sys_pipe.c   [plain text]

/*
 * Copyright (c) 1996 John S. Dyson
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice immediately at the beginning of the file, without modification,
 *    this list of conditions, and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Absolutely no warranty of function or purpose is made by the author
 *    John S. Dyson.
 * 4. Modifications may be freely made to this file if the above conditions
 *    are met.
 */
/*
 * Copyright (c) 2003-2007 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_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. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * 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_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */

/*
 * This file contains a high-performance replacement for the socket-based
 * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
 * all features of sockets, but does do everything that pipes normally
 * do.
 *
 * Pipes are implemented as circular buffers. Following are the valid states in pipes operations
 *  
 *      _________________________________
 * 1.  |_________________________________| r=w, c=0
 * 
 *      _________________________________
 * 2.  |__r:::::wc_______________________| r <= w , c > 0
 *
 *      _________________________________
 * 3.  |::::wc_____r:::::::::::::::::::::| r>w , c > 0
 *
 *      _________________________________
 * 4.  |:::::::wrc:::::::::::::::::::::::| w=r, c = Max size
 *
 *
 *  Nomenclature:-
 *  a-z define the steps in a program flow
 *  1-4 are the states as defined aboe
 *  Action: is what file operation is done on the pipe
 *  
 *  Current:None  Action: initialize with size M=200
 *  a. State 1 ( r=0, w=0, c=0)
 *  
 *  Current: a    Action: write(100) (w < M)
 *  b. State 2 (r=0, w=100, c=100)
 *  
 *  Current: b    Action: write(100) (w = M-w)
 *  c. State 4 (r=0,w=0,c=200)
 *  
 *  Current: b    Action: read(70)  ( r < c )
 *  d. State 2(r=70,w=100,c=30)
 *  
 *  Current: d	  Action: write(75) ( w < (m-w))
 *  e. State 2 (r=70,w=175,c=105)
 *  
 *  Current: d    Action: write(110) ( w > (m-w))
 *  f. State 3 (r=70,w=10,c=140)
 *  
 *  Current: d	  Action: read(30) (r >= c )
 *  g. State 1 (r=100,w=100,c=0)
 *  
 */

/*
 * This code create half duplex pipe buffers for facilitating file like
 * operations on pipes. The initial buffer is very small, but this can
 * dynamically change to larger sizes based on usage. The buffer size is never
 * reduced. The total amount of kernel memory used is governed by maxpipekva.
 * In case of dynamic expansion limit is reached, the output thread is blocked
 * until the pipe buffer empties enough to continue. 
 *
 * In order to limit the resource use of pipes, two sysctls exist:
 *
 * kern.ipc.maxpipekva - This is a hard limit on the amount of pageable
 * address space available to us in pipe_map. 
 *
 * Memory usage may be monitored through the sysctls
 * kern.ipc.pipes, kern.ipc.pipekva.
 *
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/file_internal.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <sys/malloc.h>
#include <sys/syslog.h>
#include <sys/unistd.h>
#include <sys/resourcevar.h>
#include <sys/aio_kern.h>
#include <sys/signalvar.h>
#include <sys/pipe.h>
#include <sys/sysproto.h>
#include <sys/proc_info.h>

#include <security/audit/audit.h>

#include <sys/kdebug.h>

#include <kern/zalloc.h>
#include <kern/kalloc.h>
#include <vm/vm_kern.h>
#include <libkern/OSAtomic.h>

#define f_flag f_fglob->fg_flag
#define f_msgcount f_fglob->fg_msgcount
#define f_cred f_fglob->fg_cred
#define f_ops f_fglob->fg_ops
#define f_offset f_fglob->fg_offset
#define f_data f_fglob->fg_data

/*
 * interfaces to the outside world exported through file operations 
 */
static int pipe_read(struct fileproc *fp, struct uio *uio,
                int flags, vfs_context_t ctx);
static int pipe_write(struct fileproc *fp, struct uio *uio,
                int flags, vfs_context_t ctx);
static int pipe_close(struct fileglob *fg, vfs_context_t ctx);
static int pipe_select(struct fileproc *fp, int which, void * wql,
		vfs_context_t ctx);
static int pipe_kqfilter(struct fileproc *fp, struct knote *kn,
		vfs_context_t ctx);
static int pipe_ioctl(struct fileproc *fp, u_long cmd, caddr_t data,
		vfs_context_t ctx);
static int pipe_drain(struct fileproc *fp,vfs_context_t ctx);

static const struct fileops pipeops = {
	DTYPE_PIPE,
	pipe_read,
	pipe_write,
	pipe_ioctl,
	pipe_select,
	pipe_close,
	pipe_kqfilter,
	pipe_drain
};

static void	filt_pipedetach(struct knote *kn);
static int	filt_piperead(struct knote *kn, long hint);
static int	filt_pipewrite(struct knote *kn, long hint);

static struct filterops pipe_rfiltops = {
        .f_isfd = 1,
        .f_detach = filt_pipedetach,
        .f_event = filt_piperead,
};

static struct filterops pipe_wfiltops = {
        .f_isfd = 1,
        .f_detach = filt_pipedetach,
        .f_event = filt_pipewrite,
};

static int nbigpipe;      /* for compatibility sake. no longer used */
static int amountpipes;   /* total number of pipes in system */
static int amountpipekva; /* total memory used by pipes */

int maxpipekva __attribute__((used)) = PIPE_KVAMAX;  /* allowing 16MB max. */

#if PIPE_SYSCTLS
SYSCTL_DECL(_kern_ipc);

SYSCTL_INT(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RD|CTLFLAG_LOCKED,
	   &maxpipekva, 0, "Pipe KVA limit");
SYSCTL_INT(_kern_ipc, OID_AUTO, maxpipekvawired, CTLFLAG_RW|CTLFLAG_LOCKED,
	   &maxpipekvawired, 0, "Pipe KVA wired limit");
SYSCTL_INT(_kern_ipc, OID_AUTO, pipes, CTLFLAG_RD|CTLFLAG_LOCKED,
	   &amountpipes, 0, "Current # of pipes");
SYSCTL_INT(_kern_ipc, OID_AUTO, bigpipes, CTLFLAG_RD|CTLFLAG_LOCKED,
	   &nbigpipe, 0, "Current # of big pipes");
SYSCTL_INT(_kern_ipc, OID_AUTO, pipekva, CTLFLAG_RD|CTLFLAG_LOCKED,
	   &amountpipekva, 0, "Pipe KVA usage");
SYSCTL_INT(_kern_ipc, OID_AUTO, pipekvawired, CTLFLAG_RD|CTLFLAG_LOCKED,
	   &amountpipekvawired, 0, "Pipe wired KVA usage");
#endif

static void pipeclose(struct pipe *cpipe);
static void pipe_free_kmem(struct pipe *cpipe);
static int pipe_create(struct pipe **cpipep);
static int pipespace(struct pipe *cpipe, int size);
static int choose_pipespace(unsigned long current, unsigned long expected);
static int expand_pipespace(struct pipe *p, int target_size);
static void pipeselwakeup(struct pipe *cpipe, struct pipe *spipe);
static __inline int pipeio_lock(struct pipe *cpipe, int catch);
static __inline void pipeio_unlock(struct pipe *cpipe);

extern int postpipeevent(struct pipe *, int);
extern void evpipefree(struct pipe *cpipe);

static lck_grp_t	*pipe_mtx_grp;
static lck_attr_t	*pipe_mtx_attr;
static lck_grp_attr_t	*pipe_mtx_grp_attr;

static zone_t pipe_zone;

