copy to com.apple.boot.once
    Boolean useStagingDir;              // use staging directory for copy

    // updated as each Apple_Boot is updated
    int bootIdx;                        // which helper are we updating
    enum bootReversions changestate;    // track changes to roll back
    char bsdname[DEVMAXPATHSIZE];       // bsdname of Apple_Boot
    DADiskRef curBoot;                  // and matching diskarb ref
    char curMount[MNAMELEN];            // path to current boot mountpt
    int curbootfd;                      // Sec: handle to curMount
    char dstdir[PATH_MAX];              // full path to main dest.
    char efidst[PATH_MAX], ofdst[PATH_MAX];
    Boolean onAPM;                      // tweak support based on pmap
    Boolean detectedRecovery;           // seen com.apple.recovery.boot?
};

/******************************************************************************
* Definitions
******************************************************************************/
#define COMPILE_TIME_ASSERT(pred) switch(0){case 0:case pred:;}

// for non-RPS content, including booters
#define OLDEXT ".old"
#define NEWEXT ".new"
#define SCALE_2xEXT "_2x"
#define CONTENTEXT ".contentDetails"
#define kBRRootUUIDFile ".root_uuid"
#define kBRBootOnceDir "/com.apple.boot.once"

// NOTE: These strings must be the same length, or code in ucopyRPS will break!
// There is a compile time assert in the function to this effect.
#define BOOTPLIST_NAME "com.apple.Boot.plist"
#define BOOTPLIST_APM_NAME "com.apple.boot.plist"


/******************************************************************************
* Helpers
******************************************************************************/

// diskarb
static int mountBoot(struct updatingVol *up);
static void unmountBoot(struct updatingVol *up);

// ucopy = unlink & copy
// no race for RPS, so install it first
static int ucopyRPS(struct updatingVol *s);  // nuke/copy to inactive
// the label files (for example) have no fallback, .new is harmless
// XX ucopy"Preboot/Firmware"
static int ucopyMisc(struct updatingVol *s);        // use/overwrite .new names
// booters have fallback paths, but originals might be broken
static int ucopyBooters(struct updatingVol *s);     // nuke/copy booters (inact)
// no label -> hint of indeterminate state (label key in plist?)
static int moveLabels(struct updatingVol *s);       // move aside
static int nukeBRLabels(struct updatingVol *s);     // byebye (all?)
// booters have worst critical:fragile ratio (point of departure)
static int activateBooters(struct updatingVol *s);  // bless new names
// and the RPS data needed for booting
static int activateRPS(struct updatingVol *s);      // leap-frog w/rename()
// finally, the label (indicating a working system via this helper partition)
// XX activate"FirmwarePaths/postboot"
static int activateMisc(struct updatingVol *s);     // rename .new / label
// and now that we're safe
static int nukeFallbacks(struct updatingVol *s);
static int eraseRPS(struct updatingVol *up, char *toErase);
static int addHostVolInfo(struct updatingVol *up, CFURLRef hostVol,
                          CFDictionaryRef bootPrefOverrides, CFURLRef targetStr,
                          CFStringRef pickerLabel);
static CFStringRef copy_kcsuffix(void);

// cleanup routines (RPS is the last step; activateMisc handles label)
static int revertState(struct updatingVol *up);

/* Chain of Trust
 * Our goal is to do anything the bootcaches.plist says, but only to that vol.
 * #1 we only pay attention to root-owned bootcaches.plist files
 * #2 we get an fd to the bootcaches.plist              [trust is here]
// * #3 we validate the bc.plist fd after getting an fd to the volume's root
 * #4 we use stored bsdname for libbless
 * #5 we validate cachefd after the call to bless       [trust -> bsdname]
 * #6 we get curbootfd after each apple_boot mount
 * #7 we validate cachefd after the call                [trust -> curfd]
 * #8 operations take an fd limiting their scope to the mount
 */

// XX should probably rename to all-caps
// seed errno since strlxxx routines do not set it. This will make
// downstream error messages more meaningful (since we're often logging the
// errno value and message).
#define pathcpy(dst, src) do { \
            Boolean useErrno = (errno == 0); \
            if (useErrno)       errno = ENAMETOOLONG; \
            if (strlcpy(dst, src, PATH_MAX) >= PATH_MAX)  goto finish; \
            if (useErrno)       errno = 0; \
    } while(0)
#define pathcat(dst, src) do { \
            Boolean useErrno = (errno == 0); \
            if (useErrno)       errno = ENAMETOOLONG; \
            if (strlcat(dst, src, PATH_MAX) >= PATH_MAX)  goto finish; \
            if (useErrno)       errno = 0; \
    } while(0)
#define makebootpath(path, rpath) do { \
                                    pathcpy(path, up->curMount); \
                                    if (up->useOnceDir) { \
                                        pathcat(path, kBRBootOnceDir); \
                                    } \
                                    if (up->useOnceDir || up->flatTarget[0]) { \
                                        pathcat(path, up->flatTarget); \
                                        /* XX 10561671: basename unsafe */ \
                                        pathcat(path, "/"); \
                                        pathcat(path, basename(rpath)); \
                                    } else { \
                                        pathcat(path, rpath); \
                                    } \
                                } while(0)

// continue versions
#define PATHCPYcont(dst, src) do { \
            if (strlcpy(dst, src, PATH_MAX) >= PATH_MAX)  continue; \
    } while(0)
#define PATHCATcont(dst, src) do { \
            if (strlcat(dst, src, PATH_MAX) >= PATH_MAX)  continue; \
    } while(0)

// break versions
#define PATHCPYbreak(dst, src) do { \
            if (strlcpy(dst, src, PATH_MAX) >= PATH_MAX)  break; \
    } while(0)
#define PATHCATbreak(dst, src) do { \
            if (strlcat(dst, src, PATH_MAX) >= PATH_MAX)  break; \
    } while(0)

#define LOGERRxlate(up, ctx1, ctx2, errval) do {  \
        char *c2cpy = ctx2, ctx[256];  \
        if (ctx2 != NULL) {  \
            snprintf(ctx, sizeof(ctx), "%s: %s", ctx1, c2cpy);  \
        } else {  \
            snprintf(ctx, sizeof(ctx), "%s", ctx1);  \
        }  \
        /* if necessary, modify passed-in argument so errno is returned */  \
        if (errval == -1)       errval = errno;  \
        OSKextLog(/* kext */ NULL, up->errLogSpec,  \
                  "%s: %s", ctx, strerror(errval));  \
    } while(0)


// XX there is overlap between errno values and sysexits
static int
getExitValueFor(errval)
{
    int rval;

    switch (errval) {
        case ELAST + 1:
            rval = EX_SOFTWARE;
            break;
        case EPERM:
            rval = EX_NOPERM;
            break;
        case EAGAIN:
        case ENOLCK:
            rval = EX_OSERR;
            break;
        case -1:
            switch (errno) {
                case EIO:
                    rval = EX_IOERR;
                    break;
                default:
                    rval = EX_OSERR;
                    break;
            }
            break;
        default:
            rval = errval;
    }

    return rval;
}

// TM should no longer add to Apple_Boot partitions (8992773)
#define MOBILEBACKUPS_DIR "/.MobileBackups"
#define MDS_BULWARK "/.metadata_never_index"
#define MDS_DIR "/.Spotlight-V100"
#define FSEVENTS_BULWARK "/.fseventsd/no_log"
#define FSEVENTS_DIR "/.fseventsd"
#define NETBOOT_SHADOW "/.com.apple.NetBootX/shadowfile"
static int
sanitizeBoot(struct updatingVol *up)
{
    int lastErrno = 0;              // best effort
    int fd;
    struct statfs sfs;
    char bloatp[PATH_MAX], blockp[PATH_MAX];
    Boolean blockMissing = true;
    struct stat sb;
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Removing unnecessary bloat.");

    // X if the size similar to a user's data volume, don't scrub
    if ((fstatfs(up->curbootfd, &sfs) == 0) &&
            (sfs.f_blocks * sfs.f_bsize > 1ULL<<32)) {
        goto finish;
    }

    // ensure root ownership of the helper root (opened in mountBoot())
    if ((fstat(up->curbootfd, &sb) == 0) &&
            (sb.st_uid != UID_ROOT || sb.st_gid != GID_WHEEL)) {
        if (fchown(up->curbootfd, UID_ROOT, GID_WHEEL) == -1) {
            lastErrno = errno;
        }
    }

    // Time Machine
    makebootpath(bloatp, MOBILEBACKUPS_DIR);
    if (0 == (stat(bloatp, &sb))) {
        if (sdeepunlink(up->curbootfd, bloatp) == -1) {
            lastErrno = errno;
        }
    } 

    // NetBoot shadow file (see 11535905)
    makebootpath(bloatp, NETBOOT_SHADOW);
    if (0 == (stat(bloatp, &sb))) {
        if (sdeepunlink(up->curbootfd, bloatp) == -1) {
            lastErrno = errno;
        }
    } 

    // Spotlight
    makebootpath(blockp, MDS_BULWARK);
    if (-1 == stat(blockp, &sb) && errno == ENOENT) {
        fd = sopen(up->curbootfd, blockp, O_CREAT, kCacheFileMode);
        if (fd == -1) {
            lastErrno = errno;
        } else {
            close(fd);
        }
    }
    makebootpath(bloatp, MDS_DIR);
    if (0 == (stat(bloatp, &sb))) {
        if (sdeepunlink(up->curbootfd, bloatp) == -1) {
            lastErrno = errno;
        }
    } 

    // FSEvents has its antithesis inside its directory :P
    // we'll assume if no_log is present, that there's no cruft
    makebootpath(bloatp, FSEVENTS_DIR);
    makebootpath(blockp, FSEVENTS_BULWARK);
    if (0 == (stat(bloatp, &sb))) {
        if (-1 == stat(blockp, &sb) && errno == ENOENT) {
            // no bulwark, so nuke the whole thing
            if (sdeepunlink(up->curbootfd, bloatp) == -1) {
                lastErrno = errno;
            }
        } else {
            blockMissing = false;
        }
    } 

    if (blockMissing) {
        // then recreate the directory and the "stay away" file
        if (sdeepmkdir(up->curbootfd, bloatp, kCacheDirMode) == -1) {
            lastErrno = errno;
        }
        fd = sopen(up->curbootfd, blockp, O_CREAT, kCacheFileMode);
        if (fd == -1) {
            lastErrno = errno;
        } else {
            close(fd);
        }
    }

    // no accumulated errors -> success

finish:
    if (lastErrno) {
        OSKextLog(NULL, up->warnLogSpec, "sanitizeBoot(): Warning: %s",
                  strerror(lastErrno));
    }

    return lastErrno;
}


/******************************************************************************
 * checkBootContents
 * Look for missing files in the current Apple_boot (helper) partition.  If
 * anything seems amiss, force an appropriate update.
******************************************************************************/
static void
checkBootContents(struct updatingVol *up)
{
    unsigned i;
    char srcpath[PATH_MAX], dstpath[PATH_MAX];
    struct stat sb;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Looking for missing files.");
   
    // check for non-standard boot bits in this helper partition
    if (notBRDefault(up->curMount, NULL)) {
        up->doRPS = up->doBooters = up->doMisc = true;
        goto finish;
    }
    
    /* looking for missing .VolumeIcon.icns, SystemVersion.plist, 
     * PlatformSupport.plist, .disk_label, etc
     */
    if (!up->doMisc) {
        for (i = 0; i < up->caches->nmisc; i++) {
            pathcpy(srcpath, up->caches->root);
            pathcat(srcpath, up->caches->miscpaths[i].rpath);
            makebootpath(dstpath, up->caches->miscpaths[i].rpath);
        
            // If in the root volume but not the helper, force update
            if (stat(srcpath, &sb) == 0) { 
                // source file exists, now check on Apple_Boot
                if (stat(dstpath, &sb) != 0 && errno == ENOENT) {
                    // missing file, force an update
                    up->doMisc = true;
                    OSKextLog(nil,kOSKextLogFileAccessFlag|kOSKextLogBasicLevel,
                        "Helper partition missing misc files, forcing update");
                    break;
                }
            }         
        }
    }
    
    // now look for boot.efi
    if (!up->doBooters) {
        if (up->caches->efibooter.rpath[0]) {
            makebootpath(dstpath, up->caches->efibooter.rpath);
            if (stat(dstpath, &sb) != 0 && errno == ENOENT) {
                // missing file, force an update
                up->doBooters = true;
                OSKextLog(NULL, kOSKextLogFileAccessFlag|kOSKextLogBasicLevel,
                         "Helper partition missing EFI booter, forcing update");
                goto finish;
            }
        }
        // OF booter deserves love too :)
        if (up->caches->ofbooter.rpath[0]) {
            makebootpath(dstpath, up->caches->ofbooter.rpath);
            if (stat(dstpath, &sb) != 0 && errno == ENOENT) {
                // missing file, force an update
                up->doBooters = true;
                OSKextLog(NULL, kOSKextLogFileAccessFlag|kOSKextLogBasicLevel,
                         "Helper partition missing OF booter, forcing update");
                goto finish;
            }
        }
    }

    // RPS content not checked
    
finish:
    return;
}

/*******************************************************************************
* updateBootHelpers() updates per the passed-in struct updatingVol.
* Sec: must ensure each target is one of the source's Apple_Boot partitions
* Logically, callers provide up->boots,caches but initContext() also
* fills in up->dasession.  Callers must also releaseContext() afterwards.
*
* "expect up to date" -> just move the labels aside
******************************************************************************/
static int
updateBootHelpers(struct updatingVol *up)
{
    int errnum, result = 0;
    struct stat sb;
    CFIndex bootcount, bootupdates = 0;
 
    if (up->curbootfd != -1) {
        close(up->curbootfd);
        up->curbootfd = -1;
    }

    // if the plist has gone stale, punt
    if ((result = fstat(up->caches->cachefd, &sb))) {
        OSKextLog(NULL, up->errLogSpec, "fstat(cachefd): %s", strerror(errno));
        goto finish;
    }

    bootcount = CFArrayGetCount(up->boots);
    for (up->bootIdx = 0; up->bootIdx < bootcount; up->bootIdx++) {
        char path[PATH_MAX];

        up->changestate = nothingSerious;           // init state
        if ((errnum = mountBoot(up))) {             // sets curMount
            result = errnum; goto bootfail;  
        }

        // if directed, do our best to nuke anything that doesn't belong
        if (up->doSanitize) {
            (void)sanitizeBoot(up);
        }
        if (up->cleanOnceDir && 
                strlcpy(path, up->curMount, PATH_MAX) < PATH_MAX &&
                strlcat(path, kBRBootOnceDir, PATH_MAX) < PATH_MAX &&
                0 == stat(path, &sb)) {
            (void)sdeepunlink(up->curbootfd, path);
        }

        // If files are missing, update up.do* to ensure we copy them
        // (implicitly forcing their update in subsequent helpers).
        checkBootContents(up);

        // If breaking default config, mark helper as tainted
        if (up->customSource && !up->customDest) {
            markNotBRDefault(up->curbootfd, up->curMount, NULL, true);
        }

        if (up->doRPS && (result = ucopyRPS(up))) {
            goto bootfail;          // new RPS content inactive
        }
        if (up->doMisc) {
            (void)ucopyMisc(up);    // -> .new files
        }
        
        // get the label out of the way (should be optional?)
        // expectUpToDate => early boot -> harder to generate label?
        if (up->opts & kBRUExpectUpToDate) {
            if ((result = moveLabels(up))) {
                goto bootfail;
            }
        } else {
            if ((result = nukeBRLabels(up))) {
                goto bootfail;
            }
        }

        if (up->doBooters && (result = ucopyBooters(up))) {
            goto bootfail;      // .old still active
        }
        // If we blessed the Recovery OS in ucopyRPS(), there's likely only
        // one RPS dir, the new one, and this activateBooters() is the
        // last step before the final F_FULLFSYNC in activateRPS().
        if (up->doBooters && (result = activateBooters(up))) { // committed
            goto bootfail;
        }

