/*- * See the file LICENSE for redistribution information. * * Copyright (c) 1996,2007 Oracle. All rights reserved. * * $Id: os_fid.c,v 12.16 2007/05/17 15:15:49 bostic Exp $ */ #include "db_config.h" #include "db_int.h" /* * __os_fileid -- * Return a unique identifier for a file. */ int __os_fileid(dbenv, fname, unique_okay, fidp) DB_ENV *dbenv; const char *fname; int unique_okay; u_int8_t *fidp; { pid_t pid; size_t i; u_int32_t tmp; u_int8_t *p; int ret; /* * The documentation for GetFileInformationByHandle() states that the * inode-type numbers are not constant between processes. Actually, * they are, they're the NTFS MFT indexes. So, this works on NTFS, * but perhaps not on other platforms, and perhaps not over a network. * Can't think of a better solution right now. */ DB_FH *fhp; BY_HANDLE_FILE_INFORMATION fi; BOOL retval = FALSE; DB_ASSERT(dbenv, fname != NULL); /* Clear the buffer. */ memset(fidp, 0, DB_FILE_ID_LEN); /* * First we open the file, because we're not given a handle to it. * If we can't open it, we're in trouble. */ if ((ret = __os_open(dbenv, fname, 0, DB_OSO_RDONLY, __db_omode("r--------"), &fhp)) != 0) return (ret); /* File open, get its info */ if ((retval = GetFileInformationByHandle(fhp->handle, &fi)) == FALSE) ret = __os_get_syserr(); (void)__os_closehandle(dbenv, fhp); if (retval == FALSE) return (__os_posix_err(ret)); /* * We want the three 32-bit words which tell us the volume ID and * the file ID. We make a crude attempt to copy the bytes over to * the callers buffer. * * We don't worry about byte sexing or the actual variable sizes. * * When this routine is called from the DB access methods, it's only * called once -- whatever ID is generated when a database is created * is stored in the database file's metadata, and that is what is * saved in the mpool region's information to uniquely identify the * file. * * When called from the mpool layer this routine will be called each * time a new thread of control wants to share the file, which makes * things tougher. As far as byte sexing goes, since the mpool region * lives on a single host, there's no issue of that -- the entire * region is byte sex dependent. As far as variable sizes go, we make * the simplifying assumption that 32-bit and 64-bit processes will * get the same 32-bit values if we truncate any returned 64-bit value * to a 32-bit value. */ tmp = (u_int32_t)fi.nFileIndexLow; for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) *fidp++ = *p++; tmp = (u_int32_t)fi.nFileIndexHigh; for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) *fidp++ = *p++; if (unique_okay) { /* Add in 32-bits of (hopefully) unique number. */ __os_unique_id(dbenv, &tmp); for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) *fidp++ = *p++; /* * Initialize/increment the serial number we use to help * avoid fileid collisions. Note we don't bother with * locking; it's unpleasant to do from down in here, and * if we race on this no real harm will be done, since the * finished fileid has so many other components. * * We use the bottom 32-bits of the process ID, hoping they * are more random than the top 32-bits (should we be on a * machine with 64-bit process IDs). * * We increment by 100000 on each call as a simple way of * randomizing; simply incrementing seems potentially less * useful if pids are also simply incremented, since this * is process-local and we may be one of a set of processes * starting up. 100000 pushes us out of pid space on most * 32-bit platforms, and has few interesting properties in * base 2. */ if (DB_GLOBAL(fid_serial) == 0) { __os_id(dbenv, &pid, NULL); DB_GLOBAL(fid_serial) = (u_int32_t)pid; } else DB_GLOBAL(fid_serial) += 100000; } else { tmp = (u_int32_t)fi.dwVolumeSerialNumber; for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) *fidp++ = *p++; } return (0); }