#define MAX_PIPESIZE(pipe)  		( MAX(PIPE_SIZE, (pipe)->pipe_buffer.size) )

#define	PIPE_GARBAGE_AGE_LIMIT		5000	/* In milliseconds */
#define PIPE_GARBAGE_QUEUE_LIMIT	32000

struct pipe_garbage {
	struct pipe		*pg_pipe;
	struct pipe_garbage	*pg_next;
	uint64_t		pg_timestamp;
};

static zone_t pipe_garbage_zone;
static struct pipe_garbage *pipe_garbage_head = NULL;
static struct pipe_garbage *pipe_garbage_tail = NULL;
static uint64_t pipe_garbage_age_limit = PIPE_GARBAGE_AGE_LIMIT;
static int pipe_garbage_count = 0;
static lck_mtx_t *pipe_garbage_lock;
static void pipe_garbage_collect(struct pipe *cpipe);

SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);

/* initial setup done at time of sysinit */
void
pipeinit(void)
{
	nbigpipe=0;
	vm_size_t zone_size;
 
	zone_size = 8192 * sizeof(struct pipe);
        pipe_zone = zinit(sizeof(struct pipe), zone_size, 4096, "pipe zone");


	/* allocate lock group attribute and group for pipe mutexes */
	pipe_mtx_grp_attr = lck_grp_attr_alloc_init();
	pipe_mtx_grp = lck_grp_alloc_init("pipe", pipe_mtx_grp_attr);

	/* allocate the lock attribute for pipe mutexes */
	pipe_mtx_attr = lck_attr_alloc_init();

	/*
	 * Set up garbage collection for dead pipes
	 */
	zone_size = (PIPE_GARBAGE_QUEUE_LIMIT + 20) *
	    sizeof(struct pipe_garbage);
        pipe_garbage_zone = (zone_t)zinit(sizeof(struct pipe_garbage),
	    zone_size, 4096, "pipe garbage zone");
	pipe_garbage_lock = lck_mtx_alloc_init(pipe_mtx_grp, pipe_mtx_attr);
	
}

/* Bitmap for things to touch in pipe_touch() */
#define	PIPE_ATIME	0x00000001	/* time of last access */
#define	PIPE_MTIME	0x00000002	/* time of last modification */
#define	PIPE_CTIME	0x00000004	/* time of last status change */

static void
pipe_touch(struct pipe *tpipe, int touch)
{
	struct timeval now;

	microtime(&now);

	if (touch & PIPE_ATIME) {
		tpipe->st_atimespec.tv_sec  = now.tv_sec;
		tpipe->st_atimespec.tv_nsec = now.tv_usec * 1000;
	}

	if (touch & PIPE_MTIME) {
		tpipe->st_mtimespec.tv_sec  = now.tv_sec;
		tpipe->st_mtimespec.tv_nsec = now.tv_usec * 1000;
	}

	if (touch & PIPE_CTIME) {
		tpipe->st_ctimespec.tv_sec  = now.tv_sec;
		tpipe->st_ctimespec.tv_nsec = now.tv_usec * 1000;
	}
}

static const unsigned int pipesize_blocks[] = {128,256,1024,2048,PAGE_SIZE, PAGE_SIZE * 2, PIPE_SIZE , PIPE_SIZE * 4 };

/* 
 * finds the right size from possible sizes in pipesize_blocks 
 * returns the size which matches max(current,expected) 
 */
static int 
choose_pipespace(unsigned long current, unsigned long expected)
{
	int i = sizeof(pipesize_blocks)/sizeof(unsigned int) -1;
	unsigned long target;

	if (expected > current) 
		target = expected;
	else
		target = current;

	while ( i >0 && pipesize_blocks[i-1] > target) {
		i=i-1;

	}
	
	return pipesize_blocks[i];
}


/*
 * expand the size of pipe while there is data to be read,
 * and then free the old buffer once the current buffered
 * data has been transferred to new storage.
 * Required: PIPE_LOCK and io lock to be held by caller.
 * returns 0 on success or no expansion possible
 */
static int 
expand_pipespace(struct pipe *p, int target_size)
{
	struct pipe tmp, oldpipe;
	int error;
	tmp.pipe_buffer.buffer = 0;
	
	if (p->pipe_buffer.size >= (unsigned) target_size) {
		return 0; /* the existing buffer is max size possible */
	}
	
	/* create enough space in the target */
	error = pipespace(&tmp, target_size);
	if (error != 0)
		return (error);

	oldpipe.pipe_buffer.buffer = p->pipe_buffer.buffer;
	oldpipe.pipe_buffer.size = p->pipe_buffer.size;
	
	memcpy(tmp.pipe_buffer.buffer, p->pipe_buffer.buffer, p->pipe_buffer.size);
	if (p->pipe_buffer.cnt > 0 && p->pipe_buffer.in <= p->pipe_buffer.out ){
		/* we are in State 3 and need extra copying for read to be consistent */
		memcpy(&tmp.pipe_buffer.buffer[p->pipe_buffer.size], p->pipe_buffer.buffer, p->pipe_buffer.size);
		p->pipe_buffer.in += p->pipe_buffer.size;
	}

	p->pipe_buffer.buffer = tmp.pipe_buffer.buffer;
	p->pipe_buffer.size = tmp.pipe_buffer.size;


	pipe_free_kmem(&oldpipe);
	return 0;
}

/*
 * The pipe system call for the DTYPE_PIPE type of pipes
 * 
 * returns:
 *  FREAD  | fd0 | -->[struct rpipe] --> |~~buffer~~| \  
 *                                                    (pipe_mutex)
 *  FWRITE | fd1 | -->[struct wpipe] --X              / 
 */