        // 10.x.n+1 booters remain compatible 10.x.n kernels?? (power outage!)
        if (up->doRPS && (result = activateRPS(up))) {         // complete
            goto bootfail;
        }
        if ((result = activateMisc(up))) {
            goto bootfail;      // reverts label
        }

        // if restoring the default configuration, remove any taint
        if (!up->customSource && !up->customDest) {
            markNotBRDefault(up->curbootfd, up->curMount, NULL, false);
        }

        up->changestate = nothingSerious;
        bootupdates++;      // loop success
        // -U -> updates are a warning
        OSKextLog(NULL,kOSKextLogFileAccessFlag|((up->opts & kBRUExpectUpToDate)
                  ? kOSKextLogWarningLevel : kOSKextLogBasicLevel),
                  "Successfully updated %s%s.", up->bsdname, up->flatTarget);
        
bootfail:
        // clean up this helper only, no hard failures in the loop
        if (up->changestate!=nothingSerious && !(up->opts&kBRUHelpersOptional)){
            OSKextLog(NULL, up->errLogSpec,
                      "Error updating helper partition %s, state %d: %s.",
                      up->bsdname, up->changestate,
                      bootReversionsStrings[up->changestate]);
        }
        // unroll any changes we may have made
        (void)revertState(up);     // smart enough to do nothing
        
        // clean up and unmount (flatTarget -> might not be a helper)
        // X could check for MNT_DONTBROWSE as a hint it's okay to unmount
        if (nukeFallbacks(up)) {
            OSKextLog(NULL, up->errLogSpec, "Warning: %s%s may be untidy.",
                      up->bsdname, up->flatTarget);
        }
        unmountBoot(up);       // smart, handles "when to unmount" policy 
    }

    if (bootupdates != bootcount && !(up->opts&kBRUHelpersOptional)) {
        OSKextLog(NULL, up->errLogSpec, "Failed to update helper partition%s.",
                  bootcount - bootupdates == 1 ? "" : "s");
        // bullet-proofing: make sure there is a generic error
        if (result == 0) {
            // should always be a non-zero result at this point
            result = ELAST + 1;
        }
        goto finish;
    }

finish:
    return result;
}

/******************************************************************************
* entry points to update caches and copy files to helper partitions
* these culminate in BRUpdateBootFiles() and BRCopyBootFiles().
******************************************************************************/
// XX move to bootcaches.[ch]?
/* sBRUptLock is accessible here and could be used to conditionalize
   the setting of ...skiplocks.  This function might be useful to
   kextd, though it would be a significant change in that kextd
   would now be calling the 'rebuild' functions as well as the
   'check' functions (instead of calling kextcache -u).  For example,
   it would preclude multiple stacked kextcache -u processes (good)
   but change the nature of canceling in-progress updates (unknown).
   kextd's memory footprint would likely grow (one way or another).
 
   invalidateKextCache - if TRUE then we mimic 
   "sudo touch /System/Library/Extensions"
*/
// FIXME: eliminate unnecessary 'anyUpdates' parameter.  Callers can
// detect whether caches were rebuilt by checking filesystem timestamps
// with needUpdates().
int
checkRebuildAllCaches(struct bootCaches *caches,
                      int oodLogSpec,
                      Boolean invalidateKextCache,
                      Boolean earlyBootCheckUpdate,
                      Boolean startupKextsOk,
                      Boolean buildImmutableKernel,
                      Boolean *anyUpdates)
{
    int opres, result = ELAST + 1;  // no pathc() [yet]
    struct stat sb;
    Boolean didUpdate = false;
#if DEV_KERNEL_SUPPORT
    char *  suffixPtr           = NULL; // must free
    char *  tmpKernelPath       = NULL; // must free
#endif
    char imk_path[PATH_MAX] = {};

    if (caches == NULL)  goto finish;
    // if the caches data is no longer valid, abort immediately
    if ((opres = fstat(caches->cachefd, &sb))) {
        result = opres; goto finish;
    }

    OSKextLog(NULL, kOSKextLogProgressLevel | kOSKextLogArchiveFlag,
              "Ensuring %s's caches are up to date.", caches->root);

    /* XX Sec (re-review?): can't let an external volume insert a cache
     * - mktmp/mkstmp used to create temp file at destination
     * - final rename must be on whatever volume provided the kexts
     * - if volume is /, then kexts owned by root can be trusted (4623559 fstat)
     * - otherwise, rename from wrong volume will fail
     */

    // We have to rely on the system's kextcache + IOKit.framework to
    // rebuild these caches.  If called on an older system via
    // libBootRoot against newer cache files, the launched kextcache
    // processes are unlikely to know how to update the caches.  Errors
    // should be returned.

    if (buildImmutableKernel) {
        if (!translatePrelinkedToImmutablePath(caches->kext_boot_cache_file->rpath,
                                               imk_path, sizeof(imk_path))) {
            OSKextLog(/* kext */ NULL,
                      kOSKextLogGeneralFlag | kOSKextLogErrorLevel,
                      "Cannot construct immutablekernel path from \"%s\".",
                      caches->kext_boot_cache_file->rpath);
            result = EX_SOFTWARE;
            goto finish;
        }
    }

    // update the various kernel caches
    if (invalidateKextCache ||
        check_kext_boot_cache_file(caches,
                                   caches->kext_boot_cache_file->rpath,
                                   caches->kernelpath, imk_path)) {
        // rebuild the mkext under our lock / lack thereof
        // (-v forwarded via environment variable by kextcache & kextd)
        OSKextLog(nil, oodLogSpec, "rebuilding %s%s",
                  caches->root ? caches->root : "/",
                  caches->kext_boot_cache_file->rpath);
        if ((opres = rebuild_kext_boot_cache_file(caches,
                                                  caches->kext_boot_cache_file->rpath,
                                                  caches->kernelpath,
                                                  startupKextsOk,
                                                  buildImmutableKernel))) {
            OSKextLog(NULL, kOSKextLogErrorLevel | kOSKextLogArchiveFlag,
                      "Error %d rebuilding %s", result,
                      caches->kext_boot_cache_file->rpath);
            result = opres; goto finish;
        } else {
            didUpdate = true;
        }
    } else {
        OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogArchiveFlag,
                  "Primary kext cache does not need update.");
    }
#if DEV_KERNEL_SUPPORT
    if (caches->extraKernelCachePaths) {
        int             i;
        cachedPath *    cp;
        
        tmpKernelPath = malloc(PATH_MAX);
        if (tmpKernelPath) {
            for (i = 0; i < caches->nekcp; i++) {
                cp = &caches->extraKernelCachePaths[i];
                SAFE_FREE_NULL(suffixPtr);
                
                suffixPtr = getPathExtension(cp->rpath);
                if (suffixPtr == NULL)
                    continue;
                if (strlcpy(tmpKernelPath, caches->kernelpath, PATH_MAX) >= PATH_MAX)
                    continue;
                if (strlcat(tmpKernelPath, ".", PATH_MAX) >= PATH_MAX)
                    continue;
                if (strlcat(tmpKernelPath, suffixPtr, PATH_MAX) >= PATH_MAX)
                    continue;
                if (buildImmutableKernel) {
                    if (!translatePrelinkedToImmutablePath(cp->rpath, imk_path, sizeof(imk_path))) {
                        OSKextLog(/* kext */ NULL,
                                  kOSKextLogGeneralFlag | kOSKextLogErrorLevel,
                                  "Cannot construct immutablekernel path from \"%s\".",
                                  cp->rpath);
                        result = EX_SOFTWARE;
                        goto finish;
                    }
                }
                if (invalidateKextCache ||
                    check_kext_boot_cache_file(caches, cp->rpath, tmpKernelPath, imk_path)) {
                    if ((opres = rebuild_kext_boot_cache_file(caches,
                                                              cp->rpath,
                                                              tmpKernelPath,
                                                              startupKextsOk,
                                                              buildImmutableKernel))){
                        result = opres; goto finish;
                    }
                }
            } // for loop...
        }
    }
    
#endif
    
    // Check/rebuild the CSFDE property cache which goes into the Apple_Boot.
    // It's less critical for booting, but more critical for security.
    if (check_csfde(caches)) {
        OSKextLog(NULL,oodLogSpec,"rebuilding %s",caches->erpropcache->rpath);
        if ((opres = rebuild_csfde_cache(caches))) {
            OSKextLog(NULL, kOSKextLogErrorLevel | kOSKextLogArchiveFlag,
                      "Error %d rebuilding %s", result,
                      caches->erpropcache->rpath);
            result = opres; goto finish;
        } else {
            didUpdate = true;
        }
    } else {
        OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogArchiveFlag,
                  "CSFDE property cache does not need update.");
    }
    
    // check on the (optional) localized resources used by EFI Login
    // Match kextd shutdown policy in 16513211 and don't bother rebuilding
    // EFILoginLocalizations during early boot (probably wouldn't work anyway?).
    if (!earlyBootCheckUpdate && check_loccache(caches)) {
        OSKextLog(NULL,oodLogSpec,"rebuilding %s",caches->efiloccache->rpath);
        if ((result = rebuild_loccache(caches))) {
            OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogArchiveFlag,
                      "Warning: Error rebuilding %s", caches->efiloccache->rpath);
        } else {
            didUpdate = true;
        }
        // efiloccache is not required when copying rpspaths
        // so we can ignore failures to rebuild the cache.
    } else {
        OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogArchiveFlag,
                  "Localized EFI Login resources do not need update.");
    }
    
    // success!
    result = 0;

    // report back if we did any updates
    if (anyUpdates)     *anyUpdates = didUpdate;
    
finish:
#if DEV_KERNEL_SUPPORT
    SAFE_FREE(tmpKernelPath);
    SAFE_FREE(suffixPtr);
#endif
    
    return result;
}


/*****************************************************************************
* initContext() sets up a struct updatingVol for use by other functions
* - volRoot must contain a supported bootcaches.plist
* - volRoot will be locked with kextd
* - if available, diskarb will be configured up->dasession
* - specifiying helperBSDName -> up->boots = [ helperBSDName ]
* releaseContext() should be called when the context is no longer needed.
*****************************************************************************/
#define BOOTCOUNT 1
static int
initContext(struct updatingVol *up, CFURLRef srcVol, CFStringRef helperBSDName,
            BRUpdateOpts_t opts)
{
    int opres, result = ELAST + 1;      // all paths should reset
    const void  *values[BOOTCOUNT] = { helperBSDName };

    // start fresh (all booleans to default false values)
    bzero(up, sizeof(struct updatingVol));
    up->curbootfd = -1;                 // should be -1 or valid descriptor
    
    // establish default options
    up->warnLogSpec = kOSKextLogArchiveFlag | kOSKextLogWarningLevel;
    up->errLogSpec = kOSKextLogArchiveFlag | kOSKextLogErrorLevel;
    up->blessSpec = kBRBlessFSDefault;

    // stash opts for subroutines
    up->opts = opts;

    // takeVolumeForPath() wants a char* ... comes before up->caches = ...
    if (!CFURLGetFileSystemRepresentation(srcVol, /* resolveToBase */ true,
                             (UInt8 *)up->srcRoot,sizeof(up->srcRoot))){
        OSKextLogStringError(NULL);
        result = ENOMEM; goto finish;
    }

    // Theoretically we don't need to lock to read bootcaches.plist, but
    // read[SIC]BootCaches() will create S/L/Caches/bootstamps if missing.
    // -Boot -> don't sync w/kextd
    if ((opts & kBRUEarlyBoot) == 0) {
        if ((opres = takeVolumeForPath(up->srcRoot))) { // lock (logs errors)
            result = opres; goto finish;
        }
    }

    // initializing the context fails if there's no bootcaches.plist
    if (!(up->caches = readBootCaches(up->srcRoot, opts))) {
        result = errno ? errno : ELAST + 1;
        goto finish;
    }

    // attempt to configure a disk arb session
    if ((up->dasession = DASessionCreate(nil))) {
        // mountBoot and unmountBoot will spin the runloop for this DA session
        DASessionScheduleWithRunLoop(up->dasession, CFRunLoopGetCurrent(),
                kCFRunLoopDefaultMode);
    } else {
        OSKextLog(NULL, up->warnLogSpec, "Warning: proceeding w/o DiskArb");
    }

    // if specified, this partition is the one to update
    if (helperBSDName) {
        up->boots = CFArrayCreate(nil,values,BOOTCOUNT,&kCFTypeArrayCallBacks);
    }

    // if specified, use the BR-owned staging directory.
    up->useStagingDir = (opts & kBRUseStagingDir) != 0;

    result = 0;

finish:
    return result;
}

static void
releaseContext(struct updatingVol *up, int status)
{
    // unmountBoot() not always called
    if (up->curBoot)            CFRelease(up->curBoot);
    if (up->curbootfd != -1) {
        close(up->curbootfd);
        up->curbootfd = -1;
    }

    if (up->dasession) {
        DASessionUnscheduleFromRunLoop(up->dasession, CFRunLoopGetCurrent(),
                kCFRunLoopDefaultMode);
        CFRelease(up->dasession);
        up->dasession = NULL;
    }

    if (up->boots)          CFRelease(up->boots);
    if (up->csfdeprops)     CFRelease(up->csfdeprops);
    if (up->bpoverrides)    CFRelease(up->bpoverrides);
    if (up->caches)         destroyCaches(up->caches);

    // unlock
    putVolumeForPath(up->srcRoot, status);
}

static void
addDictOverride(const void *key, const void *value, void *ctx)
{
    CFMutableDictionaryRef tgtDict = (CFMutableDictionaryRef)ctx;

    // AddValue is "add if absent;" we implement override by removing
    if (CFDictionaryContainsKey(tgtDict, key))
        CFDictionaryRemoveValue(tgtDict, key);

    CFDictionaryAddValue(tgtDict, key, value);
}

static CFDataRef
createBootPrefData(struct updatingVol *up, uuid_string_t root_uuid,
                   CFDictionaryRef bootPrefOverrides)
{
    CFDataRef rval = NULL;
    char srcpath[PATH_MAX];
    int fd = -1;
    void *buf = NULL;
    CFDataRef data = NULL;
    CFMutableDictionaryRef pldict = NULL;
    CFStringRef UUIDStr = NULL;
    CFStringRef kernPathStr = NULL;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "creating com.apple.Boot.plist data with UUID %s.",
              root_uuid);

    // suck in any existing plist
    do {
        struct stat sb;
        PATHCPYcont(srcpath, up->caches->root);
        PATHCATcont(srcpath, up->caches->bootconfig->rpath);
        if (-1 == (fd=sopen(up->caches->cachefd,srcpath,O_RDONLY,0)))
            break;
        if (fstat(fd, &sb))                                 break;
        if (sb.st_size > UINT_MAX || sb.st_size > LONG_MAX) break;
        if (!(buf = malloc((size_t)sb.st_size)))            break;
        if (read(fd, buf, (size_t)sb.st_size) != sb.st_size)break;
        if (!(data = CFDataCreate(nil, buf, (long)sb.st_size)))
            break;

        // make mutable dictionary from file data
        pldict =(CFMutableDictionaryRef)
            CFPropertyListCreateWithData(nil,
                                         data,
                                         kCFPropertyListMutableContainers,
                                         NULL,
                                         NULL/*err*/);
    } while(0);

    errno = 0;

    // if we got a dictionary, just grab the file mode
    if (!pldict || CFGetTypeID(pldict)!=CFDictionaryGetTypeID()) {
        // otherwise, create a dictionary
        if (pldict)      CFRelease(pldict);     // e.g. if it was a non-dict
        pldict = CFDictionaryCreateMutable(nil, 1,
                                        &kCFTypeDictionaryKeyCallBacks,
                                        &kCFTypeDictionaryValueCallBacks);
        if (!pldict)    goto finish;
    }

    // make a CFStr out of the UUID and insert
    errno = 0;
    UUIDStr = CFStringCreateWithCString(nil,root_uuid,kCFStringEncodingASCII);
    if (!UUIDStr)   goto finish;
    CFDictionarySetValue(pldict, CFSTR(kRootUUIDKey), UUIDStr);
    if (!CFEqual(CFDictionaryGetValue(pldict,CFSTR(kRootUUIDKey)), UUIDStr))
        goto finish;

