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libmount: avoid duplicate loopdevs
[thirdparty/util-linux.git] / libmount / src / context_loopdev.c
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1/*
2 * Copyright (C) 2011 Karel Zak <kzak@redhat.com>
3 *
4 * This file may be redistributed under the terms of the
5 * GNU Lesser General Public License.
6 */
7
8/*
9 * DOCS: - "lo@" prefix for fstype is unsupported
10 * - encyption= mount option for loop device is unssuported
11 */
12
13#include <blkid.h>
14
15#include "mountP.h"
16#include "loopdev.h"
17#include "linux_version.h"
18
19
20int mnt_context_is_loopdev(struct libmnt_context *cxt)
21{
22 const char *type, *src;
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23
24 assert(cxt);
c8512236 25
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26 /* The mount flags have to be merged, otherwise we have to use
27 * expensive mnt_context_get_user_mflags() instead of cxt->user_mountflags. */
28 assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
29
30 if (!cxt->fs)
31 return 0;
32 src = mnt_fs_get_srcpath(cxt->fs);
33 if (!src)
34 return 0; /* backing file not set */
35
36 if (cxt->user_mountflags & (MNT_MS_LOOP |
37 MNT_MS_OFFSET |
1a7a421e 38 MNT_MS_SIZELIMIT |
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39 MNT_MS_ENCRYPTION)) {
40
41 DBG(CXT, mnt_debug_h(cxt, "loopdev specific options detected"));
7f8b2bf3 42 return 1;
c8512236 43 }
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44
45 if (cxt->mountflags & (MS_BIND | MS_MOVE | MS_PROPAGATION))
46 return 0;
47
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48 /* Automatically create a loop device from a regular file if a
49 * filesystem is not specified or the filesystem is known for libblkid
50 * (these filesystems work with block devices only). The file size
51 * should be at least 1KiB otherwise we will create empty loopdev where
52 * is no mountable filesystem...
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53 *
54 * Note that there is not a restriction (on kernel side) that prevents regular
55 * file as a mount(2) source argument. A filesystem that is able to mount
56 * regular files could be implemented.
57 */
58 type = mnt_fs_get_fstype(cxt->fs);
7f8b2bf3 59
c70d9d76 60 if (mnt_fs_is_regular(cxt->fs) &&
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61 (!type || strcmp(type, "auto") == 0 || blkid_known_fstype(type))) {
62 struct stat st;
63
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64 if (stat(src, &st) == 0 && S_ISREG(st.st_mode) &&
65 st.st_size > 1024)
66 return 1;
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67 }
68
c8512236 69 return 0;
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70}
71
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72
73/* Check, if there already exists a mounted loop device on the mountpoint node
74 * with the same parameters.
75 */
76static int is_mounted_same_loopfile(struct libmnt_context *cxt,
77 const char *target,
78 const char *backing_file,
79 uint64_t offset)
80{
81 struct libmnt_table *tb;
82 struct libmnt_iter itr;
83 struct libmnt_fs *fs;
84 struct libmnt_cache *cache;
85
86 assert(cxt);
87 assert(cxt->fs);
88 assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
89
90 if (!target || !backing_file || mnt_context_get_mtab(cxt, &tb))
91 return 0;
92
93 DBG(CXT, mnt_debug_h(cxt, "checking if %s mounted on %d",
94 backing_file, target));
95
96 cache = mnt_context_get_cache(cxt);
97 mnt_reset_iter(&itr, MNT_ITER_BACKWARD);
98
99 /* Search for mountpoint node in mtab, procceed if any of these has the
100 * loop option set or the device is a loop device
101 */
102 while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
103 const char *src = mnt_fs_get_source(fs);
104 const char *opts = mnt_fs_get_user_options(fs);
105 char *val;
106 size_t len;
107 int res = 0;