/* ARGSUSED */
int
pipe(proc_t p, __unused struct pipe_args *uap, int32_t *retval)
{
	struct fileproc *rf, *wf;
	struct pipe *rpipe, *wpipe;
	lck_mtx_t   *pmtx;
	int fd, error;

	if ((pmtx = lck_mtx_alloc_init(pipe_mtx_grp, pipe_mtx_attr)) == NULL)
	        return (ENOMEM);
	
	rpipe = wpipe = NULL;
	if (pipe_create(&rpipe) || pipe_create(&wpipe)) {
	        error = ENFILE;
		goto freepipes;
	}
        /*
	 * allocate the space for the normal I/O direction up
	 * front... we'll delay the allocation for the other
	 * direction until a write actually occurs (most likely it won't)...
         */
	error = pipespace(rpipe, choose_pipespace(rpipe->pipe_buffer.size, 0));
        if (error)
	        goto freepipes;

	TAILQ_INIT(&rpipe->pipe_evlist);
	TAILQ_INIT(&wpipe->pipe_evlist);

	error = falloc(p, &rf, &fd, vfs_context_current());
	if (error) {
	        goto freepipes;
	}
	retval[0] = fd;

	/*
	 * for now we'll create half-duplex pipes(refer returns section above). 
	 * this is what we've always supported..
	 */
	rf->f_flag = FREAD;
	rf->f_data = (caddr_t)rpipe;
	rf->f_ops = &pipeops;

	error = falloc(p, &wf, &fd, vfs_context_current());
	if (error) {
		fp_free(p, retval[0], rf);
	        goto freepipes;
	}
	wf->f_flag = FWRITE;
	wf->f_data = (caddr_t)wpipe;
	wf->f_ops = &pipeops;

	rpipe->pipe_peer = wpipe;
	wpipe->pipe_peer = rpipe;
	/* both structures share the same mutex */
	rpipe->pipe_mtxp = wpipe->pipe_mtxp = pmtx; 

	retval[1] = fd;
#if CONFIG_MACF
	/*
	 * XXXXXXXX SHOULD NOT HOLD FILE_LOCK() XXXXXXXXXXXX
	 *
	 * struct pipe represents a pipe endpoint.  The MAC label is shared
	 * between the connected endpoints.  As a result mac_pipe_label_init() and
	 * mac_pipe_label_associate() should only be called on one of the endpoints
	 * after they have been connected.
	 */
	mac_pipe_label_init(rpipe);
	mac_pipe_label_associate(kauth_cred_get(), rpipe);
	wpipe->pipe_label = rpipe->pipe_label;
#endif
	proc_fdlock_spin(p);
	procfdtbl_releasefd(p, retval[0], NULL);
	procfdtbl_releasefd(p, retval[1], NULL);
	fp_drop(p, retval[0], rf, 1);
	fp_drop(p, retval[1], wf, 1);
	proc_fdunlock(p);


	return (0);

freepipes:
	pipeclose(rpipe); 
	pipeclose(wpipe); 
	lck_mtx_free(pmtx, pipe_mtx_grp);

	return (error);
}

int
pipe_stat(struct pipe *cpipe, void *ub, int isstat64)
{
#if CONFIG_MACF
        int error;
#endif
	int	pipe_size = 0;
	int	pipe_count;
	struct stat *sb = (struct stat *)0;	/* warning avoidance ; protected by isstat64 */
	struct stat64 * sb64 = (struct stat64 *)0;  /* warning avoidance ; protected by isstat64 */

	if (cpipe == NULL)
	        return (EBADF);
	PIPE_LOCK(cpipe);

#if CONFIG_MACF
	error = mac_pipe_check_stat(kauth_cred_get(), cpipe);
	if (error) {
		PIPE_UNLOCK(cpipe);
	        return (error);
	}
#endif
	if (cpipe->pipe_buffer.buffer == 0) {
	        /* must be stat'ing the write fd */
	        if (cpipe->pipe_peer) {
		        /* the peer still exists, use it's info */
		        pipe_size  = MAX_PIPESIZE(cpipe->pipe_peer);
			pipe_count = cpipe->pipe_peer->pipe_buffer.cnt;
		} else {
			pipe_count = 0;
		}
	} else {
	        pipe_size  = MAX_PIPESIZE(cpipe);
		pipe_count = cpipe->pipe_buffer.cnt;
	}
	/*
	 * since peer's buffer is setup ouside of lock
	 * we might catch it in transient state
	 */
	if (pipe_size == 0)
		pipe_size  = MAX(PIPE_SIZE, pipesize_blocks[0]);

	if (isstat64 != 0) {
		sb64 = (struct stat64 *)ub;	

		bzero(sb64, sizeof(*sb64));
		sb64->st_mode = S_IFIFO | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
		sb64->st_blksize = pipe_size;
		sb64->st_size = pipe_count;
		sb64->st_blocks = (sb64->st_size + sb64->st_blksize - 1) / sb64->st_blksize;
	
		sb64->st_uid = kauth_getuid();
		sb64->st_gid = kauth_getgid();
	
		sb64->st_atimespec.tv_sec  = cpipe->st_atimespec.tv_sec;
		sb64->st_atimespec.tv_nsec = cpipe->st_atimespec.tv_nsec;
	
		sb64->st_mtimespec.tv_sec  = cpipe->st_mtimespec.tv_sec;
		sb64->st_mtimespec.tv_nsec = cpipe->st_mtimespec.tv_nsec;

		sb64->st_ctimespec.tv_sec  = cpipe->st_ctimespec.tv_sec;
		sb64->st_ctimespec.tv_nsec = cpipe->st_ctimespec.tv_nsec;

		/*
	 	* Return a relatively unique inode number based on the current
	 	* address of this pipe's struct pipe.  This number may be recycled
	 	* relatively quickly.
	 	*/
		sb64->st_ino = (ino64_t)VM_KERNEL_ADDRPERM((uintptr_t)cpipe);
	} else {
		sb = (struct stat *)ub;	

		bzero(sb, sizeof(*sb));
		sb->st_mode = S_IFIFO | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
		sb->st_blksize = pipe_size;
		sb->st_size = pipe_count;
		sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
	
		sb->st_uid = kauth_getuid();
		sb->st_gid = kauth_getgid();
	
		sb->st_atimespec.tv_sec  = cpipe->st_atimespec.tv_sec;
		sb->st_atimespec.tv_nsec = cpipe->st_atimespec.tv_nsec;
	
		sb->st_mtimespec.tv_sec  = cpipe->st_mtimespec.tv_sec;
		sb->st_mtimespec.tv_nsec = cpipe->st_mtimespec.tv_nsec;

		sb->st_ctimespec.tv_sec  = cpipe->st_ctimespec.tv_sec;
		sb->st_ctimespec.tv_nsec = cpipe->st_ctimespec.tv_nsec;

		/*
	 	* Return a relatively unique inode number based on the current
	 	* address of this pipe's struct pipe.  This number may be recycled
	 	* relatively quickly.
	 	*/
		sb->st_ino = (ino_t)VM_KERNEL_ADDRPERM((uintptr_t)cpipe);
	}
	PIPE_UNLOCK(cpipe);