    // if necessary, tell the booter to load <flatTarget>/prelinkedkernel
    if (up->flatTarget[0] || up->useOnceDir) {
        char kpath[PATH_MAX] = "";
        /* XX 10561671: basename() unsafe */
        if (up->useOnceDir) {
            pathcat(kpath, kBRBootOnceDir);
        }
        pathcat(kpath, up->flatTarget);
        pathcat(kpath, "/");
        pathcat(kpath, basename(up->caches->kext_boot_cache_file->rpath));
        kernPathStr = CFStringCreateWithFileSystemRepresentation(nil, kpath);
        if (!kernPathStr)   goto finish;
        CFDictionarySetValue(pldict, CFSTR(kKernelCacheKey), kernPathStr);
    }

    // add any additional override values
    if (bootPrefOverrides) {
        CFDictionaryApplyFunction(bootPrefOverrides,addDictOverride,pldict);
    }

    rval = CFPropertyListCreateData(nil, pldict, kCFPropertyListXMLFormat_v1_0,
                                    0 /* !opts */, NULL);

finish:
    if (kernPathStr)    CFRelease(kernPathStr);
    if (UUIDStr)        CFRelease(UUIDStr);
    if (pldict)         CFRelease(pldict);
    if (data)           CFRelease(data);

    if (buf)        free(buf);
    if (fd != -1)   close(fd);

    return rval;
}


/*
 * needUpdatesNoUUID() checks the top-level bootstamps directory.
 * 12369781: allow asr to change the fsys UUID w/o first boot rebooting
 *
 */
static bool
noUUIDStampsUpToDate(CFURLRef volURL)
{
    Boolean altStampsUTD = false;
    char volRoot[PATH_MAX];
    struct bootCaches *caches = NULL;

    if (!CFURLGetFileSystemRepresentation(volURL, /* resolve */ true,
                                          (UInt8*)volRoot, sizeof(volRoot))) {
        OSKextLogStringError(NULL);
        goto finish;
    }

    // "any stamps" option changes the embedded bootstamp paths
    caches = readBootCaches(volRoot, kBRAnyBootStamps);
    if (!caches) {
        goto finish;
    }

    // needUpdates() has already been called once with higher verbosity
    altStampsUTD = (false == needUpdates(caches, kBROptsNone,
                                         NULL, NULL, NULL,
                               kOSKextLogGeneralFlag | kOSKextLogDetailLevel));

finish:
    if (caches)     destroyCaches(caches);

    return altStampsUTD;
}

/******************************************************************************
* checkUpdateCachesAndBoots() returns
* - success (EX_OK / 0) if nothing needs updating
* - success if updates were successfully made (and expectUTD = false)
* - EX_OSFILE if updates were unexpectedly needed and successfully made
******************************************************************************/
// keeping these active for reliability testing of live builds
#define BRDBG_OOD_HANG_BOOT_F "/var/db/.BRHangBootOnOODCaches"
#define BRDBG_HANG_MSG PRODUCT_NAME ": " BRDBG_OOD_HANG_BOOT_F \
                    " -> hanging on out of date caches"
#define BRDBG_CONS_MSG "[via /dev/console] " BRDBG_HANG_MSG "\n"
int
checkUpdateCachesAndBoots(CFURLRef volumeURL, BRUpdateOpts_t opts)
{
    int opres, result = ELAST + 1;          // try to always set on error
    OSKextLogSpec oodLogSpec = kOSKextLogGeneralFlag | kOSKextLogBasicLevel;
    Boolean earlyBootCheckUpdate;           // derived from opts
    Boolean anyCacheUpdates = false;        // so -U can reboot w/o helpers
    Boolean doAny = false, cachesUpToDate = false, doMisc;
    Boolean loggedOOD = false;
    struct updatingVol up = { /*NULL...*/ };
    up.curbootfd = -1;

    // arguably this (and BRCopyBootFilesToDir()) could just check '-Boot'
    earlyBootCheckUpdate = ((opts & kBRUExpectUpToDate) && (opts & kBRUEarlyBoot));
    
    // try to configure 'up'; treat missing data per opts
    if ((opres = initContext(&up, volumeURL, NULL, opts))) {
        char *bcmsg = NULL;
        CFArrayRef helpers;
        switch (opres) {        // describe known problems
            case ENOENT: bcmsg = "no " kBootCachesPath; break;
            case EFTYPE: bcmsg = "unrecognized " kBootCachesPath; break;
            default:     break;
        }
        if ((opts & kBRUForceUpdateHelpers) &&
                (helpers = BRCopyActiveBootPartitions(volumeURL))) {
            // helper partitions + -f => we require bootcaches.plist
            OSKextLog(NULL,up.errLogSpec,"%s: %s; aborting",up.srcRoot,bcmsg);
            CFRelease(helpers);
            result = opres; goto finish;
        } else if (bcmsg) {
            // politely pass on known limitations
            OSKextLog(NULL, oodLogSpec, "%s: %s; skipping",up.srcRoot,bcmsg);
            result = 0; goto finish;
        } else {
            // unknown error; fail
            OSKextLog(NULL, up.errLogSpec, "%s: error %d reading "
                      kBootCachesPath, up.srcRoot, opres);
            result = opres; goto finish;
        }
    }

    // -U logs what is out of date at a a more urgent level than -u
    if (opts & kBRUExpectUpToDate) {
        oodLogSpec = up.errLogSpec;
    }

    // Do some real work updating caches *in* the source volume.
    // earlyBootCheckUpdate restricts which caches are rebuilt.
    if ((opres = checkRebuildAllCaches(up.caches, oodLogSpec,
                                       (opts & kBRUInvalidateKextcache),
                                       earlyBootCheckUpdate,
                                       true /* -all-loaded okay */,
                                       (opts & kBRUImmutableKernel),
                                       &anyCacheUpdates))) {
        result = opres; goto finish;    // error logged by function
    }

    // record partial success
    cachesUpToDate = true;
    
    // 9455881: If requested, only update the caches
    if (opts & kBRUCachesOnly) {
        goto doneUpdatingHelpers;
    }

    if (!hasBootRootBoots(up.caches, &up.boots, NULL, &up.onAPM)) {
        OSKextLog(NULL, kOSKextLogBasicLevel | kOSKextLogFileAccessFlag,
              "%s: no supported helper partitions to update.", up.srcRoot);
        goto doneUpdatingHelpers;   // no boots -> nothing more to do
    }

    /* --- updating a Boot!=Root volume --- */

    // these are helper (not OS) partitions & should be clean
    up.doSanitize = true;

    // figure out what needs updating
    // needUpdates() also populates the timestamp values used by updateStamps()
    if (needUpdates(up.caches, opts, &up.doRPS, &up.doBooters, &doMisc,
                    oodLogSpec)) {
        // if we don't do updates, at least emit a reassuring message
        loggedOOD = true;
    }

    // calculate doAny; misc files aren't worth a reboot in the -U -Boot case
    if (!earlyBootCheckUpdate) {
        up.doMisc = doMisc;
    } 
    doAny = up.doRPS || up.doBooters || up.doMisc;

    // for -U -Boot, reset doAny if the non-UUID paths are up to date
    if (doAny && earlyBootCheckUpdate && noUUIDStampsUpToDate(volumeURL)) {
        doAny = false;
    }

#ifdef BRDBG_OOD_HANG_BOOT_F
    // check to see if out of date at early boot should cause a hang
    if (doAny && earlyBootCheckUpdate) {
        struct stat sb;
        int consfd = open(_PATH_CONSOLE, O_WRONLY|O_APPEND);
        while (stat(BRDBG_OOD_HANG_BOOT_F, &sb) == 0) {
            OSKextLog(NULL, up.errLogSpec, BRDBG_HANG_MSG);
            if (consfd > -1)
                write(consfd, BRDBG_CONS_MSG, sizeof(BRDBG_CONS_MSG)-1);
            sleep(30);
        }
    }
#endif  // BRDBG_OOD_HANG_BOOT_F

    // force ignores needUpdates() and does extra helper cleanup
    // (note: -Installer -> force, non-default cleanOnce preserves ANI)
    if (opts & kBRUForceUpdateHelpers) {
        up.doRPS = up.doBooters = up.doMisc = true;
        up.cleanOnceDir = true;
    } else if (!doAny) {
        // LogLevelBasic is only emitted with -v and above
        // 'Warning' level clarifies previous "not cached" messages
        OSKextLogSpec utdlogSpec = kOSKextLogFileAccessFlag;
        if (loggedOOD) {
            utdlogSpec |= kOSKextLogWarningLevel;
        } else {
            utdlogSpec |= kOSKextLogBasicLevel;
        }
        OSKextLog(NULL, utdlogSpec, "%s: helper partitions %s up to date.",
                  up.srcRoot,
                  (loggedOOD|earlyBootCheckUpdate) ? "sufficiently":"appear");
        goto doneUpdatingHelpers;
    }

    // configure hostVol-based UUIDs, etc
    if ((opres = addHostVolInfo(&up, volumeURL, NULL, NULL, NULL))) {
        OSKextLog(NULL, kOSKextLogErrorLevel | kOSKextLogFileAccessFlag,
                  "%s: error %d extracting volume info.", up.srcRoot, opres);
        result = opres; goto finish;
    }

    // Update = root from volume containing caches; fill in csfdeprops
    strlcpy(up.host_uuid, up.caches->fsys_uuid, sizeof(up.host_uuid));
    if (up.caches->csfde_uuid) {
        opres = copyCSFDEInfo(up.caches->csfde_uuid, &up.csfdeprops, NULL);
        if (opres) {
            result = opres; goto finish;    // error logged by function
        }
    }

    // request actual helper updates
    if ((opres = updateBootHelpers(&up))) {
        // if we hit ENOSPC for the current root volume, try a smaller cache
        if (opres == ENOSPC && strcmp(up.caches->root, "/") == 0) {
            OSKextLog(NULL, kOSKextLogWarningLevel,
                      "Out of space in helper for '/', trying w/o -all-loaded");
            if ((opres = checkRebuildAllCaches(up.caches, oodLogSpec,
                                               true /* invalidate cache */,
                                               earlyBootCheckUpdate,
                                               false /* no -all-loaded */,
                                               (opts & kBRUImmutableKernel),
                                               &anyCacheUpdates))) {
                result = opres; goto finish;    // error logged by function
            }
            // and try updating helpers again
            opres = updateBootHelpers(&up);
        }
        if (opres) {
            result = opres; goto finish;        // error logged by function
        }
    }

    if ((opres = updateStamps(up.caches, kBCStampsApplyTimes))) {
        OSKextLog(NULL, kOSKextLogErrorLevel | kOSKextLogFileAccessFlag,
                  "%s: could not update bootstamps.", up.srcRoot);
        result = opres; goto finish;
    }

doneUpdatingHelpers:
    // success
    result = 0;

    // kBRUExpectUpToDate is used to differentiate "success: everything clean"
    // from "successfully updated:" the latter exits with EX_OSFILE.  During
    // early boot, there is a restricted set of caches that must be updated.
    // In that case, the exit(EX_OSFILE) informs launchd to force a reboot.
    if ((opts & kBRUExpectUpToDate) && (anyCacheUpdates || doAny)) {
        if (earlyBootCheckUpdate) {
            OSKextLog(NULL, oodLogSpec, "%s updated critical boot files, "
                      "requesting launchd reboot", PRODUCT_NAME);
        }
        result = EX_OSFILE;
    } 

finish:
    if ((up.opts & kBRUHelpersOptional) && cachesUpToDate) {
        // partial success okay
        result = 0;
    }

    // since updateBoots()->exit(), convert common errno values->sysexits(3)
    if (result && result != EX_OSFILE) {
        result = getExitValueFor(result);
    }

    // handles unlock / reporting to kextd
    releaseContext(&up, result);

    // all error paths should log if the functions they call don't

    return result;
}

#define kBRCheckLogSpec (kOSKextLogArchiveFlag | kOSKextLogProgressLevel)
OSStatus
BRUpdateBootFiles(CFURLRef volURL, Boolean force)
{
    if (!volURL)
        return EINVAL;

    return checkUpdateCachesAndBoots(volURL, force?kBRUForceUpdateHelpers:0);
}


/* error handling style in this function is an experiment to find a
   1. correct (doesn't miss errors)
   2. robust (doesn't fall over on correctness if not followed)
   3. accurate (returns detailed error values)
   4. readable (can figure out what's going on)
   5. concise (can we achieve #1-3 w/o using both 'errnum' and 'result'?)
   style for handling errors.
*/
static int
addHostVolInfo(struct updatingVol *up, CFURLRef hostVol,
               CFDictionaryRef bootPrefOverrides, CFURLRef targetStr,
               CFStringRef pickerLabel)
{
    OSStatus result = EOVERFLOW;    // ! only set AFTER error detected !
    OSStatus errnum;                // temp var for collecting error values
    uuid_t host_uuidbytes;
    CFStringRef csUUIDStr = NULL;
    char hostroot[PATH_MAX];

    up->flatTarget[0] = '\0';

    // extract any caller-specified target directory
    if (targetStr && up->useStagingDir) {
        // A destination path was provided with the useStagingDir flag.
        // Since the staging directory has a fixed path,
        // this is an invalid set of options.
        result = EINVAL; goto finish;
    }

    if (targetStr) {
        char targetdir[PATH_MAX] = "", *slash;
        if (!CFURLGetFileSystemRepresentation(targetStr, true /*resolve*/,
                                              (UInt8*)targetdir, PATH_MAX)) {
            result = EINVAL; goto finish;
        }
        // target dir must not be '/'
        slash = targetdir;
        while (*slash == '/')       slash++;
        if (*slash == '\0') {
            result = EINVAL; goto finish;
        }
        if (targetdir[0] != '/') {    // did caller provide a '/'?
            pathcat(up->flatTarget, "/");
        }
        pathcat(up->flatTarget, targetdir);
    }

    // get UUIDs
    if (!CFURLGetFileSystemRepresentation(hostVol, true /*resolve base*/,
            (UInt8*)hostroot, PATH_MAX)) {
        result = ENOMEM; goto finish;
    }
    if ((errnum=copyVolumeInfo(hostroot,&host_uuidbytes,&csUUIDStr,NULL,NULL))){
        result = errnum; goto finish;
    }
    uuid_unparse_upper(host_uuidbytes, up->host_uuid);

    // stash overrides for writeBootPrefData(), set up any CSFDE cache
    up->bpoverrides = bootPrefOverrides;
    if (up->bpoverrides) {
        CFRetain(up->bpoverrides);  // balances releaseContext()
    }
    if (csUUIDStr) {
        if ((errnum = copyCSFDEInfo(csUUIDStr, &up->csfdeprops, NULL))) {
            result = errnum; goto finish;
        }
    }

    if (pickerLabel) {
        if (!CFStringGetFileSystemRepresentation(pickerLabel, 
                                          up->caches->defLabel, PATH_MAX)) {
            result = EINVAL; goto finish;
        }
    }

    result = 0;
    
finish:    
    if (csUUIDStr)      CFRelease(csUUIDStr);

    return result;
}


/******************************************************************************
* copy boot files from source volume to destination partition
* - makes sure caches are up to date
* - copies regardless of bootstamps
* - updates bootstamps if default content -> likely default location
* - w/custom content->default location, marks root and helpers as such
* see bootroot.h for more details
******************************************************************************/
/*
   BRCopyBootFilesToDir() uses circa OS X 10.10 development
   0) force an update like kextcache -u -f (which doesn't use this function)
      B!=R already set up: default content -> default location
   1a) switch a volume to Boot!=Root: 'diskutil cs convert', etc
   1b) brtest copyfiles -anyboot to populate a disk image's Apple_Boot
       setting up B!=R: future default content -> future default location
   2) InstallAssistant (Install OS X.app) [boots until complete, canceled]
      B!=R set up: BaseSystem.dmg (custom) content -> default location
   3) AppleNetInstall [just boot it once]
      B!=R set up: custom content -> custom location

   While not in production use today, brtest allows
   - copy one B!=R's content to another volume's helper (no CSFDE support)
     manual override: non-default content to the default location

   A libBootRoot client could also specify
   - copy to the default location, FS-bless *and* boot once
     potentially custom content -> default location
*/