108
109 if (!src || !mnt_fs_match_target(fs, target, cache))
110 continue;
111
112 if (strncmp(src, "/dev/loop", 9) == 0) {
113 res = loopdev_is_used((char *) src, backing_file,
114 offset, LOOPDEV_FL_OFFSET);
115
116 } else if (opts && (cxt->user_mountflags & MNT_MS_LOOP) &&
117 mnt_optstr_get_option(opts, "loop", &val, &len) == 0 && val) {
118
119 val = strndup(val, len);
120 res = loopdev_is_used((char *) val, backing_file,
121 offset, LOOPDEV_FL_OFFSET);
122 free(val);
123 }
124
125 if (res) {
126 DBG(CXT, mnt_debug_h(cxt, "%s already mounted", backing_file));
127 return 1;
128 }
129 }
130
131 return 0;
132}
133
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134int mnt_context_setup_loopdev(struct libmnt_context *cxt)
135{
f0d3ff0a 136 const char *backing_file, *optstr, *loopdev = NULL;
1a7a421e 137 char *val = NULL, *enc = NULL, *pwd = NULL;
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138 size_t len;
139 struct loopdev_cxt lc;
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140 int rc = 0, lo_flags = 0;
141 uint64_t offset = 0, sizelimit = 0;
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142
143 assert(cxt);
144 assert(cxt->fs);
145 assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
146
147 backing_file = mnt_fs_get_srcpath(cxt->fs);
148 if (!backing_file)
149 return -EINVAL;
150
151 DBG(CXT, mnt_debug_h(cxt, "trying to setup loopdev for %s", backing_file));
152
153 if (cxt->mountflags & MS_RDONLY) {
154 DBG(CXT, mnt_debug_h(cxt, "enabling READ-ONLY flag"));
155 lo_flags |= LO_FLAGS_READ_ONLY;
156 }
365e5a7c 157
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158 loopcxt_init(&lc, 0);
159
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160 ON_DBG(CXT, loopcxt_enable_debug(&lc, 1));
161
b9fd3340 162 optstr = mnt_fs_get_user_options(cxt->fs);
7f8b2bf3 163
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164 /*
165 * loop=
166 */
167 if (rc == 0 && (cxt->user_mountflags & MNT_MS_LOOP) &&
168 mnt_optstr_get_option(optstr, "loop", &val, &len) == 0 && val) {
169
170 val = strndup(val, len);
171 rc = val ? loopcxt_set_device(&lc, val) : -ENOMEM;
172 free(val);
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173
174 if (rc == 0)
175 loopdev = loopcxt_get_device(&lc);
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176 }
177
178 /*
179 * offset=
180 */
181 if (rc == 0 && (cxt->user_mountflags & MNT_MS_OFFSET) &&
182 mnt_optstr_get_option(optstr, "offset", &val, &len) == 0) {
183 rc = mnt_parse_offset(val, len, &offset);
184 if (rc)
185 DBG(CXT, mnt_debug_h(cxt, "failed to parse offset="));
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186 }
187
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188 /*
189 * sizelimit=
190 */
191 if (rc == 0 && (cxt->user_mountflags & MNT_MS_SIZELIMIT) &&
192 mnt_optstr_get_option(optstr, "sizelimit", &val, &len) == 0) {
193 rc = mnt_parse_offset(val, len, &sizelimit);
194 if (rc)
195 DBG(CXT, mnt_debug_h(cxt, "failed to parse sizelimit="));
196 }
197
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198 /*
199 * encryption=
200 */
201 if (rc == 0 && (cxt->user_mountflags & MNT_MS_ENCRYPTION) &&
202 mnt_optstr_get_option(optstr, "encryption", &val, &len) == 0) {
203 enc = strndup(val, len);
204 if (val && !enc)
205 rc = -ENOMEM;
206 if (enc && cxt->pwd_get_cb) {
207 DBG(CXT, mnt_debug_h(cxt, "asking for pass"));
208 pwd = cxt->pwd_get_cb(cxt);
209 }
210 }
211
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212 if (rc == 0 && is_mounted_same_loopfile(cxt,
213 mnt_context_get_target(cxt),
214 backing_file, offset))
215 rc = -EBUSY;
216
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217 if (rc)
218 goto done;
219
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220 /* since 2.6.37 we don't have to store backing filename to mtab
221 * because kernel provides the name in /sys.
