msdosfs_fileno.c revision 171753 
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 171750 2007-08-07 02:08:06Z bde $");
47
48#include <sys/param.h>
49#include <sys/systm.h>
50#include <sys/kernel.h>
51#include <sys/lock.h>
52#include <sys/malloc.h>
53#include <sys/mount.h>
54#include <sys/mutex.h>
55
56#include <fs/msdosfs/bpb.h>
57#include <fs/msdosfs/direntry.h>
58#include <fs/msdosfs/msdosfsmount.h>
59
60static MALLOC_DEFINE(M_MSDOSFSFILENO, "msdosfs_fileno", "MSDOSFS fileno mapping node");
61
62static struct mtx fileno_mtx;
63MTX_SYSINIT(fileno, &fileno_mtx, "MSDOSFS fileno", MTX_DEF);
64
65RB_PROTOTYPE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
66    msdosfs_fileno_compare)
67
68static int msdosfs_fileno_compare(struct msdosfs_fileno *,
69    struct msdosfs_fileno *);
70
71#define	FILENO_FIRST_DYN	0xf0000000
72
73/* Initialize file number mapping structures. */
74void
75msdosfs_fileno_init(mp)
76	struct mount *mp;
77{
78	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
79
80	RB_INIT(&pmp->pm_filenos);
81	pmp->pm_nfileno = FILENO_FIRST_DYN;
82        if (pmp->pm_HugeSectors > 0xffffffff /
83	    (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1)
84		pmp->pm_flags |= MSDOSFS_LARGEFS;
85}
86
87/* Free 32-bit file number generation structures. */
88void
89msdosfs_fileno_free(mp)
90	struct mount *mp;
91{
92	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
93	struct msdosfs_fileno *mf, *next;
94
95	for (mf = RB_MIN(msdosfs_filenotree, &pmp->pm_filenos); mf != NULL;
96	    mf = next) {
97		next = RB_NEXT(msdosfs_filenotree, &pmp->pm_filenos, mf);
98		RB_REMOVE(msdosfs_filenotree, &pmp->pm_filenos, mf);
99		free(mf, M_MSDOSFSFILENO);
100	}
101}
102
103/* Map a 64-bit file number into a 32-bit one. */
104uint32_t
105msdosfs_fileno_map(mp, fileno)
106	struct mount *mp;
107	uint64_t fileno;
108{
109	struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
110	struct msdosfs_fileno key, *mf, *tmf;
111	uint32_t mapped;
112
113	if ((pmp->pm_flags & MSDOSFS_LARGEFS) == 0) {
114		KASSERT((uint32_t)fileno == fileno,
115		    ("fileno >32 bits but not a large fs?"));
116		return ((uint32_t)fileno);
117	}
118	if (fileno < FILENO_FIRST_DYN)
119		return ((uint32_t)fileno);
120	mtx_lock(&fileno_mtx);
121	key.mf_fileno64 = fileno;
122	mf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
123	if (mf != NULL) {
124		mapped = mf->mf_fileno32;
125		mtx_unlock(&fileno_mtx);
126		return (mapped);
127	}
128	if (pmp->pm_nfileno < FILENO_FIRST_DYN)
129		panic("msdosfs_fileno_map: wraparound");
130	mtx_unlock(&fileno_mtx);
131	mf = malloc(sizeof(*mf), M_MSDOSFSFILENO, M_WAITOK);
132	mtx_lock(&fileno_mtx);
133	tmf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
134	if (tmf != NULL) {
135		mapped = tmf->mf_fileno32;
136		mtx_unlock(&fileno_mtx);
137		free(mf, M_MSDOSFSFILENO);
138		return (mapped);
139	}
140	mf->mf_fileno64 = fileno;
141	mapped = mf->mf_fileno32 = pmp->pm_nfileno++;
142	RB_INSERT(msdosfs_filenotree, &pmp->pm_filenos, mf);
143	mtx_unlock(&fileno_mtx);
144	return (mapped);
145}
146
147/* Compare by 64-bit file number. */
148static int
149msdosfs_fileno_compare(fa, fb)
150	struct msdosfs_fileno *fa, *fb;
151{
152
153	if (fa->mf_fileno64 > fb->mf_fileno64)
154		return (1);
155	else if (fa->mf_fileno64 < fb->mf_fileno64)
156		return (-1);
157	return (0);
158}
159
160RB_GENERATE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
161    msdosfs_fileno_compare)
162