OSStatus
BRCopyBootFilesToDir(CFURLRef srcVol,
                     CFURLRef initialRoot,
                     CFDictionaryRef bootPrefOverrides,
                     CFStringRef targetBSDName,
                     CFURLRef targetDir,
                     BRBlessStyle blessSpec,
                     CFStringRef pickerLabel,
                     BRUpdateOpts_t opts)
{
    OSStatus            result = ELAST + 1;     // generic = safest
    OSStatus            errnum;
    CFArrayRef          helpers;
    CFStringRef         firstHelper;
    Boolean             doUpdateStamps = false;
    struct updatingVol  up = { /* NULL, ... */ };
    up.curbootfd = -1;

    // defend libBootRoot entry point
    if (!srcVol || !initialRoot || !targetBSDName) {
        result = EINVAL; goto finish;
    }

    // configure a single-helper context
    errnum = initContext(&up, srcVol, targetBSDName, opts);
    if (errnum) {
        result = errnum; goto finish;
    }

    // Detect non-default destination or source
    up.blessSpec = blessSpec;
    up.useOnceDir = ((blessSpec & kBRBlessOnce) &&
                     (blessSpec & kBRBlessFSDefault) == 0) || (up.useStagingDir);
    if (up.useOnceDir || targetDir) {
        // A) a custom destination won't interact w/default
        up.customDest = true;
    } else if (CFEqual(srcVol, initialRoot) == false) {
        // B) targetBSD can't belong to both, so the content won't be default
        up.customSource = true;
    } else if ((helpers = BRCopyActiveBootPartitions(initialRoot))) {
        if ((CFArrayGetCount(helpers)) != 1 ||
                (firstHelper = CFArrayGetValueAtIndex(helpers, 0)) == NULL ||
                CFEqual(targetBSDName, firstHelper) == false) {
        //    C) the only volume is B!=R, but targetBSD is not its only helper
            up.customSource = true;
        } else {
            // looks like default, already-configured Boot!=Root
            doUpdateStamps = true;
        }
        CFRelease(helpers);
    } else {
        // assume default Boot!=Root to be
        doUpdateStamps = true;
    }

    // kBRAnyBootStamps forces a bootstamps update
    if (opts & kBRAnyBootStamps) {
        doUpdateStamps = true;
    }
    up.doSanitize = doUpdateStamps;

    // Make sure all caches are up to date on the source
    // (undefined if OOD & system's kext management/EFILogin can't rebuild)
    errnum = checkRebuildAllCaches(up.caches, kBRCheckLogSpec,
                                   (opts & kBRUInvalidateKextcache),
                                   (opts & kBRUExpectUpToDate) && (opts & kBRUEarlyBoot),
                                   true, /* -all-loaded okay */
                                   false, /* don't rebuild immutable kernel */
                                   NULL);
    if (errnum) {
        result = errnum; goto finish;
    }

    // if writing bootstamps, gather timestamp data to apply on success
    if (doUpdateStamps) {
        (void)needUpdates(up.caches, kBROptsNone, NULL, NULL, NULL,
                          kOSKextLogGeneralFlag | kOSKextLogProgressLevel);
    }

    // configure options shared with checkUpdate...()
    errnum = addHostVolInfo(&up, initialRoot, bootPrefOverrides,
                            targetDir, pickerLabel);
    if (errnum) {
        result = errnum; goto finish;
    }

    // BRCopyBootFiles() always copies everything fresh
    up.doRPS = up.doBooters = up.doMisc = true;
    up.cleanOnceDir = true;
    // Since cleanOnceDir is true, we will also clean up any old stagingDirs.
    
    // And finally, update!
    if ((errnum = updateBootHelpers(&up))) {
        result = errnum; goto finish;
    }

    // update bootstamps if establishing a default configuration
    if (doUpdateStamps) {
        if (opts & kBRAnyBootStamps) {
            // if writing top-level bootstamps, attempt start fresh
            char cachedir[PATH_MAX];
            pathcpy(cachedir, up.caches->root);
            pathcat(cachedir, kTSCacheDir);
            (void)sdeepunlink(up.caches->cachefd, cachedir);
        }
        errnum = updateStamps(up.caches, kBCStampsApplyTimes);
        if (errnum) {
            result = errnum; goto finish;
        }
    }

    // Note any pollution of a default destination from a non-default source.
    if (up.customSource && !up.customDest) {
        (void)taintDefaultStamps(targetBSDName);       // logs warnings
        // (if we failed, it would be up to the client to un-do?)
    }

    // success
    result = 0;

finish:
    releaseContext(&up, result);

    return result;
}

OSStatus
BRCopyBootFiles(CFURLRef srcVol,
                CFURLRef initialRoot,
                CFStringRef helperBSDName,
                CFDictionaryRef bootPrefOverrides)
{
    return BRCopyBootFilesToDir(srcVol, initialRoot, bootPrefOverrides,
                                helperBSDName, NULL /*helperDir*/,
                                kBRBlessFSDefault, NULL /*pickerLabel*/,
                                kBROptsNone);
}

/******************************************************************************
* FindRPSDir plays rock, paper scissors to identify the location of
* the latest complete copy of the files the booter needs.
******************************************************************************/
static int
FindRPSDir(struct updatingVol *up, char prev[PATH_MAX], char current[PATH_MAX],
           char next[PATH_MAX])
{
     char rpath[PATH_MAX], ppath[PATH_MAX], spath[PATH_MAX];   
/*
 * FindRPSDir looks for a "rock," "paper," or "scissors" directory
 * - handle all permutations: 3 dirs, any 2 dirs, any 1 dir
 */
// static EFI_STATUS
// FindRPSDir(EFI_FILE_HANDLE BootDir, EFI_FILE_HANDLE *newBoot)
// 
    int rval = ELAST + 1, status;
    struct stat r, p, s;
    Boolean haveR = false, haveP = false, haveS = false;
    char *prevp = NULL, *curp = NULL, *nextp = NULL;

    // set up full paths with intervening slash
    pathcpy(rpath, up->curMount);
    pathcat(rpath, "/");
    pathcpy(ppath, rpath);
    pathcpy(spath, rpath);

    pathcat(rpath, kBootDirR);
    pathcat(ppath, kBootDirP);
    pathcat(spath, kBootDirS);

    status = stat(rpath, &r);   // easier to let this fail
    haveR = (status == 0);
    status = stat(ppath, &p);
    haveP = (status == 0);
    status = stat(spath, &s);
    haveS = (status == 0);

    if (haveR && haveP && haveS) {    // NComb(3,3) = 1
        OSKextLog(NULL, up->warnLogSpec,
                  "Warning: all of R,P,S exist: picking 'R'; destroying 'P'.");
        curp = rpath;   nextp = ppath;  prevp = spath;
        if ((rval = eraseRPS(up, nextp)))
            goto finish;
    }   else if (haveR && haveP) {          // NComb(3,2) = 3
        // p wins
        curp = ppath;   nextp = spath;  prevp = rpath;
    } else if (haveR && haveS) {
        // r wins
        curp = rpath;   nextp = ppath;  prevp = spath;
    } else if (haveP && haveS) {
        // s wins
        curp = spath;   nextp = rpath;  prevp = ppath;
    } else if (haveR) {                     // NComb(3,1) = 3
        // r wins by default
        curp = rpath;   nextp = ppath;  prevp = spath;
    } else if (haveP) {
        // p wins by default
        curp = ppath;   nextp = spath;  prevp = rpath;
    } else if (haveS) {
        // s wins by default
        curp = spath;   nextp = rpath;  prevp = ppath;
    } else {                                          // NComb(3,0) = 0
        // we'll start with rock
        curp = rpath;   nextp = ppath;  prevp = spath;
    }

    if (strlcpy(prev, prevp, PATH_MAX) >= PATH_MAX)     goto finish;
    if (strlcpy(current, curp, PATH_MAX) >= PATH_MAX)   goto finish;
    if (strlcpy(next, nextp, PATH_MAX) >= PATH_MAX)     goto finish;

    rval = 0;

finish:
    if (rval) {
        /* can't use errno here since strlcpy and strlcat don't set it */
        OSKextLog(NULL, up->errLogSpec,
                  "%s - strlcpy or cat failed - >= PATH_MAX", __FUNCTION__);
    }

    return rval;
}

/******************************************************************************
* BREraseBootFiles() un-does BRCopyBootFiles()
******************************************************************************/
// helper does wraps BLSetFinderVolumeInfo with schdir()
static int
sBLSetBootInfo(struct updatingVol *up, uint64_t newvinfo[8])
{
    int result, fd = -1, isAPFS = 0;
    result = schdir(up->curbootfd, up->curMount, &fd);
    if (result)         goto finish;

    if (BLIsMountAPFS(NULL, up->curMount, &isAPFS) != 0) {
        result = EINVAL;
        goto finish;
    }

    if (isAPFS) {
        uint64_t    vinfo[2];
        result = BLGetAPFSBlessData(NULL, ".", vinfo);
        if (result)         goto finish;
        vinfo[0] = newvinfo[kEFIBooterIdx];
        vinfo[1] = newvinfo[kSystemFolderIdx];
        result = BLSetAPFSBlessData(NULL, ".", vinfo);
    } else {
        uint32_t    vinfo[8];
        result = BLGetVolumeFinderInfo(NULL, ".", vinfo);
        if (result)         goto finish;
        vinfo[kSystemFolderIdx] = (uint32_t)newvinfo[kSystemFolderIdx];
        vinfo[kEFIBooterIdx] = (uint32_t)newvinfo[kEFIBooterIdx];
        result = BLSetVolumeFinderInfo(NULL, ".", vinfo);
    }

finish:
    if (fd != -1)  
        (void)restoredir(fd);
    return result;
}

// helper attempts to bless the Recovery OS if present
static int
blessRecovery(struct updatingVol *up)
{
    int result;
    char path[PATH_MAX];
    struct stat sb;
    uint64_t vinfo[8] = { 0, };

    // look up pathnames & file IDs
    result = ENAMETOOLONG;

    // recovery dir always lives at the root of the volume
    pathcpy(path, up->curMount);
    pathcat(path, "/" kRecoveryBootDir);
    if (stat(path, &sb) == -1) {
        result = errno;
        goto finish;
    }
    vinfo[kSystemFolderIdx] = (uint32_t)sb.st_ino;

    // append boot.efi
    pathcat(path, "/");
    pathcat(path, basename(up->caches->efibooter.rpath));
    if (stat(path, &sb) == -1) {
        result = errno;
        goto finish;
    }
    vinfo[kEFIBooterIdx] = (uint32_t)sb.st_ino;

    if ((result = sBLSetBootInfo(up, vinfo))) {
        OSKextLog(NULL, up->warnLogSpec,
                 "Warning: found recovery booter but couldn't bless it.");
    }

    // flush everything in this helper partition to disk
    if ((result = fcntl(up->curbootfd, F_FULLFSYNC))) {
        LOGERRxlate(up, "fcntl(helper, F_FULLFSYNC)", NULL, result);
        goto finish;
    }

finish:
    return result;
}

// 17769081 tracks using this more, but ENOENT can't be right for all
#define RECERR(up, opres, warnmsg) do { \
            if (opres == -1 && errno == ENOENT) { \
                opres = 0; \
            } \
            if (opres) { \
                if (warnmsg) { \
                    OSKextLog(NULL, up->warnLogSpec, warnmsg); \
                } \
                if (firstErr == 0) { \
                    OSKextLog(NULL, up->warnLogSpec, "capturing err %d / %d", \
                              opres, errno); \
                    firstErr = opres; \
                    if (firstErr == -1)     firstErrno = errno; \
                } \
            } \
        } while(0)

OSStatus
BREraseBootFiles(CFURLRef srcVolRoot, CFStringRef helperBSDName)
{
    OSStatus result = ELAST + 1;
    int opres, firstErrno, firstErr = 0; 
    char path[PATH_MAX], prevRPS[PATH_MAX], nextRPS[PATH_MAX];
    struct stat sb;
    uint64_t zerowords[8] = { 0, };
    unsigned i;
    struct updatingVol  up = { /* NULL, ... */ }, *upp = &up;
    up.curbootfd = -1;
    
    // defend libBootRoot entry point
    if (!srcVolRoot || !helperBSDName) {
        result = EINVAL; goto finish;
    }

    opres = initContext(&up, srcVolRoot, helperBSDName, kBROptsNone);
    if (opres) {
        result = opres; goto finish;
    }

    if ((opres = mountBoot(&up))) {        // sets curMount
        result = opres; goto finish;
    }

    // generally best effort

    // bless recovery booter if present; else unbless volume
    if ((blessRecovery(&up))) {
        if ((opres = sBLSetBootInfo(&up, zerowords))) {
            firstErr = opres;
            OSKextLog(NULL, up.warnLogSpec,
                      "Warning: couldn't unbless %s", up.curMount);
        }
    }

    // kill label
    opres = nukeBRLabels(&up);
    RECERR(upp, opres,"Warning: trouble nuking (inactive?) Boot!=Root label.");

    // unlink booters
    if (up.caches->ofbooter.rpath[0]) {
        pathcpy(path, up.curMount);
        pathcat(path, up.caches->ofbooter.rpath);
        opres = sunlink(up.curbootfd, path);
        RECERR(upp, opres, "couldn't unlink OF booter" /* remove w/9217695 */);
    }
    if (up.caches->efibooter.rpath[0]) {
        pathcpy(path, up.curMount);
        pathcat(path, up.caches->efibooter.rpath);
        opres = sunlink(up.curbootfd, path);
        RECERR(upp, opres, "couldn't unlink EFI booter" /* NULL w/9217695 */);
    }

    // find & nuke all RPS directories
    opres = FindRPSDir(&up, prevRPS, up.dstdir, nextRPS);
    if (opres == 0) {
        opres = eraseRPS(&up, prevRPS);
        RECERR(upp, opres, "Warning: trouble erasing R.");
        opres = eraseRPS(&up, up.dstdir);
        RECERR(upp, opres, "Warning: trouble erasing P.");
        opres = eraseRPS(&up, nextRPS);
        RECERR(upp, opres, "Warning: trouble erasing S.");
    } else {
        RECERR(upp, opres, "Warning: couldn't find RPS directories.");
    }
        
    for (i=0; i < up.caches->nmisc; i++) {
        char *rpath = up.caches->miscpaths[i].rpath;

        if (strlcpy(path, up.curMount, PATH_MAX) > PATH_MAX)   continue;
        if (strlcat(path, rpath, PATH_MAX) > PATH_MAX)         continue;
        opres = sdeepunlink(up.curbootfd, path);
        RECERR(upp, opres, "error unlinking miscpath" /* NULL w/9217695 */);
    }

    // clean up com.apple.boot.once if it exists
    pathcpy(path, up.curMount);
    pathcat(path, kBRBootOnceDir);
    if (0 == stat(path, &sb)) {
        opres = sdeepunlink(up.curbootfd, path);
        RECERR(upp, opres, "error unlinking" kBRBootOnceDir);
    }

    // no errors above, so firstErr == 0 -> success
    if (firstErr == -1) {
        firstErr = firstErrno;      // recorded by RECERR
    }
    result = firstErr;

finish:
    unmountBoot(&up);
    releaseContext(&up, result);
    
    return result;
}


/******************************************************************************
* revertState() rolls back incomplete changes
******************************************************************************/
static int
revertState(struct updatingVol *up)
{
    int rval = 0;       // optimism to accumulate errors with |=
    char path[PATH_MAX], oldpath[PATH_MAX];
    struct bootCaches *caches = up->caches;
    Boolean doMisc;
    struct stat sb;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Rolling back any incomplete updates.");
        
    switch (up->changestate) {
        // inactive booters are still good
        case activatedBooters:
            // we've blessed the new booters; so let's bless the old ones
            pathcat(up->ofdst, OLDEXT);
            pathcat(up->efidst, OLDEXT);
            // reactivates the old *if* present
            rval |= activateBooters(up);
        case activatingEFIBooter:
    case activatingOFBooter:        // unneeded since 'bless' is one op
        case copiedBooters:
    case copyingEFIBooter:
        if (caches->efibooter.rpath[0]) {
            makebootpath(path, caches->efibooter.rpath);
            pathcpy(oldpath, path);         // old ones are blessed; rename
            pathcat(oldpath, OLDEXT);
            // only unlink current booter if old one present
            if (stat(oldpath, &sb) == 0) {
                (void)sunlink(up->curbootfd, path);
                rval |= srename(up->curbootfd, oldpath, path);
            }
        }

    case copyingOFBooter:
        if (caches->ofbooter.rpath[0]) {
            makebootpath(path, caches->ofbooter.rpath);
            pathcpy(oldpath, path);
            pathcat(oldpath, OLDEXT);
            // only unlink current booter if old one present
            if (stat(oldpath, &sb) == 0) {
                (void)sunlink(up->curbootfd, path);
                rval |= srename(up->curbootfd, oldpath, path);
            }
        }