	/*
	 * POSIX: Left as 0: st_dev, st_nlink, st_rdev, st_flags, st_gen,
	 * st_uid, st_gid.
	 *
	 * XXX (st_dev) should be unique, but there is no device driver that
	 * XXX is associated with pipes, since they are implemented via a
	 * XXX struct fileops indirection rather than as FS objects.
	 */
	return (0);
}


/*
 * Allocate kva for pipe circular buffer, the space is pageable
 * This routine will 'realloc' the size of a pipe safely, if it fails
 * it will retain the old buffer.
 * If it fails it will return ENOMEM.
 */
static int
pipespace(struct pipe *cpipe, int size)
{
	vm_offset_t buffer;

	if (size <= 0)
		return(EINVAL);

	if ((buffer = (vm_offset_t)kalloc(size)) == 0 )
		return(ENOMEM);

	/* free old resources if we're resizing */
	pipe_free_kmem(cpipe);
	cpipe->pipe_buffer.buffer = (caddr_t)buffer;
	cpipe->pipe_buffer.size = size;
	cpipe->pipe_buffer.in = 0;
	cpipe->pipe_buffer.out = 0;
	cpipe->pipe_buffer.cnt = 0;

	OSAddAtomic(1, &amountpipes);
	OSAddAtomic(cpipe->pipe_buffer.size, &amountpipekva);

	return (0);
}

/*
 * initialize and allocate VM and memory for pipe
 */
static int
pipe_create(struct pipe **cpipep)
{
	struct pipe *cpipe;
	cpipe = (struct pipe *)zalloc(pipe_zone);

	if ((*cpipep = cpipe) == NULL)
		return (ENOMEM);

	/*
	 * protect so pipespace or pipeclose don't follow a junk pointer
	 * if pipespace() fails.
	 */
	bzero(cpipe, sizeof *cpipe);

	/* Initial times are all the time of creation of the pipe */
	pipe_touch(cpipe, PIPE_ATIME | PIPE_MTIME | PIPE_CTIME);
	return (0);
}


/*
 * lock a pipe for I/O, blocking other access
 */
static inline int
pipeio_lock(struct pipe *cpipe, int catch)
{
	int error;
	while (cpipe->pipe_state & PIPE_LOCKFL) {
		cpipe->pipe_state |= PIPE_LWANT;
		error = msleep(cpipe, PIPE_MTX(cpipe), catch ? (PRIBIO | PCATCH) : PRIBIO,
			       "pipelk", 0);
		if (error != 0) 
			return (error);
	}
	cpipe->pipe_state |= PIPE_LOCKFL;
	return (0);
}

/*
 * unlock a pipe I/O lock
 */
static inline void
pipeio_unlock(struct pipe *cpipe)
{
	cpipe->pipe_state &= ~PIPE_LOCKFL;
	if (cpipe->pipe_state & PIPE_LWANT) {
		cpipe->pipe_state &= ~PIPE_LWANT;
		wakeup(cpipe);
	}
}

/*
 * wakeup anyone whos blocked in select
 */
static void
pipeselwakeup(struct pipe *cpipe, struct pipe *spipe)
{
	if (cpipe->pipe_state & PIPE_SEL) {
		cpipe->pipe_state &= ~PIPE_SEL;
		selwakeup(&cpipe->pipe_sel);
	}
        if (cpipe->pipe_state & PIPE_KNOTE) 
	       KNOTE(&cpipe->pipe_sel.si_note, 1);

	postpipeevent(cpipe, EV_RWBYTES);

	if (spipe && (spipe->pipe_state & PIPE_ASYNC) && spipe->pipe_pgid) {
	        if (spipe->pipe_pgid < 0)
		        gsignal(-spipe->pipe_pgid, SIGIO);
		else 
		        proc_signal(spipe->pipe_pgid, SIGIO);
        }
}

/*
 * Read n bytes from the buffer. Semantics are similar to file read.
 * returns: number of bytes read from the buffer
 */
/* ARGSUSED */
static int
pipe_read(struct fileproc *fp, struct uio *uio, __unused int flags,
	__unused vfs_context_t ctx)
{
	struct pipe *rpipe = (struct pipe *)fp->f_data;
	int error;
	int nread = 0;
	u_int size;

	PIPE_LOCK(rpipe);
	++rpipe->pipe_busy;

	error = pipeio_lock(rpipe, 1);
	if (error)
		goto unlocked_error;

#if CONFIG_MACF
	error = mac_pipe_check_read(kauth_cred_get(), rpipe);
	if (error)
		goto locked_error;
#endif


	while (uio_resid(uio)) {
		/*
		 * normal pipe buffer receive
		 */
		if (rpipe->pipe_buffer.cnt > 0) {
			/*
			 * # bytes to read is min( bytes from read pointer until end of buffer,
			 *                         total unread bytes, 
			 *                         user requested byte count)
			 */
			size = rpipe->pipe_buffer.size - rpipe->pipe_buffer.out;
			if (size > rpipe->pipe_buffer.cnt)
				size = rpipe->pipe_buffer.cnt;
			// LP64todo - fix this!
			if (size > (u_int) uio_resid(uio))
				size = (u_int) uio_resid(uio);

			PIPE_UNLOCK(rpipe); /* we still hold io lock.*/
			error = uiomove(
			    &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
			    size, uio);
			PIPE_LOCK(rpipe);
			if (error)
				break;

			rpipe->pipe_buffer.out += size;
			if (rpipe->pipe_buffer.out >= rpipe->pipe_buffer.size)
				rpipe->pipe_buffer.out = 0;

			rpipe->pipe_buffer.cnt -= size;
			
			/*
			 * If there is no more to read in the pipe, reset
			 * its pointers to the beginning.  This improves
			 * cache hit stats.
			 */
			if (rpipe->pipe_buffer.cnt == 0) {
				rpipe->pipe_buffer.in = 0;
				rpipe->pipe_buffer.out = 0;
			}
			nread += size;
		} else {
			/*
			 * detect EOF condition
			 * read returns 0 on EOF, no need to set error
			 */
			if (rpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF)) {
				break;
			}

			/*
			 * If the "write-side" has been blocked, wake it up now.
			 */
			if (rpipe->pipe_state & PIPE_WANTW) {
				rpipe->pipe_state &= ~PIPE_WANTW;
				wakeup(rpipe);
			}

			/*
			 * Break if some data was read in previous iteration.
			 */
			if (nread > 0)
				break;

			/*
			 * Unlock the pipe buffer for our remaining processing. 
			 * We will either break out with an error or we will
			 * sleep and relock to loop.
			 */
			pipeio_unlock(rpipe);

