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 2008/01/11 20:50:02 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 */
17int
18__os_fileid(env, fname, unique_okay, fidp)
19	ENV *env;
20	const char *fname;
21	int unique_okay;
22	u_int8_t *fidp;
23{
24	pid_t pid;
25	size_t i;
26	u_int32_t tmp;
27	u_int8_t *p;
28	int ret;
29
30	/*
31	 * The documentation for GetFileInformationByHandle() states that the
32	 * inode-type numbers are not constant between processes.  Actually,
33	 * they are, they're the NTFS MFT indexes.  So, this works on NTFS,
34	 * but perhaps not on other platforms, and perhaps not over a network.
35	 * Can't think of a better solution right now.
36	 */
37	DB_FH *fhp;
38	BY_HANDLE_FILE_INFORMATION fi;
39	BOOL retval = FALSE;
40
41	DB_ASSERT(env, fname != NULL);
42
43	/* Clear the buffer. */
44	memset(fidp, 0, DB_FILE_ID_LEN);
45
46	/*
47	 * First we open the file, because we're not given a handle to it.
48	 * If we can't open it, we're in trouble.
49	 */
50	if ((ret = __os_open(env, fname, 0,
51	    DB_OSO_RDONLY, DB_MODE_400, &fhp)) != 0)
52		return (ret);
53
54	/* File open, get its info */
55	if ((retval = GetFileInformationByHandle(fhp->handle, &fi)) == FALSE)
56		ret = __os_get_syserr();
57	(void)__os_closehandle(env, fhp);
58
59	if (retval == FALSE)
60		return (__os_posix_err(ret));
61
62	/*
63	 * We want the three 32-bit words which tell us the volume ID and
64	 * the file ID.  We make a crude attempt to copy the bytes over to
65	 * the callers buffer.
66	 *
67	 * We don't worry about byte sexing or the actual variable sizes.
68	 *
69	 * When this routine is called from the DB access methods, it's only
70	 * called once -- whatever ID is generated when a database is created
71	 * is stored in the database file's metadata, and that is what is
72	 * saved in the mpool region's information to uniquely identify the
73	 * file.
74	 *
75	 * When called from the mpool layer this routine will be called each
76	 * time a new thread of control wants to share the file, which makes
77	 * things tougher.  As far as byte sexing goes, since the mpool region
78	 * lives on a single host, there's no issue of that -- the entire
79	 * region is byte sex dependent.  As far as variable sizes go, we make
80	 * the simplifying assumption that 32-bit and 64-bit processes will
81	 * get the same 32-bit values if we truncate any returned 64-bit value
82	 * to a 32-bit value.
83	 */
84	tmp = (u_int32_t)fi.nFileIndexLow;
85	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
86		*fidp++ = *p++;
87	tmp = (u_int32_t)fi.nFileIndexHigh;
88	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
89		*fidp++ = *p++;
90
91	if (unique_okay) {
92		/* Add in 32-bits of (hopefully) unique number. */
93		__os_unique_id(env, &tmp);
94		for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
95			*fidp++ = *p++;
96
97		/*
98		 * Initialize/increment the serial number we use to help
99		 * avoid fileid collisions.  Note we don't bother with
100		 * locking; it's unpleasant to do from down in here, and
101		 * if we race on this no real harm will be done, since the
102		 * finished fileid has so many other components.
103		 *
104		 * We use the bottom 32-bits of the process ID, hoping they
105		 * are more random than the top 32-bits (should we be on a
106		 * machine with 64-bit process IDs).
107		 *
108		 * We increment by 100000 on each call as a simple way of
109		 * randomizing; simply incrementing seems potentially less
110		 * useful if pids are also simply incremented, since this
111		 * is process-local and we may be one of a set of processes
112		 * starting up.  100000 pushes us out of pid space on most
113		 * 32-bit platforms, and has few interesting properties in
114		 * base 2.
115		 */
116		if (DB_GLOBAL(fid_serial) == 0) {
117			__os_id(env->dbenv, &pid, NULL);
118			DB_GLOBAL(fid_serial) = (u_int32_t)pid;
119		} else
120			DB_GLOBAL(fid_serial) += 100000;
121
122	} else {
123		tmp = (u_int32_t)fi.dwVolumeSerialNumber;
124		for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
125			*fidp++ = *p++;
126	}
127
128	return (0);
129}
130