    // XX
    // case copyingMisc:
    // would clean up the .new turds

        case noLabel:
            // XX hacky (c.f. nukeFallbacks which nukes .disabled label)
            doMisc = up->doMisc;
            up->doMisc = false;
            rval |= activateMisc(up);  // writes new label if !doMisc
            up->doMisc = doMisc;

        case nothingSerious:
            // everything is good
            break;
    }

finish:
    if (rval) {
        OSKextLog(NULL, kOSKextLogErrorLevel,
                  "error rolling back incomplete updates.");
    }

    return rval;
};

/******************************************************************************
* mountBoot digs in for the root, and mounts up the Apple_Boots
* mountpoint -> up->curMount
******************************************************************************/
static int
_mountBootDA(struct updatingVol *up)
{
    int rval = ELAST + 1;
    CFStringRef mountargs[] = { CFSTR("perm"), CFSTR("nobrowse"), NULL };
    DADissenterRef dis = (void*)kCFNull;
    CFDictionaryRef ddesc = NULL;
    CFURLRef volURL;

    if (!(up->curBoot=DADiskCreateFromBSDName(nil,up->dasession,up->bsdname))){
        goto finish;
    }
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Mounting %s...", up->bsdname);

    // DADiskMountWithArgument might call _daDone before it returns (e.g. if it
    // knows your request is impossible ...)
    // _daDone updates our 'dis[senter]'
    DADiskMountWithArguments(up->curBoot, NULL/*mnt*/,kDADiskMountOptionDefault,
                             _daDone, &dis, mountargs);

    // ... so we use kCFNull and check the value before CFRunLoopRun()
    if (dis == (void*)kCFNull) {
        CFRunLoopRun();         // stopped by _daDone (which updates 'dis')
    }
    if (dis) {
        rval = DADissenterGetStatus(dis);
        // only an error if it's not already mounted
        if (rval != kDAReturnBusy) {
            goto finish;
        }
    }

    // get and stash the mountpoint of the boot partition
    if (!(ddesc = DADiskCopyDescription(up->curBoot)))  goto finish;
    volURL = CFDictionaryGetValue(ddesc, kDADiskDescriptionVolumePathKey);
    if (!volURL || CFGetTypeID(volURL) != CFURLGetTypeID())  goto finish;
    if (!CFURLGetFileSystemRepresentation(volURL, true /*resolve base*/,
            (UInt8*)up->curMount, PATH_MAX))        goto finish;

    // success
    rval = 0;

finish:
    if (rval) {
        if (rval != ELAST + 1) {
            if (rval == -1)     rval = errno;
            OSKextLog(NULL, up->errLogSpec,
                "Failed to mount helper (%d/%#x): %s", rval,
                rval & ~(err_local|err_local_diskarbitration), strerror(rval));
        } else {
            OSKextLog(NULL, up->errLogSpec,"Failed to mount helper partition.");
        }
    }

    if (ddesc)      CFRelease(ddesc);
    if (dis && dis != (void*)kCFNull) { // for spurious CFRunLoopRun() return
        CFRelease(dis);
    }

    return rval;
}

/* _mountBootBuiltIn() will mount with mount(2) in /var/run.  Use
 * _findMountedhelper() first to see if it's already mounted. */
// Creating BRMNT_PARENT instead of using _PATH_VARRUN because the latter
// contains a trailing '/' and lacks the /private that mount(2) expects.
#define BRMNT_PARENT "/private/var/run"
#define BRMNT BRMNT_PARENT "/brmnt"
static int
_mountBootBuiltIn(struct updatingVol *up)
{
    int bsderr, rval = ELAST + 1;       // all paths should set rval
    int vrfd = -1;
    int fd = -1;
    struct stat sb;
    char devpath[DEVMAXPATHSIZE];
    struct hfs_mount_args hfsargs;

    // establish parent fd (assume /var/run safe)
    if (((vrfd = open(_PATH_VARRUN, O_RDONLY))) == -1) {
        rval = vrfd; LOGERRxlate(up, _PATH_VARRUN, NULL, rval); goto finish;
    }

    // examine any existing filesystem object at intended mount point 
    // [Can't use sopen() since BRMNT already hosts a mount.]
    fd = open(BRMNT, O_RDONLY);

    // if it exists but isn't a directory, nuke it
    if (fd != -1 && fstat(fd, &sb)==0 && S_ISDIR(sb.st_mode)==false) {
        if ((bsderr = sunlink(vrfd, BRMNT))) {
            rval = bsderr; LOGERRxlate(up, BRMNT, NULL, rval); goto finish;
        }
        // it should be gone now: reset fd, etc
        close(fd);
        fd = open(BRMNT, O_RDONLY);
        if (fd != -1) {
            rval = EEXIST; LOGERRxlate(up, BRMNT, NULL, rval); goto finish;
        }
    }

    // If BRMNT exists, it is a directory; if not, create it.
    if (fd == -1 && errno == ENOENT) {
        if ((bsderr = smkdir(vrfd, BRMNT, kCacheDirMode))) {
            rval = bsderr; LOGERRxlate(up, "mkdir", BRMNT, rval); goto finish;
        }
    }

    // set up args & mount
    bzero(&hfsargs, sizeof(hfsargs));
    // _PATH_DEV contains a trailing '/'
    (void)snprintf(devpath, sizeof(devpath), _PATH_DEV "%s", up->bsdname);
    hfsargs.fspec = devpath;
    if ((bsderr = mount("hfs", BRMNT, MNT_DONTBROWSE, &hfsargs))) {
        rval = bsderr; LOGERRxlate(up, "mount", BRMNT, rval); goto finish;
    }

    // record result in context
    if (strlcpy(up->curMount, BRMNT, MNAMELEN) >= MNAMELEN) {
        rval = EOVERFLOW; LOGERRxlate(up,up->curMount,NULL,rval); goto finish;
    }

    // success
    rval = 0;

finish:
    if (fd != -1)       close(fd);
    if (vrfd != -1)     close(vrfd);

    return rval;
}

// loop copied from kextd_watchvol.c:reconsiderVolumes()
static int
_findMountedHelper(struct updatingVol *up)
{
    int rval = ELAST + 1;
    int nfsys, i;
    int bufsz;
    struct statfs *mounts = NULL;

    // get mount list
    if (-1 == (nfsys = getfsstat(NULL, 0, MNT_NOWAIT))) {
        rval = errno; goto finish;
    }
    bufsz = nfsys * sizeof(struct statfs);
    if (!(mounts = malloc(bufsz))) {
        rval = errno; goto finish;
    }
    if (-1 == getfsstat(mounts, bufsz, MNT_NOWAIT)) {
        rval = errno; goto finish;
    }

    // see whether the filesystem is already mounted somewhere
    for (i = 0; i < nfsys; i++) {
        struct statfs *sfs = &mounts[i];
        if (strlen(sfs->f_mntfromname) < sizeof(_PATH_DEV) ||
                (strcmp(sfs->f_fstypename, "hfs") &&
                strcmp(sfs->f_fstypename, "apfs"))) {
            continue;
        }
        if (0 == strcmp(sfs->f_mntfromname+strlen(_PATH_DEV), up->bsdname)){
            if (strlcpy(up->curMount, sfs->f_mntonname, MNAMELEN)>=MNAMELEN) {
                rval = EOVERFLOW; goto finish;
            }
            // we found it!
            rval = 0;
            goto finish;
        }
    }

    // default = not found (success in loop)
    rval = ENOENT;

finish:
    if (mounts)     free(mounts);

    return rval;
}

static int
mountBoot(struct updatingVol *up)
{
    int errnum, rval = ELAST + 1;
    CFStringRef str;
    struct statfs bsfs;
    uint32_t mntgoal;
    struct stat sb;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Mounting helper partition...");

    // request the Apple_Boot mount
    str = (CFStringRef)CFArrayGetValueAtIndex(up->boots, up->bootIdx);
    if (!str || CFGetTypeID(str) != CFStringGetTypeID()) {
        goto finish;
    }
    if (!CFStringGetFileSystemRepresentation(str,up->bsdname,DEVMAXPATHSIZE)){
        goto finish;
    }
    if (up->dasession) {
        if ((errnum = _mountBootDA(up))) {
            rval = errnum; goto finish;     // error logged by function
        }
    } else if (_findMountedHelper(up) == ENOENT &&
                (errnum = _mountBootBuiltIn(up))) {
            rval = errnum; goto finish;     // error logged by function
    }

    // Sec: get a non-spoofable handle to the current helper (extend trust)
    if (-1 == (up->curbootfd = open(up->curMount, O_RDONLY, 0))) {
        rval = errno; LOGERRxlate(up, up->curMount, NULL, rval); goto finish;
    }
    // if the source volume still exists, we now have fd's for source & dest
    if (fstat(up->caches->cachefd, &sb)) {
        rval = errno; LOGERRxlate(up, "cachefd MIA?", NULL, rval); goto finish;
    }

    // Make sure the mount is read/write and has owners enabled.
    // Because helper partitions should always have owners enabled
    // and because we soft-unmount afterwards, we don't attempt to
    // restore this state.
    if (fstatfs(up->curbootfd, &bsfs)) {
        rval = errno; LOGERRxlate(up, "curboot MIA?", NULL, rval); goto finish;
    }
    mntgoal = bsfs.f_flags;
    mntgoal &= ~(MNT_RDONLY|MNT_IGNORE_OWNERSHIP);
    if ((bsfs.f_flags != mntgoal) && updateMount(up->curMount, mntgoal)) {
        OSKextLog(NULL, up->warnLogSpec,
                  "Warning: couldn't update mount to read/write + owners");
    }

    // we only support 128+ MB Apple_Boot partitions
    if (bsfs.f_blocks * bsfs.f_bsize < (128 * 1<<20)) {
        rval = EFTYPE;
        OSKextLog(NULL, up->errLogSpec, "skipping Apple_Boot helper < 128 MB.");
        goto finish;
    }

    // If not using the default directories, confirm targetDir exists.
    if (!up->useOnceDir && up->flatTarget[0]) {
        char path[PATH_MAX];
        pathcpy(path, up->curMount);
        pathcat(path, up->flatTarget);
        if (stat(path, &sb) != 0) {
            if (errno == ENOENT) {
                rval = ENOENT;
                LOGERRxlate(up, "target directory must exist", path, rval);
                goto finish;
            }
        } else if (!S_ISDIR(sb.st_mode)) {
            rval = ENOTDIR; LOGERRxlate(up, path, NULL, rval); goto finish;
        }
    }

    // success
    rval = 0;

finish:
    if (rval != 0 && (up->curBoot || up->curMount[0])) {
        (void)unmountBoot(up);      // undo anything significant
    }

    return rval;
}

/******************************************************************************
* unmountBoot 
* attempt to unmount; no worries on failure
******************************************************************************/
static void
unmountBoot(struct updatingVol *up)
{
    int errnum = 0;
    DADissenterRef dis = (void*)kCFNull;

    // clean up curbootfd
    if (up->curbootfd != -1) {
        close(up->curbootfd);
        up->curbootfd = -1;
    }

    // specifying a target directory => might not be a helper volume!
    // And if it's a staging directory, the client is responsible for the unmount.
    if (up->flatTarget[0] || up->useStagingDir) return;
    
    if (up->curMount[0]) {
        OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
                  "Unmounting helper partition %s.", up->bsdname);
    }

    // clean up any DiskArb-mounted filesystem
    if (up->curBoot) {
        // _daDone populates 'dis'[senter]
        DADiskUnmount(up->curBoot,kDADiskMountOptionDefault,_daDone,&dis);
        if (dis == (void*)kCFNull) {    // DA.Unmount can call _daDone
            CFRunLoopRun();
        }

        // if that didn't work, just log
        if (dis) {
            OSKextLog(NULL, up->warnLogSpec,
                      "%s didn't unmount, leaving mounted", up->bsdname);
            if (dis != (void*)kCFNull) {
                CFRelease(dis);
            }
        }
        up->curMount[0] = '\0';     // only try to unmount once
        CFRelease(up->curBoot);
        up->curBoot = NULL;
    }

    // unmount anything mounted by _mountBuiltIn()
    if (up->dasession == NULL && up->curMount[0] != '\0') {
        if (unmount(up->curMount, 0)) {
            errnum = errno;
        }
        up->curMount[0] = '\0';     // only try to unmount once
    }

    if (errnum) {
        OSKextLog(NULL, up->errLogSpec,
            "Failed to unmount helper (%d/%#x): %s", errnum,
            errnum & ~(err_local|err_local_diskarbitration), strerror(errnum));
    }
}


/******************************************************************************
* ucopyRPS unlinks old/copies new RPS content w/o activating
* RPS files are considered important -- non-zero file sizes only!
* XX could validate the kernel with Mach-o header
* several intervening helpers including eraseRPS()
******************************************************************************/
static int
writeBootPrefs(struct updatingVol *up, char *dstpath)
{
    int         opres, rval = ELAST + 1;
    CFDataRef   bpdata = NULL;
    char        dstparent[PATH_MAX];
    ssize_t     len;
    int         fd = -1;

    // create data to be written (uses up->useOnceDir from mountBoot)
    bpdata = createBootPrefData(up, up->host_uuid, up->bpoverrides);
    if (!bpdata)    { rval = ENOMEM; goto finish; }

    // recursively create the parent directory       
    if (strlcpy(dstparent,dirname(dstpath),PATH_MAX) >= PATH_MAX) {
        rval = EOVERFLOW; goto finish;
    }
    opres = sdeepmkdir(up->curbootfd, dstparent, kCacheDirMode);
    if (opres) {
        rval = opres; goto finish;
    }

    // sopen adds O_EXCL to O_CREAT
    (void)sunlink(up->curbootfd, dstpath);
    fd = sopen(up->curbootfd, dstpath, O_WRONLY|O_CREAT, kCacheFileMode);
    if (fd == -1) {
        rval = errno; goto finish;
    }

    len = CFDataGetLength(bpdata);
    if (write(fd,CFDataGetBytePtr(bpdata),len) != len) {
        rval = errno; goto finish;
    }

    rval = 0;

finish:
    if (rval) {
        LOGERRxlate(up, dstpath, NULL, rval);
    }
    
    if (fd != -1)   close(fd);
    if (bpdata)     CFRelease(bpdata);

    return rval;
}

// correctly erase (hopefully old :) items in the Apple_Boot
static int
eraseRPS(struct updatingVol *up, char *toErase)
{
    int rval = ELAST+1;
    char path[PATH_MAX];
    struct stat sb;