			/*
			 * Handle non-blocking mode operation or
			 * wait for more data.
			 */
			if (fp->f_flag & FNONBLOCK) {
				error = EAGAIN;
			} else {
				rpipe->pipe_state |= PIPE_WANTR;
				error = msleep(rpipe, PIPE_MTX(rpipe), PRIBIO | PCATCH, "piperd", 0);
				if (error == 0)
				        error = pipeio_lock(rpipe, 1);
			}
			if (error)
				goto unlocked_error;
		}
	}
#if CONFIG_MACF
locked_error:
#endif
	pipeio_unlock(rpipe);

unlocked_error:
	--rpipe->pipe_busy;

	/*
	 * PIPE_WANT processing only makes sense if pipe_busy is 0.
	 */
	if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
		rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
		wakeup(rpipe);
	} else if (rpipe->pipe_buffer.cnt < rpipe->pipe_buffer.size) {
		/*
		 * Handle write blocking hysteresis.
		 */
		if (rpipe->pipe_state & PIPE_WANTW) {
			rpipe->pipe_state &= ~PIPE_WANTW;
			wakeup(rpipe);
		}
	}

	if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) > 0)
		pipeselwakeup(rpipe, rpipe->pipe_peer);

	/* update last read time */
	pipe_touch(rpipe, PIPE_ATIME);

	PIPE_UNLOCK(rpipe);

	return (error);
}

/*
 * perform a write of n bytes into the read side of buffer. Since 
 * pipes are unidirectional a write is meant to be read by the otherside only.
 */
static int
pipe_write(struct fileproc *fp, struct uio *uio, __unused int flags,
	__unused vfs_context_t ctx)
{
	int error = 0;
	int orig_resid;
	int pipe_size;
	struct pipe *wpipe, *rpipe;
	// LP64todo - fix this!
	orig_resid = uio_resid(uio);
	int space;

	rpipe = (struct pipe *)fp->f_data;

	PIPE_LOCK(rpipe);
	wpipe = rpipe->pipe_peer;

	/*
	 * detect loss of pipe read side, issue SIGPIPE if lost.
	 */
	if (wpipe == NULL || (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF))) {
		PIPE_UNLOCK(rpipe);
		return (EPIPE);
	}
#if CONFIG_MACF
	error = mac_pipe_check_write(kauth_cred_get(), wpipe);
	if (error) {
		PIPE_UNLOCK(rpipe);
		return (error);
	}
#endif
	++wpipe->pipe_busy;

	pipe_size = 0;

	/*
	 * need to allocate some storage... we delay the allocation
	 * until the first write on fd[0] to avoid allocating storage for both
	 * 'pipe ends'... most pipes are half-duplex with the writes targeting
	 * fd[1], so allocating space for both ends is a waste...
	 */

	if ( wpipe->pipe_buffer.buffer == 0 || ( 
		(unsigned)orig_resid > wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt &&
		amountpipekva < maxpipekva ) ) {

	        pipe_size = choose_pipespace(wpipe->pipe_buffer.size, wpipe->pipe_buffer.cnt + orig_resid);
	}
	if (pipe_size) {
	        /*
		 * need to do initial allocation or resizing of pipe
		 * holding both structure and io locks. 
		 */
		if ((error = pipeio_lock(wpipe, 1)) == 0) {
			if (wpipe->pipe_buffer.cnt == 0) 			
				error = pipespace(wpipe, pipe_size);
			else 
				error = expand_pipespace(wpipe, pipe_size);
		
			pipeio_unlock(wpipe);
			
			/* allocation failed */
			if (wpipe->pipe_buffer.buffer == 0)
			        error = ENOMEM;
		}
		if (error) {
		        /*
			 * If an error occurred unbusy and return, waking up any pending
			 * readers.
			 */
		        --wpipe->pipe_busy;
			if ((wpipe->pipe_busy == 0) && 
			    (wpipe->pipe_state & PIPE_WANT)) {
			        wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
				wakeup(wpipe);
			}
			PIPE_UNLOCK(rpipe);
			return(error);
		}
	}

	while (uio_resid(uio)) {

	retrywrite:
		space = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;

		/* Writes of size <= PIPE_BUF must be atomic. */
		if ((space < uio_resid(uio)) && (orig_resid <= PIPE_BUF))
			space = 0;

		if (space > 0) {

			if ((error = pipeio_lock(wpipe,1)) == 0) {
				int size;	/* Transfer size */
				int segsize;	/* first segment to transfer */

				if (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF)) {
					pipeio_unlock(wpipe);
				        error = EPIPE;
					break;
				}
				/* 
				 * If a process blocked in pipeio_lock, our
				 * value for space might be bad... the mutex
				 * is dropped while we're blocked
				 */
				if (space > (int)(wpipe->pipe_buffer.size - 
				    wpipe->pipe_buffer.cnt)) {
					pipeio_unlock(wpipe);
					goto retrywrite;
				}

				/*
				 * Transfer size is minimum of uio transfer
				 * and free space in pipe buffer.
				 */
				// LP64todo - fix this!
				if (space > uio_resid(uio))
					size = uio_resid(uio);
				else
					size = space;
				/*
				 * First segment to transfer is minimum of 
				 * transfer size and contiguous space in
				 * pipe buffer.  If first segment to transfer
				 * is less than the transfer size, we've got
				 * a wraparound in the buffer.
				 */
				segsize = wpipe->pipe_buffer.size - 
					wpipe->pipe_buffer.in;
				if (segsize > size)
					segsize = size;
				
				/* Transfer first segment */

				PIPE_UNLOCK(rpipe);
				error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in], 
						segsize, uio);
				PIPE_LOCK(rpipe);
				
				if (error == 0 && segsize < size) {
					/* 
					 * Transfer remaining part now, to
					 * support atomic writes.  Wraparound
					 * happened. (State 3)
					 */
					if (wpipe->pipe_buffer.in + segsize != 
					    wpipe->pipe_buffer.size)
						panic("Expected pipe buffer "
						    "wraparound disappeared");
						
					PIPE_UNLOCK(rpipe);
					error = uiomove(
					    &wpipe->pipe_buffer.buffer[0],
				    	    size - segsize, uio);
					PIPE_LOCK(rpipe);
				}
				/* 
				 * readers never know to read until count is updated.
				 */
				if (error == 0) {
					wpipe->pipe_buffer.in += size;
					if (wpipe->pipe_buffer.in >
					    wpipe->pipe_buffer.size) {
						if (wpipe->pipe_buffer.in !=
						    size - segsize +
						    wpipe->pipe_buffer.size)
							panic("Expected "
							    "wraparound bad");
						wpipe->pipe_buffer.in = size -
						    segsize;
					}
				
					wpipe->pipe_buffer.cnt += size;
					if (wpipe->pipe_buffer.cnt >
					    wpipe->pipe_buffer.size)
						panic("Pipe buffer overflow");
				
