135 lines
4.1 KiB
C
135 lines
4.1 KiB
C
/*-
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* See the file LICENSE for redistribution information.
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*
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* Copyright (c) 1996,2008 Oracle. All rights reserved.
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*
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* $Id: os_fid.c 63573 2008-05-23 21:43:21Z trent.nelson $
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*/
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#include "db_config.h"
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#include "db_int.h"
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/*
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* __os_fileid --
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* Return a unique identifier for a file.
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*
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* PUBLIC: int __os_fileid __P((ENV *, const char *, int, u_int8_t *));
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*/
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int
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__os_fileid(env, fname, unique_okay, fidp)
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ENV *env;
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const char *fname;
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int unique_okay;
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u_int8_t *fidp;
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{
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pid_t pid;
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size_t i;
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u_int32_t tmp;
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u_int8_t *p;
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#ifdef HAVE_STAT
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struct stat sb;
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int ret;
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/*
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* The structure of a fileid on a POSIX/UNIX system is:
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*
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* ino[4] dev[4] unique-ID[4] serial-counter[4] empty[4].
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*
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* For real files, which have a backing inode and device, the first
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* 8 bytes are filled in and the following bytes are left 0. For
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* temporary files, the following 12 bytes are filled in.
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*
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* Clear the buffer.
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*/
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memset(fidp, 0, DB_FILE_ID_LEN);
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RETRY_CHK((stat(CHAR_STAR_CAST fname, &sb)), ret);
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if (ret != 0) {
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__db_syserr(env, ret, "stat: %s", fname);
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return (__os_posix_err(ret));
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}
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/*
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* !!!
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* Nothing is ever big enough -- on Sparc V9, st_ino, st_dev and the
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* time_t types are all 8 bytes. As DB_FILE_ID_LEN is only 20 bytes,
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* we convert to a (potentially) smaller fixed-size type and use it.
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*
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* We don't worry about byte sexing or the actual variable sizes.
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*
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* When this routine is called from the DB access methods, it's only
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* called once -- whatever ID is generated when a database is created
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* is stored in the database file's metadata, and that is what is
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* saved in the mpool region's information to uniquely identify the
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* file.
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*
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* When called from the mpool layer this routine will be called each
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* time a new thread of control wants to share the file, which makes
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* things tougher. As far as byte sexing goes, since the mpool region
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* lives on a single host, there's no issue of that -- the entire
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* region is byte sex dependent. As far as variable sizes go, we make
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* the simplifying assumption that 32-bit and 64-bit processes will
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* get the same 32-bit values if we truncate any returned 64-bit value
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* to a 32-bit value. When we're called from the mpool layer, though,
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* we need to be careful not to include anything that isn't
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* reproducible for a given file, such as the timestamp or serial
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* number.
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*/
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tmp = (u_int32_t)sb.st_ino;
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for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
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*fidp++ = *p++;
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tmp = (u_int32_t)sb.st_dev;
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for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
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*fidp++ = *p++;
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#else
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/*
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* Use the file name.
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*
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* XXX
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* Cast the first argument, the BREW ARM compiler is unhappy if
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* we don't.
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*/
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(void)strncpy((char *)fidp, fname, DB_FILE_ID_LEN);
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#endif /* HAVE_STAT */
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if (unique_okay) {
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/* Add in 32-bits of (hopefully) unique number. */
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__os_unique_id(env, &tmp);
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for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
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*fidp++ = *p++;
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/*
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* Initialize/increment the serial number we use to help
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* avoid fileid collisions. Note we don't bother with
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* locking; it's unpleasant to do from down in here, and
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* if we race on this no real harm will be done, since the
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* finished fileid has so many other components.
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*
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* We use the bottom 32-bits of the process ID, hoping they
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* are more random than the top 32-bits (should we be on a
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* machine with 64-bit process IDs).
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*
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* We increment by 100000 on each call as a simple way of
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* randomizing; simply incrementing seems potentially less
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* useful if pids are also simply incremented, since this
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* is process-local and we may be one of a set of processes
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* starting up. 100000 pushes us out of pid space on most
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* 32-bit platforms, and has few interesting properties in
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* base 2.
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*/
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if (DB_GLOBAL(fid_serial) == 0) {
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__os_id(env->dbenv, &pid, NULL);
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DB_GLOBAL(fid_serial) = (u_int32_t)pid;
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} else
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DB_GLOBAL(fid_serial) += 100000;
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for (p = (u_int8_t *)
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&DB_GLOBAL(fid_serial), i = sizeof(u_int32_t); i > 0; --i)
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*fidp++ = *p++;
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}
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return (0);
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}
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