    // if nothing to erase, return cleanly
    if (stat(toErase, &sb) == -1 && errno == ENOENT) {
        rval = 0;
        goto finish;
    }

    if (up->caches->erpropcache->rpath) {
        // pathc*() seed errno
        pathcpy(path, toErase);
        pathcat(path, up->caches->erpropcache->rpath);
        // szerofile() won't complain if it is missing
        if (szerofile(up->curbootfd, path))
            goto finish;
    }

    rval = sdeepunlink(up->curbootfd, toErase);

finish:
    if (rval) {
        OSKextLog(NULL, up->errLogSpec | kOSKextLogFileAccessFlag,
                  "%s - %s. errno %d %s", 
                  __FUNCTION__, toErase, errno, strerror(errno));
    }

    return rval;
}

static int
_writeFDEPropsToHelper(struct updatingVol *up, char *dstpath)
{
    int errnum, rval = ELAST + 1;   // everyone sets it?
    char *stage;
    CFDictionaryRef matching;       // IOServiceGetMatchingServices() releases
    io_service_t helper = IO_OBJECT_NULL;
    CFNumberRef unitNum = NULL;
    CFNumberRef partNum = NULL;
    int partnum;
    const void *keys[2], *vals[2];
    CFDictionaryRef props = NULL;
    io_service_t bearer = IO_OBJECT_NULL;
    CFStringRef partType = NULL;
    CFStringRef partBSD = NULL;
    char csbsd[DEVMAXPATHSIZE];

    stage = "check argument";
    if (up->onAPM) {
        rval = EINVAL; goto finish;
    }

    stage = "find current helper partition";
    if (!(matching = IOBSDNameMatching(kIOMasterPortDefault, 0, up->bsdname))){
        rval = ENOMEM; goto finish;
    }
    helper = IOServiceGetMatchingService(kIOMasterPortDefault, matching);
    matching = NULL;        // IOServiceGetMatchingService() released
    if (!helper) {
        rval = ENOENT; goto finish;
    }
    unitNum = (CFNumberRef)IORegistryEntryCreateCFProperty(helper,
                           CFSTR(kIOBSDUnitKey), nil, 0);
    if (!unitNum || CFGetTypeID(unitNum) != CFNumberGetTypeID()) {
        rval = ENODEV; goto finish;
    }
    partNum = (CFNumberRef)IORegistryEntryCreateCFProperty(helper,
                           CFSTR(kIOMediaPartitionIDKey), nil, 0);
    if (!partNum || CFGetTypeID(partNum) != CFNumberGetTypeID()) {
        rval = ENODEV; goto finish;
    }

    stage = "create description of corresponding data partition";
    CFNumberGetValue(partNum, kCFNumberIntType, &partnum);
    CFRelease(partNum);
    partNum = NULL;
    // in GPT, data the partition comes before the Apple_Boot
    if (--partnum <= 0) {
        rval = ENODEV; goto finish;
    }
    partNum = CFNumberCreate(nil, kCFNumberIntType, &partnum);
    if (!partNum) {
        rval = ENOMEM; goto finish;
    }
    // create property and matching dictionaries
    keys[0] = CFSTR(kIOMediaPartitionIDKey);
    vals[0] = partNum;
    keys[1] = CFSTR(kIOBSDUnitKey);
    vals[1] = unitNum;
    if (!(props = CFDictionaryCreate(nil, keys, vals, 2,
                                  &kCFTypeDictionaryKeyCallBacks,
                                  &kCFTypeDictionaryValueCallBacks))) {
        rval = ENOMEM; goto finish;
    }
    keys[0] = CFSTR(kIOProviderClassKey);
    vals[0] = CFSTR(kIOMediaClass);
    keys[1] = CFSTR(kIOPropertyMatchKey);
    vals[1] = props;
    if (!(matching = CFDictionaryCreate(nil, keys, vals, 2,
                                  &kCFTypeDictionaryKeyCallBacks,
                                  &kCFTypeDictionaryValueCallBacks))) {
        rval = ENOMEM; goto finish;
    }

    stage = "find & validate data partition";
    bearer = IOServiceGetMatchingService(kIOMasterPortDefault, matching);
    matching = NULL;        // IOServiceGetMatchingService() released
    if (!bearer) {
        rval = ENOENT; goto finish;
    }
    // extract BSD Name
    partBSD = (CFStringRef)IORegistryEntryCreateCFProperty(bearer,
                           CFSTR(kIOBSDNameKey), nil, 0);
    if (!partBSD || CFGetTypeID(partBSD) != CFStringGetTypeID()) {
        rval = ENODEV; goto finish;
    }
    if (!CFStringGetFileSystemRepresentation(partBSD, csbsd, sizeof(csbsd))){
        rval = EOVERFLOW; goto finish;
    }
    // the data partition's type must be Apple_CoreStorage
    partType = (CFStringRef)IORegistryEntryCreateCFProperty(bearer,
                            CFSTR(kIOMediaContentKey), nil, 0);
    if (!partType || CFGetTypeID(partType) != CFStringGetTypeID()) {
        rval = ENODEV; goto finish;
    }
    if (!CFEqual(partType, CFSTR(APPLE_CORESTORAGE_UUID))) {
        rval = ENODEV;
        LOGERRxlate(up, csbsd, "must be of type Apple_CoreStorage", rval);
        stage = NULL;   // logged our own error
        goto finish;
    }

    stage = NULL;       // writeCSFDEProps logs its own errors
    // writeCSFDEProps() uses csbsd's wipe key to encrypt the context data.
    if ((errnum=writeCSFDEProps(up->curbootfd,up->csfdeprops,csbsd,dstpath))){
        rval = errnum; goto finish;
    }

    // success!
    rval = 0;

finish:
    if (rval && stage) {
        OSKextLog(NULL, up->errLogSpec | kOSKextLogFileAccessFlag,
                  "%s() failed trying to %s", __func__, stage);
    }

    if (partBSD)                    CFRelease(partBSD);
    if (partType)                   CFRelease(partType);
    if (bearer != IO_OBJECT_NULL)   IOObjectRelease(bearer);
    if (props)                      CFRelease(props);
    if (partNum)                    CFRelease(partNum);
    if (unitNum)                    CFRelease(unitNum);
    if (helper != IO_OBJECT_NULL)   IOObjectRelease(helper);

    return rval;
}

static void
eraseRPSIfRecoveryBlessed(struct updatingVol *up, char *rpsDir)
{
    // if we can bless a Recovery OS, remove current files to free up space
    if (blessRecovery(up) == 0) {
        int bsderr;

        if ((bsderr = eraseRPS(up, rpsDir)) && errno != ENOENT) {
            LOGERRxlate(up, rpsDir, "couldn't free up space", bsderr);
        }
        // re-bless booters at the end
        // (This also copies them, but they're small compared to RPS.)
        up->doBooters = true;
    }
}

/* 
 * ucopyRPS - copy new RPS directory to "inactive" location
 * bails on any error because only a whole RPS dir makes sense
 */
static int
ucopyRPS(struct updatingVol *up)
{
    int bsderr, rval = ELAST + 1;   // generic safest
    char prevRPS[PATH_MAX], curRPS[PATH_MAX], discard[PATH_MAX];
    char *erdir;
    unsigned i;
    char srcpath[PATH_MAX], dstpath[PATH_MAX];
#if DEV_KERNEL_SUPPORT
    CFStringRef my_kcsuffix     = NULL;     // must release
    Boolean copiedPrefKernel    = false;
#endif
    COMPILE_TIME_ASSERT(sizeof(BOOTPLIST_NAME)==sizeof(BOOTPLIST_APM_NAME));
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Copying files used by the booter.");

    if ((bsderr = FindRPSDir(up, prevRPS, curRPS, discard))) {
        rval = bsderr; goto finish;     // error logged by function
    }

    if (up->flatTarget[0] || up->useOnceDir) {
        // copy desired target into dstdir
        pathcpy(up->dstdir, up->curMount);
        if (up->useOnceDir) {
            pathcat(up->dstdir, kBRBootOnceDir);
        }
        pathcat(up->dstdir, up->flatTarget);
        erdir = curRPS;
        if ((up->blessSpec & kBRBlessOnce) == 0 && (up->blessSpec & kBRBlessRecovery) != 0) {
            erdir = prevRPS;
            eraseRPSIfRecoveryBlessed(up, curRPS);
        }
    } else {
        // we're going to copy into the currently-inactive directory
        pathcpy(up->dstdir, prevRPS);
        erdir = prevRPS;
        eraseRPSIfRecoveryBlessed(up, curRPS);
    }

    // remove any stray target directory
    if ((bsderr = eraseRPS(up, up->dstdir))) {
        rval = bsderr; goto finish;     // error logged by function
    }

    // create the directory (RPS should not exist?)
    if ((bsderr = sdeepmkdir(up->curbootfd, up->dstdir, kCacheDirMode))) {
        rval = bsderr; LOGERRxlate(up, up->dstdir, NULL, rval); goto finish;
    }

#if DEV_KERNEL_SUPPORT
    // NOTE - copy_kcsuffix will return ".release" suffix when kcsuffix is
    // "kcsuffix=" or "kcsuffix=release".  Since the "release" kernel and
    // prelinkedkernel file names do NOT have a suffix the for loop for
    // extraKernelCachePaths will not match via the CFStringHasSuffix() call and
    // we will drop out of the for loop with copiedPrefKernel == false. This is
    // by design.  The copy of the release prelinkedkernel will happen lower down.
    my_kcsuffix = copy_kcsuffix();
    if (up->caches->extraKernelCachePaths && my_kcsuffix) {
        int     i;
        for (i = 0; i < up->caches->nekcp; i++) {
            cachedPath *curItem = &up->caches->extraKernelCachePaths[i];
            
            // until 16140679 gets fixed we can only copy 1 prelinkedkernel to
            // Apple_Boot partitions.  We use boot-arg kcsuffix to give us a
            // hint about which prelinkedkernel to copy - 16929470
            CFStringRef tempString;
            Boolean     hasSuffix;
            tempString = CFStringCreateWithCString(NULL,
                                                   curItem->rpath,
                                                   kCFStringEncodingUTF8);
            if (tempString == NULL) {
                continue;
            }
            hasSuffix = CFStringHasSuffix(tempString, my_kcsuffix);
            SAFE_RELEASE_NULL(tempString);
            if (hasSuffix == false) {
                continue;
            }
            pathcpy(srcpath, up->caches->root);
            pathcat(srcpath, curItem->rpath);
            pathcpy(dstpath, up->dstdir);
            pathcat(dstpath, curItem->rpath);
            OSKextLog(NULL, kOSKextLogGeneralFlag|kOSKextLogDetailLevel,
                      "copying %s to %s", srcpath, up->dstdir);
            bsderr = scopyitem(up->caches->cachefd,
                               srcpath,
                               up->curbootfd,
                               dstpath);
            if (bsderr) {
                rval = bsderr == -1 ? errno : bsderr;
                OSKextLog(NULL,up->errLogSpec,"Error %d copying %s to %s: %s",
                          rval, srcpath, dstpath, strerror(rval));
                goto finish;
            }
            copiedPrefKernel = true;
        } // for loop...
    }
#endif

    // and loop
    for (i = 0; i < up->caches->nrps; i++) {
        cachedPath *curItem = &up->caches->rpspaths[i];

        // 15860955: skip release kernel if preferred has already been copied
        if (copiedPrefKernel && curItem == up->caches->kext_boot_cache_file) {
           continue;
        }

        pathcpy(srcpath, up->caches->root);
        pathcat(srcpath, curItem->rpath);
        pathcpy(dstpath, up->dstdir);
        // EfiLoginUI.a still digs down to its cache dirs
        if ((up->flatTarget[0] || up->useOnceDir)
                && curItem != up->caches->efidefrsrcs
                && curItem != up->caches->efiloccache) {
            /* XX 10561671: basename unsafe */
            pathcat(dstpath, "/");
            pathcat(dstpath, basename(curItem->rpath));
        } else {
            pathcat(dstpath, curItem->rpath);
        }

        // check for special files; first Boot.plist
        if (curItem == up->caches->bootconfig) {
            // PR-5115900 - call it com.apple.boot.plist on APM since Tiger
            // (since Tiger bless scribbles on com.apple.Boot.plist)
            if (up->onAPM) {
                char * plistNamePtr;
                // see assert above
                plistNamePtr = strstr(dstpath, BOOTPLIST_NAME);
                if (plistNamePtr) {
                    strncpy(plistNamePtr, BOOTPLIST_APM_NAME, strlen(BOOTPLIST_NAME));
                }
            }
            // write customized com.apple.Boot.plist data
            if ((bsderr = writeBootPrefs(up, dstpath))) {
                rval = bsderr; goto finish;     // error logged by function
            }
        } else if (curItem == up->caches->erpropcache && up->csfdeprops && up->onAPM == false) {

            // use csfdeprops
            if ((bsderr = _writeFDEPropsToHelper(up, dstpath))) {                      
                rval = bsderr; goto finish;     // error logged by function
            }

        } else {
            // could deny zero-size cookies, busted Mach-O, etc here
            // scopyitem creates any intermediate directories
            OSKextLog(NULL, kOSKextLogGeneralFlag|kOSKextLogDetailLevel,
                      "copying %s to %s", srcpath, up->dstdir);
            bsderr=scopyitem(up->caches->cachefd,srcpath,up->curbootfd,dstpath);
            if (bsderr) {
                rval = bsderr == -1 ? errno : bsderr;
                // erpropcache, efiloccache are optional
                if (((curItem == up->caches->erpropcache) || (curItem == up->caches->efiloccache)) && (rval == ENOENT)) {
                    // ENOENT for these items is fine
                    continue;
                } else {
                    OSKextLog(0,up->errLogSpec,"Error %d copying %s to %s: %s",
                              rval, srcpath, dstpath, strerror(rval));
                    goto finish;
                }
            }
        }
    }

    // XX EFI is happier if there is a SystemVersion.plist it can find

    // 10561691 wasn't fixed until 10.8 so we implement "mostly flat"
    // for 10.7-era systems when flatTarget is set.
    // re-write correctly-encrypted context to secondary location
    if ((up->flatTarget[0] || up->useOnceDir)
            && up->caches->erpropTSOnly == false && up->onAPM == false
            && up->caches->erpropcache && up->csfdeprops) {
        pathcpy(dstpath, erdir);
        pathcat(dstpath, up->caches->erpropcache->rpath);
        if ((bsderr = _writeFDEPropsToHelper(up, dstpath))) {
            rval = bsderr; goto finish;     // error logged by function
        }

        if (up->caches->efidefrsrcs) {
            pathcpy(srcpath, up->caches->root);
            pathcat(srcpath, up->caches->efidefrsrcs->rpath);
            pathcpy(dstpath, erdir);
            pathcat(dstpath, up->caches->efidefrsrcs->rpath);
            bsderr=scopyitem(up->caches->cachefd,srcpath,up->curbootfd,dstpath);
            if (bsderr) {
                rval = bsderr == -1 ? errno : bsderr;
                OSKextLog(NULL,up->errLogSpec,"Error %d copying %s to %s: %s",
                          rval, srcpath, dstpath, strerror(rval));
                goto finish;
            }
        }
    }

    // success
    rval = 0;

finish:
#if DEV_KERNEL_SUPPORT
    SAFE_RELEASE(my_kcsuffix);
#endif
    return rval;
}

/******************************************************************************
* ucopyMisc writes misc files to .new (inactive) name
******************************************************************************/
static int
ucopyMisc(struct updatingVol *up)
{
    int bsderr, rval = -1;
    unsigned i, nprocessed = 0;
    char srcpath[PATH_MAX], dstpath[PATH_MAX];
    struct stat sb;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Copying files read before the booter runs.");
   
    for (i = 0; i < up->caches->nmisc; i++) {
        pathcpy(srcpath, up->caches->root);
        pathcat(srcpath, up->caches->miscpaths[i].rpath);
        makebootpath(dstpath, up->caches->miscpaths[i].rpath);
        pathcat(dstpath, ".new");

        if (stat(srcpath, &sb) == 0) { 
            // file exists and is accessible
            if ((bsderr = scopyitem(up->caches->cachefd, srcpath,
                                    up->curbootfd, dstpath))) {
                if (bsderr == -1)  bsderr = errno;
                OSKextLog(NULL, up->errLogSpec, "Error %d copying %s to %s: %s",
                          bsderr, srcpath, dstpath, strerror(bsderr));
                continue;
            }
        } else if (errno != ENOENT) {
            continue;
        }

        nprocessed++;
    }

    if (nprocessed == i) {
        rval = 0;
    } else {
        rval = errno;
    }

finish:
    if (rval) {
        LOGERRxlate(up, __func__, "failure copying pre-booter files", rval);
    }

    return rval;
}

/******************************************************************************
* moveLabels() deactivates the but preserves it for later
* activateMisc() will move these back if needed
* no label -> hint of indeterminate state (label key in plist/other file??)
* XX put/switch in some sort of "(updating!)" label (see BL[ess] routines)
******************************************************************************/
static int
moveLabels(struct updatingVol *up)
{
    int rval = -1;
    char path[PATH_MAX];
    struct stat sb;
    int fd = -1;
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Moving aside old label.");