				}
				pipeio_unlock(wpipe);
			}
			if (error)
				break;

		} else {
			/*
			 * If the "read-side" has been blocked, wake it up now.
			 */
			if (wpipe->pipe_state & PIPE_WANTR) {
				wpipe->pipe_state &= ~PIPE_WANTR;
				wakeup(wpipe);
			}
			/*
			 * don't block on non-blocking I/O
			 * we'll do the pipeselwakeup on the way out
			 */
			if (fp->f_flag & FNONBLOCK) {
				error = EAGAIN;
				break;
			}

			/*
			 * If read side wants to go away, we just issue a signal
			 * to ourselves.
			 */
			if (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF)) {
				error = EPIPE;
				break;
			}	

			/*
			 * We have no more space and have something to offer,
			 * wake up select/poll.
			 */
			pipeselwakeup(wpipe, wpipe);

			wpipe->pipe_state |= PIPE_WANTW;

			error = msleep(wpipe, PIPE_MTX(wpipe), PRIBIO | PCATCH, "pipewr", 0);

			if (error != 0)
				break;
		}
	}
	--wpipe->pipe_busy;

	if ((wpipe->pipe_busy == 0) && (wpipe->pipe_state & PIPE_WANT)) {
		wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
		wakeup(wpipe);
	}
	if (wpipe->pipe_buffer.cnt > 0) {
		/*
		 * If there are any characters in the buffer, we wake up
		 * the reader if it was blocked waiting for data.
		 */
		if (wpipe->pipe_state & PIPE_WANTR) {
			wpipe->pipe_state &= ~PIPE_WANTR;
			wakeup(wpipe);
		}
		/*
		 * wake up thread blocked in select/poll or post the notification
		 */
		pipeselwakeup(wpipe, wpipe);
	}

	/* Update modification, status change (# of bytes in pipe) times */
	pipe_touch(rpipe, PIPE_MTIME | PIPE_CTIME);
	pipe_touch(wpipe, PIPE_MTIME | PIPE_CTIME);
	PIPE_UNLOCK(rpipe);

	return (error);
}

/*
 * we implement a very minimal set of ioctls for compatibility with sockets.
 */
/* ARGSUSED 3 */
static int
pipe_ioctl(struct fileproc *fp, u_long cmd, caddr_t data,
	__unused vfs_context_t ctx)
{
	struct pipe *mpipe = (struct pipe *)fp->f_data;
#if CONFIG_MACF
	int error;
#endif

	PIPE_LOCK(mpipe);

#if CONFIG_MACF
	error = mac_pipe_check_ioctl(kauth_cred_get(), mpipe, cmd);
	if (error) {
		PIPE_UNLOCK(mpipe);

		return (error);
	}
#endif

	switch (cmd) {

	case FIONBIO:
		PIPE_UNLOCK(mpipe);
		return (0);

	case FIOASYNC:
		if (*(int *)data) {
			mpipe->pipe_state |= PIPE_ASYNC;
		} else {
			mpipe->pipe_state &= ~PIPE_ASYNC;
		}
		PIPE_UNLOCK(mpipe);
		return (0);

	case FIONREAD:
		*(int *)data = mpipe->pipe_buffer.cnt;
		PIPE_UNLOCK(mpipe);
		return (0);

	case TIOCSPGRP:
		mpipe->pipe_pgid = *(int *)data;

		PIPE_UNLOCK(mpipe);
		return (0);

	case TIOCGPGRP:
		*(int *)data = mpipe->pipe_pgid;

		PIPE_UNLOCK(mpipe);
		return (0);

	}
	PIPE_UNLOCK(mpipe);
	return (ENOTTY);
}


static int
pipe_select(struct fileproc *fp, int which, void *wql, vfs_context_t ctx)
{
	struct pipe *rpipe = (struct pipe *)fp->f_data;
	struct pipe *wpipe;
	int    retnum = 0;

	if (rpipe == NULL || rpipe == (struct pipe *)-1)
	        return (retnum);

	PIPE_LOCK(rpipe);

	wpipe = rpipe->pipe_peer;
	

#if CONFIG_MACF
	/*
	 * XXX We should use a per thread credential here; minimally, the
	 * XXX process credential should have a persistent reference on it
	 * XXX before being passed in here.
	 */
	if (mac_pipe_check_select(vfs_context_ucred(ctx), rpipe, which)) {
		PIPE_UNLOCK(rpipe);
		return (0);
	}
#endif
        switch (which) {

        case FREAD:
		if ((rpipe->pipe_state & PIPE_DIRECTW) ||
		    (rpipe->pipe_buffer.cnt > 0) ||
		    (rpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF))) {

		        retnum = 1;
		} else {
		        rpipe->pipe_state |= PIPE_SEL;
		        selrecord(vfs_context_proc(ctx), &rpipe->pipe_sel, wql);
		}
		break;

        case FWRITE:
		if (wpipe)
			wpipe->pipe_state |= PIPE_WSELECT;
		if (wpipe == NULL || (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF)) ||
		    (((wpipe->pipe_state & PIPE_DIRECTW) == 0) &&
		     (MAX_PIPESIZE(wpipe) - wpipe->pipe_buffer.cnt) > 0)) {

		        retnum = 1;
		} else {
		        wpipe->pipe_state |= PIPE_SEL;
			selrecord(vfs_context_proc(ctx), &wpipe->pipe_sel, wql);
		}
		break;
        case 0:
	        rpipe->pipe_state |= PIPE_SEL;
		selrecord(vfs_context_proc(ctx), &rpipe->pipe_sel, wql);
		break;
        }
	PIPE_UNLOCK(rpipe);

        return (retnum);
}


/* ARGSUSED 1 */
static int
pipe_close(struct fileglob *fg, __unused vfs_context_t ctx)
{
        struct pipe *cpipe;

	proc_fdlock_spin(vfs_context_proc(ctx));
	cpipe = (struct pipe *)fg->fg_data;
	fg->fg_data = NULL;
	proc_fdunlock(vfs_context_proc(ctx));
	if (cpipe)
	        pipeclose(cpipe);

	return (0);
}

static void
pipe_free_kmem(struct pipe *cpipe)
{
	if (cpipe->pipe_buffer.buffer != NULL) {
		OSAddAtomic(-(cpipe->pipe_buffer.size), &amountpipekva);
		OSAddAtomic(-1, &amountpipes);
		kfree((void *)cpipe->pipe_buffer.buffer,
			  cpipe->pipe_buffer.size);
		cpipe->pipe_buffer.buffer = NULL;
		cpipe->pipe_buffer.size = 0;
	}
}

/*
 * shutdown the pipe
 */
static void
pipeclose(struct pipe *cpipe)
{
	struct pipe *ppipe;

	if (cpipe == NULL)
		return;
	/* partially created pipes won't have a valid mutex. */
	if (PIPE_MTX(cpipe) != NULL)
		PIPE_LOCK(cpipe);
		

