Import BSDDB 4.7.25 (as of svn r89086)

os/os_fid.c

@@ -0,0 +1,134 @@
+/*-
+ * See the file LICENSE for redistribution information.
+ *
+ * Copyright (c) 1996,2008 Oracle.  All rights reserved.
+ *
+ * $Id: os_fid.c 63573 2008-05-23 21:43:21Z trent.nelson $
+ */
+
+#include "db_config.h"
+
+#include "db_int.h"
+
+/*
+ * __os_fileid --
+ *	Return a unique identifier for a file.
+ *
+ * PUBLIC: int __os_fileid __P((ENV *, const char *, int, u_int8_t *));
+ */
+int
+__os_fileid(env, fname, unique_okay, fidp)
+	ENV *env;
+	const char *fname;
+	int unique_okay;
+	u_int8_t *fidp;
+{
+	pid_t pid;
+	size_t i;
+	u_int32_t tmp;
+	u_int8_t *p;
+
+#ifdef HAVE_STAT
+	struct stat sb;
+	int ret;
+
+	/*
+	 * The structure of a fileid on a POSIX/UNIX system is:
+	 *
+	 *	ino[4] dev[4] unique-ID[4] serial-counter[4] empty[4].
+	 *
+	 * For real files, which have a backing inode and device, the first
+	 * 8 bytes are filled in and the following bytes are left 0.  For
+	 * temporary files, the following 12 bytes are filled in.
+	 *
+	 * Clear the buffer.
+	 */
+	memset(fidp, 0, DB_FILE_ID_LEN);
+	RETRY_CHK((stat(CHAR_STAR_CAST fname, &sb)), ret);
+	if (ret != 0) {
+		__db_syserr(env, ret, "stat: %s", fname);
+		return (__os_posix_err(ret));
+	}
+
+	/*
+	 * !!!
+	 * Nothing is ever big enough -- on Sparc V9, st_ino, st_dev and the
+	 * time_t types are all 8 bytes.  As DB_FILE_ID_LEN is only 20 bytes,
+	 * we convert to a (potentially) smaller fixed-size type and use it.
+	 *
+	 * 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.  When we're called from the mpool layer, though,
+	 * we need to be careful not to include anything that isn't
+	 * reproducible for a given file, such as the timestamp or serial
+	 * number.
+	 */
+	tmp = (u_int32_t)sb.st_ino;
+	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
+		*fidp++ = *p++;
+
+	tmp = (u_int32_t)sb.st_dev;
+	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
+		*fidp++ = *p++;
+#else
+	 /*
+	  * Use the file name.
+	  *
+	  * XXX
+	  * Cast the first argument, the BREW ARM compiler is unhappy if
+	  * we don't.
+	  */
+	 (void)strncpy((char *)fidp, fname, DB_FILE_ID_LEN);
+#endif /* HAVE_STAT */
+
+	if (unique_okay) {
+		/* Add in 32-bits of (hopefully) unique number. */
+		__os_unique_id(env, &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(env->dbenv, &pid, NULL);
+			DB_GLOBAL(fid_serial) = (u_int32_t)pid;
+		} else
+			DB_GLOBAL(fid_serial) += 100000;
+
+		for (p = (u_int8_t *)
+		    &DB_GLOBAL(fid_serial), i = sizeof(u_int32_t); i > 0; --i)
+			*fidp++ = *p++;
+	}
+
+	return (0);
+}