    // pathc*() seed errno
    makebootpath(path, up->caches->label->rpath);
    if (0 == (stat(path, &sb))) {
        char newpath[PATH_MAX];
        unsigned char nulltype[32] = {'\0', };

        // rename
        pathcpy(newpath, path);
        pathcat(newpath, NEWEXT);
        rval = srename(up->curbootfd, path, newpath);
        if (rval)       goto finish;

        // remove magic type/creator
        if (-1 == (fd=sopen(up->curbootfd, newpath, O_RDWR, 0)))  goto finish;
        if(fsetxattr(fd,XATTR_FINDERINFO_NAME,&nulltype,sizeof(nulltype),0,0)) {
            goto finish;
        }
    } 

    up->changestate = noLabel;
    rval = 0;

finish:
    if (fd != -1)   close(fd);

    if (rval) {
        OSKextLog(NULL, up->errLogSpec,
                  "%s - Error moving aside old label. errno %d %s.", 
                  __FUNCTION__, errno, strerror(errno));
   }

    return rval;
}

/******************************************************************************
* nukeBRLabels gets rid of the label and .contentDetails files
* no label -> hint of indeterminate state (label key in plist/other file?)
* someday: some sort of "(updating!)" label?
******************************************************************************/
static int
nukeBRLabels(struct updatingVol *up)
{
    int rval = EOVERFLOW;       // path*()
    int opres, firstErrno, firstErr = 0;
    char labelp[PATH_MAX], dstparent[PATH_MAX];
    struct stat sb;
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Removing current disk label.");

    // .disk_label
    makebootpath(labelp, up->caches->label->rpath);
    if (0 == (stat(labelp, &sb))) {
        opres = sunlink(up->curbootfd, labelp);
        RECERR(up, opres, "error removing label" /*NULL w/9217695*/);
    } else {
        errno = 0;
    }

    // .disk_label_2x
    pathcpy(labelp, up->curMount);
    if (up->useOnceDir) {
        pathcat(labelp, kBRBootOnceDir);
    }
    pathcat(labelp, up->caches->label->rpath);
    pathcat(labelp, SCALE_2xEXT);       // append extension
    if (0 == (stat(labelp, &sb))) {
        opres = sunlink(up->curbootfd, labelp);
        RECERR(up, opres, "error removing .contentDetails" /*NULL w/9217695*/);
    } else {
        errno = 0;
    }

    // .disk_label.contentsDetail
    pathcpy(labelp, up->curMount);
    if (up->useOnceDir) {
        pathcat(labelp, kBRBootOnceDir);
    }
    pathcat(labelp, up->caches->label->rpath);
    pathcat(labelp, CONTENTEXT);        // append extension
    if (0 == (stat(labelp, &sb))) {
        opres = sunlink(up->curbootfd, labelp);
        RECERR(up, opres, "error removing " CONTENTEXT /*NULL w/9217695*/);
    } else {
        errno = 0;
    }

    // and possible .root_uuid
    makebootpath(labelp, up->caches->label->rpath);
    pathcpy(dstparent, dirname(labelp));
    pathcpy(labelp, dstparent);
    pathcat(labelp, "/" kBRRootUUIDFile);
    if (0 == (stat(labelp, &sb))) {
        opres = sunlink(up->curbootfd, labelp);
        RECERR(up, opres, "error removing " kBRRootUUIDFile /*NULL w/9217695*/);
    } else {
        errno = 0;
    }

    up->changestate = noLabel;

    if (firstErr == -1)     errno = firstErrno;
    rval = firstErr;

finish:
    if (rval)
        OSKextLog(NULL, kOSKextLogErrorLevel, "Error removing disk label.");

    return rval;
}

/******************************************************************************
* ucopyBooters unlink/copies down booters but doesn't bless them
******************************************************************************/
static int
ucopyBooters(struct updatingVol *up)
{
    int rval = ELAST + 1;
    int bsderr;
    char srcpath[PATH_MAX], oldpath[PATH_MAX];
    int nbooters = 0;

    if (up->caches->ofbooter.rpath[0])      nbooters++;
    if (up->caches->efibooter.rpath[0])     nbooters++;
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Copying new booter%s.", nbooters == 1 ? "" : "s");
    
    // copy BootX, boot.efi
    up->changestate = copyingOFBooter;
    if (up->caches->ofbooter.rpath[0]) {
        // pathc*() seed errno
        pathcpy(srcpath, up->caches->root);
        pathcat(srcpath, up->caches->ofbooter.rpath);   // <root>/S/L/CS/BootX
        makebootpath(up->ofdst, up->caches->ofbooter.rpath); // <boot>/../BootX
        pathcpy(oldpath, up->ofdst);
        pathcat(oldpath, OLDEXT);                  // <boot>/S/L/CS/BootX.old

        (void)sunlink(up->curbootfd, oldpath);
        bsderr = srename(up->curbootfd, up->ofdst, oldpath);
        if (bsderr && errno !=ENOENT) {
            OSKextLog(NULL, up->errLogSpec, 
                      "%s - Error rename old %s new %s",
                      __FUNCTION__, up->ofdst, oldpath);
            goto finish;
        }
        if ((bsderr = scopyitem(up->caches->cachefd, srcpath,
                                up->curbootfd, up->ofdst))) {
            rval = bsderr == -1 ? errno : bsderr;
            if (!(up->opts & kBRUHelpersOptional)) {
                OSKextLog(NULL,up->errLogSpec,"Error %d copying %s to %s: %s",
                          rval, srcpath, up->ofdst, strerror(rval));
            }
            goto finish;
        }
    }

    up->changestate = copyingEFIBooter;
    if (up->caches->efibooter.rpath[0]) {
        // pathc*() seed errno
        pathcpy(srcpath, up->caches->root);
        pathcat(srcpath, up->caches->efibooter.rpath);   // ... boot.efi
        makebootpath(up->efidst, up->caches->efibooter.rpath);
        pathcpy(oldpath, up->efidst);
        pathcat(oldpath, OLDEXT);

        (void)sunlink(up->curbootfd, oldpath);
        bsderr = srename(up->curbootfd, up->efidst, oldpath);
        if (bsderr && errno != ENOENT) {
            OSKextLog(NULL, up->errLogSpec, 
                      "%s - Error rename old %s new %s",
                      __FUNCTION__, up->efidst, oldpath);
            goto finish;
        }
        if ((bsderr = scopyitem(up->caches->cachefd, srcpath,
                                up->curbootfd, up->efidst))) {
            if (!(up->opts & kBRUHelpersOptional)) {
                rval = bsderr == -1 ? errno : bsderr;
                OSKextLog(NULL,up->errLogSpec,"Error %d copying %s to %s: %s",
                          rval, srcpath, up->efidst, strerror(rval));
            }
            goto finish;
        }
    }

    up->changestate = copiedBooters;
    rval = 0;

finish:
    // all goto paths log

    return rval;
}


// booters have worst critical:fragile ratio (basically point of no return)
/******************************************************************************
* bless recently-copied booters
* operatens entirely on up->??dst which allows revertState to use it ..?
******************************************************************************/
#define CLOSE(fd) do { (void)close(fd); fd = -1; } while(0)
static int
activateBooters(struct updatingVol *up)
{
    int errnum, rval = ELAST + 1;
    int fd = -1;
    uint64_t vinfo[8] = { 0, };
    struct stat sb;
    char parent[PATH_MAX];
    int nbooters = 0;
    BLContext blctx = { 0, BRBLLogFunc, NULL };

    if (up->caches->ofbooter.rpath[0])      nbooters++;   
    if (up->caches->efibooter.rpath[0])     nbooters++;    

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Activating new booter%s.", nbooters == 1 ? "" : "s");

    // flush everything in this helper partition to disk
    if ((errnum = fcntl(up->curbootfd, F_FULLFSYNC))) {
        rval = errnum; goto finish;
    }
    
    // activate BootX, boot.efi
    up->changestate = activatingOFBooter;
    if (up->caches->ofbooter.rpath[0]) {
        unsigned char tbxichrp[32] = {'t','b','x','i','c','h','r','p','\0',};

        // apply type/creator (assuming same folder as previous, now active)
        if (-1==(fd=sopen(up->curbootfd, up->ofdst, O_RDONLY, 0))) {
            rval = errno; goto finish;
        }
        if(fsetxattr(fd,XATTR_FINDERINFO_NAME,&tbxichrp,sizeof(tbxichrp),0,0)){
            rval = errno; goto finish;
        }
        CLOSE(fd);

        // get fileID of booter's enclosing folder 
        pathcpy(parent, dirname(up->ofdst));
        if (-1 == (fd=sopen(up->curbootfd, parent, O_RDONLY, 0))
                    || fstat(fd, &sb)) {
            rval = errno; goto finish;
        }
        CLOSE(fd);
        vinfo[kSystemFolderIdx] = sb.st_ino;
    }

    up->changestate = activatingEFIBooter;
    if (up->caches->efibooter.rpath[0]) {
        // get file ID
        if (-1==(fd=sopen(up->curbootfd, up->efidst, O_RDONLY, 0))
                    || fstat(fd, &sb)) {
            rval = errno; goto finish;
        }
        CLOSE(fd);
        vinfo[kEFIBooterIdx] = sb.st_ino;

        // get folder ID of enclosing folder if not provided by ofbooter
        if (!vinfo[0]) {
            pathcpy(parent, dirname(up->efidst));
            if (-1 == (fd=sopen(up->curbootfd, parent, O_RDONLY, 0)) 
                    || fstat(fd, &sb)) {
                rval = errno; goto finish;
            }
            CLOSE(fd);
            vinfo[kSystemFolderIdx] = sb.st_ino;
        }
    }

    // configure blessing as requested
    // FSDefault is a single unique bit.
    if (up->blessSpec & kBRBlessFSDefault) {
        if ((errnum = sBLSetBootInfo(up, vinfo))) {
            rval = errnum; goto finish;    
        }
    }
    // BlessFull = (FSDefault | setNVRAM)
    if (up->blessSpec == kBRBlessFull) {
        if (BLSetEFIBootDevice(&blctx, up->bsdname)) {
            rval = ENODEV; goto finish;
        }
    }
    // BlessOnce is a unique bit. Use BLSetEFIBootDeviceOnce() if we
    // just made the target the default for the filesystem.
    if (up->blessSpec & kBRBlessOnce) {
        if (up->blessSpec & kBRBlessFSDefault) {
            if (BLSetEFIBootDeviceOnce(&blctx, up->bsdname)) {
                rval = ENODEV; goto finish;
            }
        } else {
            if (BLSetEFIBootFileOnce(&blctx, up->efidst)) {
                rval = ENODEV; goto finish;
            }
        }
    }
    
    up->changestate = activatedBooters;

    // success
    rval = 0;

finish:
    if (fd != -1)   close(fd);

    if (rval)
        OSKextLog(NULL, kOSKextLogErrorLevel, "Error activating booter.");

    return rval;
}

/******************************************************************************
* leap-frog w/rename()
******************************************************************************/
static int
activateRPS(struct updatingVol *up)
{
    int rval = ELAST + 1;
    char prevRPS[PATH_MAX], curRPS[PATH_MAX], nextRPS[PATH_MAX];
    
    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Activating files used by the booter.");

    // if using default RPS dirs, make fresh one current
    if (up->flatTarget[0] == '\0' && up->useOnceDir == false) {
        if (FindRPSDir(up, prevRPS, curRPS, nextRPS))   goto finish;

        // if current != the one we just populated
        if (strncmp(curRPS, up->dstdir, PATH_MAX) != 0) {
            // rename prev -> next ... done!?
            if (srename(up->curbootfd, prevRPS, nextRPS))   goto finish;
        }
    }

    // thwunk everything to disk (now that essential boot files are in place)
    if (fcntl(up->curbootfd, F_FULLFSYNC))              goto finish;

    rval = 0;

finish:
    if (rval) {
        OSKextLog(NULL, kOSKextLogErrorLevel,
              "Error activating files used by the booter.");
    }

    return rval;
}


/******************************************************************************
* activateMisc renames .new files to final names and relabels the volumes
* active label indicates an updated helper partition
* - construct new label with a trailing number as appropriate
* - use BLGenerateLabelData() and overwrite any copied-down label
* X need to be consistent throughout regarding missing misc files (esp. label?)
******************************************************************************/
/*
 * writeLabels() writes correctly-formatted label and related files.
 * These files should be removed first via nukeLabels().
 *
 * Since com.apple.recovery.boot is generally only present in CoreStorage
 * helpers, the net effect of writeLabel()'s policy of
 *     if (up->bootIdx == 0 || up->detectedRecovery) {
 * is that CoreStorage will get .root_uuid files (and matching label data)
 * in all Apple_Boot helpers while non-CS (AppleRAID, third party) will get
 * 'Mac HD', 'Mac HD 2', ... 'Mac HD <n>' in their helpers.  The absence of
 * .root_uuid in subsequent helpers should prevent EFI from merging any of
 * these non-CS helpers.  See 11129639 and related for more details.
 */

// see makebootpath() at top of file
#define MAKEBOOTPATHcont(path, rpath) do { \
                                    PATHCPYcont(path, up->curMount); \
                                    if (up->useOnceDir) { \
                                        PATHCATcont(path, kBRBootOnceDir); \
                                    } \
                                    if (up->flatTarget[0] || up->useOnceDir) { \
                                        PATHCATcont(path, up->flatTarget); \
                                        /* XXX 10561671: basename unsafe */ \
                                        PATHCATcont(path, "/"); \
                                        PATHCATcont(path, basename(rpath)); \
                                    } else { \
                                        PATHCATcont(path, rpath); \
                                    } \
                                } while(0)
static int
activateMisc(struct updatingVol *up)     // rename the .new
{
    int rval = ELAST + 1;
    char path[PATH_MAX], opath[PATH_MAX];
    unsigned i = 0, nprocessed = 0;
    int fd = -1;
    struct stat sb;
    unsigned char tbxjchrp[32] = { 't','b','x','j','c','h','r','p','\0', };
   
    if (up->doMisc) {
        OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
                  "Activating files used before the booter runs.");
        
        // do them all
        for (i = 0; i < up->caches->nmisc; i++) {
            MAKEBOOTPATHcont(path, up->caches->miscpaths[i].rpath);
            if (strlcpy(opath, path, PATH_MAX) >= PATH_MAX)     continue;
            if (strlcat(opath, NEWEXT, PATH_MAX) >= PATH_MAX)   continue;

            if (stat(opath, &sb) == 0) {
                if (srename(up->curbootfd, opath, path))        continue;
            }

            nprocessed++;
        }
    }

    makebootpath(path, up->caches->label->rpath);
        // move label back
        char newpath[PATH_MAX];

        pathcpy(newpath, path);     // just rename
        pathcat(newpath, NEWEXT);
        (void)srename(up->curbootfd, newpath, path);

    // assign type/creator to the label
    if (0 == (stat(path, &sb))) {
        if (-1 == (fd = sopen(up->curbootfd, path, O_RDWR, 0)))   goto finish;

        if (fsetxattr(fd,XATTR_FINDERINFO_NAME,&tbxjchrp,sizeof(tbxjchrp),0,0))
            goto finish;
        close(fd); fd = -1;
    }

    rval = (i != nprocessed);

finish:
    if (fd != -1)   close(fd);

    if (rval) {
        OSKextLog(NULL, kOSKextLogErrorLevel,
                  "Error activating files used before the booter runs.");
    }

    return rval;
}

/******************************************************************************
* get rid of everything "extra"
******************************************************************************/
static int
nukeFallbacks(struct updatingVol *up)
{
    int rval = 0;               // OR-ative return value
    int bsderr;
    char delpath[PATH_MAX];
    struct bootCaches *caches = up->caches;

    OSKextLog(NULL, kOSKextLogDetailLevel | kOSKextLogGeneralFlag,
              "Cleaning up fallbacks.");