	/*
	 * If the other side is blocked, wake it up saying that
	 * we want to close it down.
	 */
	cpipe->pipe_state &= ~PIPE_DRAIN;
	cpipe->pipe_state |= PIPE_EOF;
	pipeselwakeup(cpipe, cpipe);
	
	while (cpipe->pipe_busy) {
		cpipe->pipe_state |= PIPE_WANT;

		wakeup(cpipe);
 		msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
	}

#if CONFIG_MACF
	/*
	 * Free the shared pipe label only after the two ends are disconnected.
	 */
	if (cpipe->pipe_label != NULL && cpipe->pipe_peer == NULL)
		mac_pipe_label_destroy(cpipe);
#endif

	/*
	 * Disconnect from peer
	 */
	if ((ppipe = cpipe->pipe_peer) != NULL) {

		ppipe->pipe_state &= ~(PIPE_DRAIN);
		ppipe->pipe_state |= PIPE_EOF;

		pipeselwakeup(ppipe, ppipe);
		wakeup(ppipe);

		if (cpipe->pipe_state & PIPE_KNOTE)
		        KNOTE(&ppipe->pipe_sel.si_note, 1);

		postpipeevent(ppipe, EV_RCLOSED);

		ppipe->pipe_peer = NULL;
	}
	evpipefree(cpipe);

	/*
	 * free resources
	 */
	if (PIPE_MTX(cpipe) != NULL) {
		if (ppipe != NULL) {
			/*
			 * since the mutex is shared and the peer is still
			 * alive, we need to release the mutex, not free it
			 */
			PIPE_UNLOCK(cpipe);
		} else {
			/*
			 * peer is gone, so we're the sole party left with
			 * interest in this mutex... unlock and free it
			 */
			PIPE_UNLOCK(cpipe);
			lck_mtx_free(PIPE_MTX(cpipe), pipe_mtx_grp);
		}
	}
	pipe_free_kmem(cpipe);
	if (cpipe->pipe_state & PIPE_WSELECT) {
		pipe_garbage_collect(cpipe);
	} else {
		zfree(pipe_zone, cpipe);
		pipe_garbage_collect(NULL);
	}

}

/*ARGSUSED*/
static int
pipe_kqfilter(__unused struct fileproc *fp, struct knote *kn, __unused vfs_context_t ctx)
{
	struct pipe *cpipe;

	cpipe = (struct pipe *)kn->kn_fp->f_data;

	PIPE_LOCK(cpipe);
#if CONFIG_MACF
	/*
	 * XXX We should use a per thread credential here; minimally, the
	 * XXX process credential should have a persistent reference on it
	 * XXX before being passed in here.
	 */
	if (mac_pipe_check_kqfilter(vfs_context_ucred(ctx), kn, cpipe) != 0) {
		PIPE_UNLOCK(cpipe);
		return (1);
	}
#endif

	switch (kn->kn_filter) {
	case EVFILT_READ:
		kn->kn_fop = &pipe_rfiltops;

		break;
	case EVFILT_WRITE:
		kn->kn_fop = &pipe_wfiltops;

		if (cpipe->pipe_peer == NULL) {
			/*
			 * other end of pipe has been closed
			 */
		        PIPE_UNLOCK(cpipe);
			return (EPIPE);
		}
		if (cpipe->pipe_peer)
		cpipe = cpipe->pipe_peer;
		break;
	default:
	        PIPE_UNLOCK(cpipe);
		return (1);
	}

	if (KNOTE_ATTACH(&cpipe->pipe_sel.si_note, kn))
	        cpipe->pipe_state |= PIPE_KNOTE;

	PIPE_UNLOCK(cpipe);
	return (0);
}

static void
filt_pipedetach(struct knote *kn)
{
	struct pipe *cpipe = (struct pipe *)kn->kn_fp->f_data;

	PIPE_LOCK(cpipe);

	if (kn->kn_filter == EVFILT_WRITE) {
	        if (cpipe->pipe_peer == NULL) {
		        PIPE_UNLOCK(cpipe);
			return;
		}
		cpipe = cpipe->pipe_peer;
	}
	if (cpipe->pipe_state & PIPE_KNOTE) {
	        if (KNOTE_DETACH(&cpipe->pipe_sel.si_note, kn))
		        cpipe->pipe_state &= ~PIPE_KNOTE;
	}
	PIPE_UNLOCK(cpipe);
}

/*ARGSUSED*/
static int
filt_piperead(struct knote *kn, long hint)
{
	struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
	struct pipe *wpipe;
	int    retval;

	/*
	 * if hint == 0, then we've been called from the kevent
	 * world directly and do not currently hold the pipe mutex...
	 * if hint == 1, we're being called back via the KNOTE post
	 * we made in pipeselwakeup, and we already hold the mutex...
	 */
	if (hint == 0)
	        PIPE_LOCK(rpipe);

	wpipe = rpipe->pipe_peer;
	kn->kn_data = rpipe->pipe_buffer.cnt;
	if ((rpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF)) ||
	    (wpipe == NULL) || (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF))) {
		kn->kn_flags |= EV_EOF;
		retval = 1;
	} else {
		int64_t lowwat = 1;
		if (kn->kn_sfflags & NOTE_LOWAT) {
			if (rpipe->pipe_buffer.size && kn->kn_sdata > MAX_PIPESIZE(rpipe))
				lowwat = MAX_PIPESIZE(rpipe);
			else if (kn->kn_sdata > lowwat)
				lowwat = kn->kn_sdata;
		}
		retval = kn->kn_data >= lowwat;
	}

	if (hint == 0)
	        PIPE_UNLOCK(rpipe);

	return (retval);
}

/*ARGSUSED*/
static int
filt_pipewrite(struct knote *kn, long hint)
{
	struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
	struct pipe *wpipe;

	/*
	 * if hint == 0, then we've been called from the kevent
	 * world directly and do not currently hold the pipe mutex...
	 * if hint == 1, we're being called back via the KNOTE post
	 * we made in pipeselwakeup, and we already hold the mutex...
	 */
	if (hint == 0)
	        PIPE_LOCK(rpipe);

	wpipe = rpipe->pipe_peer;

	if ((wpipe == NULL) || (wpipe->pipe_state & (PIPE_DRAIN | PIPE_EOF))) {
		kn->kn_data = 0;
		kn->kn_flags |= EV_EOF; 

		if (hint == 0)
		        PIPE_UNLOCK(rpipe);
		return (1);
	}
	kn->kn_data = MAX_PIPESIZE(wpipe) - wpipe->pipe_buffer.cnt;

	int64_t lowwat = PIPE_BUF;
	if (kn->kn_sfflags & NOTE_LOWAT) {
		if (wpipe->pipe_buffer.size && kn->kn_sdata > MAX_PIPESIZE(wpipe))
			lowwat = MAX_PIPESIZE(wpipe);
		else if (kn->kn_sdata > lowwat)
			lowwat = kn->kn_sdata;
	}
	
	if (hint == 0)
	        PIPE_UNLOCK(rpipe);

	return (kn->kn_data >= lowwat);
}

int
fill_pipeinfo(struct pipe * cpipe, struct pipe_info * pinfo)
{
#if CONFIG_MACF
        int error;
#endif
	struct timeval now;
	struct vinfo_stat * ub;
	int pipe_size = 0;
	int pipe_count;

	if (cpipe == NULL)
	        return (EBADF);
	PIPE_LOCK(cpipe);

