msdosfs_fileno.c revision 151897 
1/*-
2 * Copyright (c) 2003-2004 Tim J. Robbins.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26/*
27 * Compress 64-bit file numbers into temporary, unique 32-bit file numbers.
28 * This is needed because the algorithm we use to calculate these numbers
29 * generates 64-bit quantities, but struct dirent's d_fileno member and
30 * struct vnodeattr's va_fileid member only have space for 32 bits.
31 *
32 * 32-bit file numbers are generated sequentially, and stored in a
33 * red-black tree, indexed on 64-bit file number. The mappings do not
34 * persist across reboots (or unmounts); anything that relies on this
35 * (e.g. NFS) will not work correctly. This scheme consumes 32 bytes
36 * of kernel memory per file (on i386), and it may be possible for a user
37 * to cause a panic by creating millions of tiny files.
38 *
39 * As an optimization, we split the file number space between statically
40 * allocated and dynamically allocated. File numbers less than
41 * FILENO_FIRST_DYN are left unchanged and do not have any tree nodes
42 * allocated to them.
43 */
44
45#include <sys/cdefs.h>
46__FBSDID("$FreeBSD: head/sys/fs/msdosfs/msdosfs_fileno.c 151897 2005-10-31 15:41:29Z rwatson $");
47
48#include <sys/param.h>
49#include <sys/systm.h>
50#include <sys/conf.h>
51#include <sys/kernel.h>
52#include <sys/mount.h>
53#include <sys/malloc.h>
54#include <sys/lock.h>
55#include <sys/mutex.h>
56
57#include <fs/msdosfs/bpb.h>
58#include <fs/msdosfs/bootsect.h>
59#include <fs/msdosfs/msdosfsmount.h>
60#include <fs/msdosfs/direntry.h>
61
62static MALLOC_DEFINE(M_MSDOSFSFILENO, "msdosfs_fileno", "MSDOSFS fileno mapping node");
63
64static struct mtx fileno_mtx;
65MTX_SYSINIT(fileno, &fileno_mtx, "MSDOSFS fileno", MTX_DEF);
66
67RB_PROTOTYPE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
68    msdosfs_fileno_compare)
69
70static int msdosfs_fileno_compare(struct msdosfs_fileno *,
71    struct msdosfs_fileno *);
72
73#define	FILENO_FIRST_DYN	0xf0000000
74
75/* Initialize file number mapping structures. */
76void
77msdosfs_fileno_init(mp)
78	struct mount *mp;
79{
80	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
81
82	RB_INIT(&pmp->pm_filenos);
83	pmp->pm_nfileno = FILENO_FIRST_DYN;
84        if (pmp->pm_HugeSectors > 0xffffffff /
85	    (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1)
86		pmp->pm_flags |= MSDOSFS_LARGEFS;
87}
88
89/* Free 32-bit file number generation structures. */
90void
91msdosfs_fileno_free(mp)
92	struct mount *mp;
93{
94	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
95	struct msdosfs_fileno *mf, *next;
96
97	for (mf = RB_MIN(msdosfs_filenotree, &pmp->pm_filenos); mf != NULL;
98	    mf = next) {
99		next = RB_NEXT(msdosfs_filenotree, &pmp->pm_filenos, mf);
100		RB_REMOVE(msdosfs_filenotree, &pmp->pm_filenos, mf);
101		free(mf, M_MSDOSFSFILENO);
102	}
103}
104
105/* Map a 64-bit file number into a 32-bit one. */
106uint32_t
107msdosfs_fileno_map(mp, fileno)
108	struct mount *mp;
109	uint64_t fileno;
110{
111	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
112	struct msdosfs_fileno key, *mf, *tmf;
113	uint32_t mapped;
114
115	if ((pmp->pm_flags & MSDOSFS_LARGEFS) == 0) {
116		KASSERT((uint32_t)fileno == fileno,
117		    ("fileno >32 bits but not a large fs?"));
118		return ((uint32_t)fileno);
119	}
120	if (fileno < FILENO_FIRST_DYN)
121		return ((uint32_t)fileno);
122	mtx_lock(&fileno_mtx);
123	key.mf_fileno64 = fileno;
124	mf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
125	if (mf != NULL) {
126		mapped = mf->mf_fileno32;
127		mtx_unlock(&fileno_mtx);
128		return (mapped);
129	}
130	if (pmp->pm_nfileno < FILENO_FIRST_DYN)
131		panic("msdosfs_fileno_map: wraparound");
132	mtx_unlock(&fileno_mtx);
133	mf = malloc(sizeof(*mf), M_MSDOSFSFILENO, M_WAITOK);
134	mtx_lock(&fileno_mtx);
135	tmf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
136	if (tmf != NULL) {
137		mapped = tmf->mf_fileno32;
138		mtx_unlock(&fileno_mtx);
139		free(mf, M_MSDOSFSFILENO);
140		return (mapped);
141	}
142	mf->mf_fileno64 = fileno;
143	mapped = mf->mf_fileno32 = pmp->pm_nfileno++;
144	RB_INSERT(msdosfs_filenotree, &pmp->pm_filenos, mf);
145	mtx_unlock(&fileno_mtx);
146	return (mapped);
147}
148
149/* Compare by 64-bit file number. */
150static int
151msdosfs_fileno_compare(fa, fb)
152	struct msdosfs_fileno *fa, *fb;
153{
154
155	if (fa->mf_fileno64 > fb->mf_fileno64)
156		return (1);
157	else if (fa->mf_fileno64 < fb->mf_fileno64)
158		return (-1);
159	return (0);
160}
161
162RB_GENERATE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
163    msdosfs_fileno_compare)
164