    // using pathcpy b/c if that's failing, it's worth bailing
    // XX should probably only try to unlink if present

    // maybe mount failed (in which case there aren't any fallbacks)
    if (up->curMount[0] == '\0')    goto finish;

    // if needed, unlink .old booters
    if (up->doBooters) {
        if (caches->ofbooter.rpath[0]) {
            makebootpath(delpath, caches->ofbooter.rpath);
            pathcat(delpath, OLDEXT);
            if ((bsderr = sunlink(up->curbootfd, delpath)) && errno != ENOENT) {
                rval |= bsderr;
            }
        }
        if (caches->efibooter.rpath[0]) {
            makebootpath(delpath, caches->efibooter.rpath);
            pathcat(delpath, OLDEXT);
            if ((bsderr = sunlink(up->curbootfd, delpath)) && errno != ENOENT) {
                rval |= bsderr;
            }
        }
    }

    // if needed, erase prevRPS
    // which, conveniently, will be right regardless of whether we succeeded
    if (up->doRPS) {
        char ignore[PATH_MAX];

        if (0 == FindRPSDir(up, delpath, ignore, ignore)) {
            // eraseRPS ignores if missing (and logs other errors)
            rval |= eraseRPS(up, delpath);
        }
    }

finish:
    if (rval)
        OSKextLog(NULL, kOSKextLogErrorLevel, "Error cleaning up fallbacks.");

    return rval;
}

#if 0
/*********************************************************************
// XXX not yet used / tested
*********************************************************************/
static int
kill_kextd(void)
{
    int           result         = -1;
    kern_return_t kern_result    = kOSReturnError;
    mach_port_t   bootstrap_port = MACH_PORT_NULL;
    mach_port_t   kextd_port     = MACH_PORT_NULL;
    int           kextd_pid      = -1;

    kern_result = task_get_bootstrap_port(mach_task_self(), &bootstrap_port);
    if (kern_result != kOSReturnSuccess) {
        goto finish;
    }

    kern_result = bootstrap_look_up(bootstrap_port,
        (char *)KEXTD_SERVER_NAME, &kextd_port);
    if (kern_result != kOSReturnSuccess) {
        goto finish;
    }

    kern_result = pid_for_task(kextd_port, &kextd_pid);
    if (kern_result != kOSReturnSuccess) {
        goto finish;
    }

    result = kill(kextd_pid, SIGKILL);
    if (-1 == result) {
        OSKextLog(/* kext */ NULL,
            kOSKextLogErrorLevel | kOSKextLogFileAccessFlag,
             "kill kextd failed - %s.", strerror(errno));
    }

finish:
    if (kern_result != kOSReturnSuccess) {
        OSKextLog(/* kext */ NULL,
            kOSKextLogErrorLevel | kOSKextLogFileAccessFlag,
             "kill kextd failed - %s.", safe_mach_error_string(kern_result));
    }
    return result;
}

/******************************************************************************
// XXX not yet used / tested  
******************************************************************************/
int
renameBootcachesPlist(
    char * hostVolume,
    char * oldPlistPath,
    char * newPlistPath)
{
    int    result            = -1;
    int    bootcachesPlistFd = -1;
    char * errorMessage      = NULL;
    char * errorPath         = NULL;
    char   oldname[PATH_MAX];
    char   newname[PATH_MAX];
    char * kextcacheArgs[] = {
        "/usr/sbin/kextcache",
        "-f",
        "-u",
        NULL, // replace with hostVolume
        NULL };

    errorMessage = "path concatenation error";
    errorPath = hostVolume;

    if (strlcpy(oldname, hostVolume, PATH_MAX) >= PATH_MAX) {
        goto finish;
    }
    if (strlcpy(newname, hostVolume, PATH_MAX) >= PATH_MAX) {
        goto finish;
    }

    errorPath = oldPlistPath;
    if (strlcpy(oldname, oldPlistPath, PATH_MAX) >= PATH_MAX) {
        goto finish;
    }

    errorPath = newPlistPath;
    if (strlcpy(newname, newPlistPath, PATH_MAX) >= PATH_MAX) {
        goto finish;
    }

    errorPath = oldname;
    bootcachesPlistFd = open(oldname, O_RDONLY);
    if (-1 == bootcachesPlistFd) {
        errorMessage = strerror(errno);
        goto finish;
    }
    
    if (-1 == srename(bootcachesPlistFd, oldname, newname)) {
        errorMessage = "rename failed.";
        goto finish;
    }
    
    errorMessage = "couldn't kill kextd";
    if (-1 == kill_kextd()) {
        goto finish;
    }

   /* Do we want to check fork_program's return value?
    */
    kextcacheArgs[3] = hostVolume;
    result = fork_program(kextcacheArgs[0], kextcacheArgs, true /* wait */);

finish:
    if (errorMessage) {
        OSKextLog(/* kext */ NULL,
            kOSKextLogErrorLevel | kOSKextLogFileAccessFlag,
             "%s - %s.", errorPath, errorMessage);
    }
    if (bootcachesPlistFd >= 0) {
        close(bootcachesPlistFd);
    }
    return result;
}
#endif      // UNUSED

/******************************************************************************
* takeVolumeForPath turns the path into a volume UUID and locks with kextd
******************************************************************************/
// upstat() stat()s "up" the path if a file doesn't exist
static int
upstat(const char *path, struct stat *sb, struct statfs *sfs)
{
    int rval = ELAST+1;
    char buf[PATH_MAX], *tpath = buf;
    struct stat defaultsb;

    if (strlcpy(buf, path, PATH_MAX) > PATH_MAX)        goto finish;

    if (!sb)    sb = &defaultsb;
    while ((rval = stat(tpath, sb)) == -1 && errno == ENOENT) {
        // "." and "/" should always exist, but you never know
        if (tpath[0] == '.' && tpath[1] == '\0')  goto finish;
        if (tpath[0] == '/' && tpath[1] == '\0')  goto finish;
        tpath = dirname(tpath);     // Tiger's dirname() took const char*
    }

    // call statfs if the caller needed it
    if (sfs)
        rval = statfs(tpath, sfs);

finish:
    if (rval) {
        OSKextLog(/* kext */ NULL,
            kOSKextLogWarningLevel | kOSKextLogFileAccessFlag,
                "Couldn't find volume for %s.", path);
    }

    return rval;
}


/******************************************************************************
* theoretically, takeVolumeForPaths() ensured all paths are on the given
* volume, then locked
******************************************************************************/
// int takeVolumeForPaths(char *volPath)

/******************************************************************************
* takeVolumeForPath() is all we ended up needing ...
* can return success if a lock isn't needed
* can return failure if sBRUptLock is already in use
******************************************************************************/
#define WAITFORLOCK 1
int
takeVolumeForPath(const char *path)
{
    int           rval     = ELAST + 1;
    int           lckres   = 0;
    kern_return_t macherr  = KERN_SUCCESS;
    const char    *volPath = "<unknown>";  // llvm can't track lckres/macherr
    mach_port_t   taskport = MACH_PORT_NULL;
    struct statfs sfs;

    if (getenv("_com_apple_kextd_skiplocks")) {
        /* Skip locking if we've already taken it */
        rval = 0;
        goto finish;
    }

    if (geteuid() != 0) {
        // kextd shouldn't be watching anything you can touch
        // and ignores locking requests from non-root anyway
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogGeneralFlag,
                 "Warning: non-root can't lock the volume for %s", path);
        rval = 0;
        goto finish;
    }

    // look up kextd port if not cached
    // XX if there's a way to know kextd isn't already running, we could skip
    // unnecessarily bringing it up in the boot-time case (see 5108882).
    if (!sKextdPort) {
        macherr=bootstrap_look_up(bootstrap_port,KEXTD_SERVER_NAME,&sKextdPort);
        if (macherr)  goto finish;
    }

    // get the volume's UUID
    if ((rval = upstat(path, NULL, &sfs)))      goto finish;
    volPath = sfs.f_mntonname;
    if ((rval = copyVolumeInfo(volPath,&s_vol_uuid,NULL,NULL,NULL))) {
        goto finish;
    }

    // allocate a port to pass (in case we die -- kernel cleans up on exit())
    taskport = mach_task_self();
    if (taskport == MACH_PORT_NULL)  goto finish;
    macherr = mach_port_allocate(taskport,MACH_PORT_RIGHT_RECEIVE,&sBRUptLock);
    if (macherr)  goto finish;

    // try to take the lock; warn if it's busy and then wait for it
    macherr = kextmanager_lock_volume(sKextdPort, sBRUptLock, s_vol_uuid,
                                      !WAITFORLOCK, &lckres);
    if (macherr)        goto finish;

    // 5519500: sleep until kextd is up and running (w/diskarb, etc)
    while (lckres == EAGAIN) {
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "kextd wasn't ready; waiting 10 seconds and trying again.");
        sleep(10);
        macherr = kextmanager_lock_volume(sKextdPort, sBRUptLock, s_vol_uuid,
                                          !WAITFORLOCK, &lckres);
        if (macherr)    goto finish;
    }

    // With kextd set up, we sleep until the volume is free.
    // WAITFORLOCK should cause the function not to return w/o the lock
    // but 8679674 suggested something was going awry so we'll retry.
    while (lckres == EBUSY) {
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "%s locked; waiting for lock.", volPath);
        macherr = kextmanager_lock_volume(sKextdPort, sBRUptLock, s_vol_uuid,
                                          WAITFORLOCK, &lckres);
        if (macherr)    goto finish;
        if (lckres == 0) {
            OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
                "Lock acquired; proceeding.");
        }
    }


    // kextd might not be watching this volume (isn't currently competing)
    // so we set our success to the existance of the volume's root
    if (lckres == ENOENT) {
        struct stat sb;
        rval = stat(volPath, &sb);
        if (rval == 0) {
            OSKextLog(NULL, kOSKextLogProgressLevel | kOSKextLogIPCFlag,
                "Note: kextd not watching %s; proceeding w/o lock", volPath);
        }
    } else {
        rval = lckres;
    }

finish:
    if (sBRUptLock != MACH_PORT_NULL && (lckres != 0 || macherr)) {
        mach_port_mod_refs(taskport, sBRUptLock, MACH_PORT_RIGHT_RECEIVE, -1);
        sBRUptLock = MACH_PORT_NULL;
    }

    /* XX needs unraveling XX */
    // if kextd isn't competing with us, then we didn't need the lock
    if (macherr == BOOTSTRAP_UNKNOWN_SERVICE ||
            macherr == MACH_SEND_INVALID_DEST) {
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "Warning: kextd unavailable; proceeding w/o lock for %s", volPath);
        rval = 0;
    } else if (macherr) {
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "Couldn't lock %s: %s (%x).", path,
            safe_mach_error_string(macherr), macherr);
        rval = macherr;
    } else if (rval) {
        // dump rval
        if (rval == -1)     rval = errno;
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "Couldn't lock %s: %s", path, strerror(rval));
    } else {
        /* Counter tells putVolumeForPath() when it's okay to drop the lock. */
        sBRUptLockCtr++;

        /*
         * If this call created the lock, make sure future calls to
         * takeVolumeForPath, in children or otherwise, don't attempt to retake it
         */
        if (sBRUptLock && sBRUptLockCtr == 1) {
            setenv("_com_apple_kextd_skiplocks", "1", 1);
        }
    }

    return rval;
}

/******************************************************************************
* putVolumeForPath will unlock the relevant volume, passing 'status' to
* inform kextd whether we succeded, failed, or just need more time
******************************************************************************/
int
putVolumeForPath(const char *path, int status)
{
    int  rval      = KERN_SUCCESS;
    bool wasLocked = false;

    // if not locked, don't sweat it
    if (sBRUptLock == MACH_PORT_NULL) {
        goto finish;
    }
    wasLocked = true;

    /* Don't unlock until calls to takeVolumeForPath and putVolumeForPath are balanced */
    if (sBRUptLockCtr > 1) {
        goto finish;
    }

    rval = kextmanager_unlock_volume(sKextdPort,sBRUptLock,s_vol_uuid,status);

    // tidy up; the server will clean up its stuff if we die prematurely
    mach_port_mod_refs(mach_task_self(),sBRUptLock,MACH_PORT_RIGHT_RECEIVE,-1);
    sBRUptLock = MACH_PORT_NULL;

finish:
    if (rval) {
        OSKextLog(NULL, kOSKextLogWarningLevel | kOSKextLogIPCFlag,
            "Couldn't unlock volume for %s: %s (%d).",
            path, safe_mach_error_string(rval), rval);
    } else {
        sBRUptLockCtr--;

        if (wasLocked && sBRUptLockCtr == 0) {
            unsetenv("_com_apple_kextd_skiplocks");
        }
    }

    return rval;
}

/*******************************************************************************
 * copy_kcsuffix() - return the current value of the kcsuffix boot-arg.
 * Caller must release the returned CFStringRef.
 *
 * The kcsuffix value tells us which prelinkedkernel file the booter should use.
 * "kcsuffix=" is the same as "kcsuffix=release" which means the booter should
 * use "prelinkedkernel" file.  Any other suffix means use "prelinkedkernel"
 * plus the given suffix with a '.' before the suffix.
 * 
 * For example:
 * "kcsuffix=development" means the booter should pick the 
 * "prelinkedkernel.development" file.
 *******************************************************************************/
CFStringRef copy_kcsuffix(void)
{
    CFStringRef         result          = NULL;
    CFStringRef         myTempStr;
    io_registry_entry_t optionsNode     = MACH_PORT_NULL;   // must release
    CFStringRef         bootargsEntry   = NULL;             // must release
    CFArrayRef          myStringArray   = NULL;             // must release
    CFRange             findRange, myRange;
    CFIndex             count, i;
    
    optionsNode = IORegistryEntryFromPath(kIOMasterPortDefault,
                                          "IODeviceTree:/options");
    while (optionsNode) {
        bootargsEntry = (CFStringRef)
        IORegistryEntryCreateCFProperty(optionsNode,
                                        CFSTR("boot-args"),
                                        kCFAllocatorDefault, 0);
        if (bootargsEntry == NULL ||
            (CFGetTypeID(bootargsEntry) != CFStringGetTypeID())) {
            break;
        }
        
        // a blank space is used to delimit the various values of boot-args
        // We are looking for something like:
        // boot-args="-v debug=0x146 kext-dev-mode=0 kcsuffix=release"
        myStringArray = CFStringCreateArrayBySeparatingStrings(
                                                               kCFAllocatorDefault,
                                                               bootargsEntry,
                                                               CFSTR(" ") );
        if (myStringArray == NULL) {
            break;
        }
        
        count = CFArrayGetCount(myStringArray);
        for (i = 0; i < count; i++) {
            CFStringRef myString = NULL;
            CFIndex     myStringLen;
            
            myString = CFArrayGetValueAtIndex(myStringArray, i);
            if (myString == NULL)  continue;
            findRange = CFStringFind(myString, CFSTR("kcsuffix="), 0);
            if (findRange.length == 0) {
                continue;
            }
            myStringLen = CFStringGetLength(myString);
            if (findRange.length == 9 && myStringLen == 9) {
                // "kcsuffix=" with no value means "release"
                result = CFRetain(CFSTR(".release"));
                break;
            }
            
            // grab suffix and return it
            myRange.length = myStringLen - 9;
            myRange.location = findRange.location + 9;
            
            myTempStr = CFStringCreateWithSubstring(kCFAllocatorDefault,
                                                    myString,
                                                    myRange);
            if (myTempStr) {
                result = CFStringCreateWithFormat(
                                                  kCFAllocatorDefault,
                                                  /* formatOptions */ NULL,
                                                  CFSTR("%s%@"),
                                                  ".",
                                                  myTempStr );
                CFRelease(myTempStr);
            }
            
            break;
        } // for ...
        break;
    } // while ...
    
    if (optionsNode)  IOObjectRelease(optionsNode);
    SAFE_RELEASE(bootargsEntry);
    SAFE_RELEASE(myStringArray);
    
    if (result == NULL) {
        // nothing set then let's default to development prelinkedkernel
        result = CFRetain(CFSTR(".development"));
    }
    
    return(result);
}