1/*- 2 * See the file LICENSE for redistribution information. 3 * 4 * Copyright (c) 1996,2008 Oracle. All rights reserved. 5 * 6 * $Id: os_fid.c,v 12.20 2008/01/08 20:58:43 bostic Exp $ 7 */ 8 9#include "db_config.h" 10 11#include "db_int.h" 12 13/* 14 * __os_fileid -- 15 * Return a unique identifier for a file. 16 * 17 * PUBLIC: int __os_fileid __P((ENV *, const char *, int, u_int8_t *)); 18 */ 19int 20__os_fileid(env, fname, unique_okay, fidp) 21 ENV *env; 22 const char *fname; 23 int unique_okay; 24 u_int8_t *fidp; 25{ 26 pid_t pid; 27 size_t i; 28 u_int32_t tmp; 29 u_int8_t *p; 30 31#ifdef HAVE_STAT 32 struct stat sb; 33 int ret; 34 35 /* 36 * The structure of a fileid on a POSIX/UNIX system is: 37 * 38 * ino[4] dev[4] unique-ID[4] serial-counter[4] empty[4]. 39 * 40 * For real files, which have a backing inode and device, the first 41 * 8 bytes are filled in and the following bytes are left 0. For 42 * temporary files, the following 12 bytes are filled in. 43 * 44 * Clear the buffer. 45 */ 46 memset(fidp, 0, DB_FILE_ID_LEN); 47 RETRY_CHK((stat(CHAR_STAR_CAST fname, &sb)), ret); 48 if (ret != 0) { 49 __db_syserr(env, ret, "stat: %s", fname); 50 return (__os_posix_err(ret)); 51 } 52 53 /* 54 * !!! 55 * Nothing is ever big enough -- on Sparc V9, st_ino, st_dev and the 56 * time_t types are all 8 bytes. As DB_FILE_ID_LEN is only 20 bytes, 57 * we convert to a (potentially) smaller fixed-size type and use it. 58 * 59 * We don't worry about byte sexing or the actual variable sizes. 60 * 61 * When this routine is called from the DB access methods, it's only 62 * called once -- whatever ID is generated when a database is created 63 * is stored in the database file's metadata, and that is what is 64 * saved in the mpool region's information to uniquely identify the 65 * file. 66 * 67 * When called from the mpool layer this routine will be called each 68 * time a new thread of control wants to share the file, which makes 69 * things tougher. As far as byte sexing goes, since the mpool region 70 * lives on a single host, there's no issue of that -- the entire 71 * region is byte sex dependent. As far as variable sizes go, we make 72 * the simplifying assumption that 32-bit and 64-bit processes will 73 * get the same 32-bit values if we truncate any returned 64-bit value 74 * to a 32-bit value. When we're called from the mpool layer, though, 75 * we need to be careful not to include anything that isn't 76 * reproducible for a given file, such as the timestamp or serial 77 * number. 78 */ 79 tmp = (u_int32_t)sb.st_ino; 80 for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) 81 *fidp++ = *p++; 82 83 tmp = (u_int32_t)sb.st_dev; 84 for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) 85 *fidp++ = *p++; 86#else 87 /* 88 * Use the file name. 89 * 90 * XXX 91 * Cast the first argument, the BREW ARM compiler is unhappy if 92 * we don't. 93 */ 94 (void)strncpy((char *)fidp, fname, DB_FILE_ID_LEN); 95#endif /* HAVE_STAT */ 96 97 if (unique_okay) { 98 /* Add in 32-bits of (hopefully) unique number. */ 99 __os_unique_id(env, &tmp); 100 for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i) 101 *fidp++ = *p++; 102 103 /* 104 * Initialize/increment the serial number we use to help 105 * avoid fileid collisions. Note we don't bother with 106 * locking; it's unpleasant to do from down in here, and 107 * if we race on this no real harm will be done, since the 108 * finished fileid has so many other components. 109 * 110 * We use the bottom 32-bits of the process ID, hoping they 111 * are more random than the top 32-bits (should we be on a 112 * machine with 64-bit process IDs). 113 * 114 * We increment by 100000 on each call as a simple way of 115 * randomizing; simply incrementing seems potentially less 116 * useful if pids are also simply incremented, since this 117 * is process-local and we may be one of a set of processes 118 * starting up. 100000 pushes us out of pid space on most 119 * 32-bit platforms, and has few interesting properties in 120 * base 2. 121 */ 122 if (DB_GLOBAL(fid_serial) == 0) { 123 __os_id(env->dbenv, &pid, NULL); 124 DB_GLOBAL(fid_serial) = (u_int32_t)pid; 125 } else 126 DB_GLOBAL(fid_serial) += 100000; 127 128 for (p = (u_int8_t *) 129 &DB_GLOBAL(fid_serial), i = sizeof(u_int32_t); i > 0; --i) 130 *fidp++ = *p++; 131 } 132 133 return (0); 134} 135