#if CONFIG_MACF
	error = mac_pipe_check_stat(kauth_cred_get(), cpipe);
	if (error) {
		PIPE_UNLOCK(cpipe);
	        return (error);
	}
#endif
	if (cpipe->pipe_buffer.buffer == 0) {
	        /*
		 * must be stat'ing the write fd
		 */
	        if (cpipe->pipe_peer) {
		        /*
			 * the peer still exists, use it's info
			 */
		        pipe_size  = MAX_PIPESIZE(cpipe->pipe_peer);
			pipe_count = cpipe->pipe_peer->pipe_buffer.cnt;
		} else {
			pipe_count = 0;
		}
	} else {
	        pipe_size  = MAX_PIPESIZE(cpipe);
		pipe_count = cpipe->pipe_buffer.cnt;
	}
	/*
	 * since peer's buffer is setup ouside of lock
	 * we might catch it in transient state
	 */
	if (pipe_size == 0)
		pipe_size  = PIPE_SIZE;

	ub = &pinfo->pipe_stat;

	bzero(ub, sizeof(*ub));
	ub->vst_mode = S_IFIFO | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
	ub->vst_blksize = pipe_size;
	ub->vst_size = pipe_count;
	if (ub->vst_blksize != 0)
		ub->vst_blocks = (ub->vst_size + ub->vst_blksize - 1) / ub->vst_blksize;
	ub->vst_nlink = 1;

	ub->vst_uid = kauth_getuid();
	ub->vst_gid = kauth_getgid();

	microtime(&now);
	ub->vst_atime  = now.tv_sec;
	ub->vst_atimensec = now.tv_usec * 1000;

	ub->vst_mtime  = now.tv_sec;
	ub->vst_mtimensec = now.tv_usec * 1000;

	ub->vst_ctime  = now.tv_sec;
	ub->vst_ctimensec = now.tv_usec * 1000;

	/*
	 * Left as 0: st_dev, st_ino, st_nlink, st_rdev, st_flags, st_gen, st_uid, st_gid.
	 * XXX (st_dev, st_ino) should be unique.
	 */

	pinfo->pipe_handle = (uint64_t)VM_KERNEL_ADDRPERM((uintptr_t)cpipe);
	pinfo->pipe_peerhandle = (uint64_t)VM_KERNEL_ADDRPERM((uintptr_t)(cpipe->pipe_peer));
	pinfo->pipe_status = cpipe->pipe_state;

	PIPE_UNLOCK(cpipe);

	return (0);
}


static int 
pipe_drain(struct fileproc *fp, __unused vfs_context_t ctx)
{

	/* Note: fdlock already held */
	struct pipe *ppipe, *cpipe = (struct pipe *)(fp->f_fglob->fg_data);

	if (cpipe) {
		PIPE_LOCK(cpipe);
		cpipe->pipe_state |= PIPE_DRAIN; 
		cpipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
		wakeup(cpipe);
		
		/* Must wake up peer: a writer sleeps on the read side */
		if ((ppipe = cpipe->pipe_peer)) {
			ppipe->pipe_state |= PIPE_DRAIN;
			ppipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
			wakeup(ppipe);
		}
		
		PIPE_UNLOCK(cpipe);
		return 0;
	}

	return 1;
}


 /*
 * When a thread sets a write-select on a pipe, it creates an implicit,
 * untracked dependency between that thread and the peer of the pipe
 * on which the select is set.  If the peer pipe is closed and freed
 * before the select()ing thread wakes up, the system will panic as
 * it attempts to unwind the dangling select().  To avoid that panic,
 * we notice whenever a dangerous select() is set on a pipe, and
 * defer the final deletion of the pipe until that select()s are all
 * resolved.  Since we can't currently detect exactly when that
 * resolution happens, we use a simple garbage collection queue to 
 * reap the at-risk pipes 'later'.
 */
static void
pipe_garbage_collect(struct pipe *cpipe)
{
	uint64_t old, now;
	struct pipe_garbage *pgp;

	/* Convert msecs to nsecs and then to abstime */
	old = pipe_garbage_age_limit * 1000000;
	nanoseconds_to_absolutetime(old, &old);

	lck_mtx_lock(pipe_garbage_lock);

	/* Free anything that's been on the queue for <mumble> seconds */
	now = mach_absolute_time();
	old = now - old;
	while ((pgp = pipe_garbage_head) && pgp->pg_timestamp < old) {
		pipe_garbage_head = pgp->pg_next;
		if (pipe_garbage_head == NULL)
			pipe_garbage_tail = NULL;
		pipe_garbage_count--;
		zfree(pipe_zone, pgp->pg_pipe);
		zfree(pipe_garbage_zone, pgp);
	}

	/* Add the new pipe (if any) to the tail of the garbage queue */
	if (cpipe) {
		cpipe->pipe_state = PIPE_DEAD;
		pgp = (struct pipe_garbage *)zalloc(pipe_garbage_zone);
		if (pgp == NULL) {
			/*
			 * We're too low on memory to garbage collect the
			 * pipe.  Freeing it runs the risk of panicing the
			 * system.  All we can do is leak it and leave
			 * a breadcrumb behind.  The good news, such as it
			 * is, is that this will probably never happen.
			 * We will probably hit the panic below first.
			 */
			printf("Leaking pipe %p - no room left in the queue",
			    cpipe);
			lck_mtx_unlock(pipe_garbage_lock);
			return;
		}

		pgp->pg_pipe = cpipe;
		pgp->pg_timestamp = now;
		pgp->pg_next = NULL;

		if (pipe_garbage_tail)
			pipe_garbage_tail->pg_next = pgp;
		pipe_garbage_tail = pgp;
		if (pipe_garbage_head == NULL)
			pipe_garbage_head = pipe_garbage_tail;

		if (pipe_garbage_count++ >= PIPE_GARBAGE_QUEUE_LIMIT)
			panic("Length of pipe garbage queue exceeded %d",
			    PIPE_GARBAGE_QUEUE_LIMIT);
	}
	lck_mtx_unlock(pipe_garbage_lock);
}