222 */
223 if (get_linux_version() >= KERNEL_VERSION(2, 6, 37) ||
224 !cxt->mtab_writable) {
225 DBG(CXT, mnt_debug_h(cxt, "enabling AUTOCLEAR flag"));
226 lo_flags |= LO_FLAGS_AUTOCLEAR;
227 }
228
229 do {
230 /* found free device */
231 if (!loopdev) {
232 rc = loopcxt_find_unused(&lc);
233 if (rc)
234 goto done;
235 DBG(CXT, mnt_debug_h(cxt, "trying to use %s",
236 loopcxt_get_device(&lc)));
237 }
238
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239 /* set device attributes
240 * -- note that loopcxt_find_unused() resets "lc"
241 */
7f8b2bf3 242 rc = loopcxt_set_backing_file(&lc, backing_file);
7f8b2bf3 243
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244 if (!rc && offset)
245 rc = loopcxt_set_offset(&lc, offset);
246 if (!rc && sizelimit)
247 rc = loopcxt_set_sizelimit(&lc, sizelimit);
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248 if (!rc && enc && pwd)
249 loopcxt_set_encryption(&lc, enc, pwd);
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250 if (!rc)
251 loopcxt_set_flags(&lc, lo_flags);
252 if (rc) {
253 DBG(CXT, mnt_debug_h(cxt, "failed to set loopdev attributes"));
254 goto done;
255 }
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256
257 /* setup the device */
258 rc = loopcxt_setup_device(&lc);
259 if (!rc)
260 break; /* success */
261
262 if (loopdev || rc != -EBUSY) {
263 DBG(CXT, mnt_debug_h(cxt, "failed to setup device"));
b9fd3340 264 goto done;
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265 }
266 DBG(CXT, mnt_debug_h(cxt, "loopdev stolen...trying again"));
267 } while (1);
268
269 if (!rc)
270 rc = mnt_fs_set_source(cxt->fs, loopcxt_get_device(&lc));
271
272 if (!rc) {
273 /* success */
274 cxt->flags |= MNT_FL_LOOPDEV_READY;
275
276 if ((cxt->user_mountflags & MNT_MS_LOOP) &&
f0d3ff0a 277 loopcxt_is_autoclear(&lc)) {
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278 /*
279 * autoclear flag accepted by kernel, don't store
280 * the "loop=" option to mtab.
281 */
282 cxt->user_mountflags &= ~MNT_MS_LOOP;
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283 mnt_optstr_remove_option(&cxt->fs->user_optstr, "loop");
284 }
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285
286 if (!(cxt->mountflags & MS_RDONLY) &&
287 loopcxt_is_readonly(&lc))
288 /*
289 * mount planned read-write, but loopdev is read-only,
290 * let's fix mount options...
291 */
292 cxt->mountflags |= MS_RDONLY;
293
294
295 /* we have to keep the device open until mount(1),
296 * otherwise it will auto-cleared by kernel
297 */
298 cxt->loopdev_fd = loopcxt_get_fd(&lc);
299 loopcxt_set_fd(&lc, -1, 0);
300 }
301done:
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302 free(enc);
303 if (pwd && cxt->pwd_release_cb) {
304 DBG(CXT, mnt_debug_h(cxt, "release pass"));
305 cxt->pwd_release_cb(cxt, pwd);
306 }
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307 loopcxt_deinit(&lc);
308 return rc;
309}
310
311/*
312 * Deletes loop device
313 */
314int mnt_context_delete_loopdev(struct libmnt_context *cxt)
315{
316 const char *src;
317 int rc;
318
319 assert(cxt);
320 assert(cxt->fs);
321
322 src = mnt_fs_get_srcpath(cxt->fs);
323 if (!src)
324 return -EINVAL;
325
326 if (cxt->loopdev_fd > -1)
327 close(cxt->loopdev_fd);
328
329 rc = loopdev_delete(src);
330 cxt->flags &= ~MNT_FL_LOOPDEV_READY;
331 cxt->loopdev_fd = -1;
332
333 DBG(CXT, mnt_debug_h(cxt, "loopdev deleted [rc=%d]", rc));
334 return rc;
335}
336
337/*
338 * Clears loopdev stuff in context, should be called after
339 * failed or successful mount(2).
340 */
341int mnt_context_clear_loopdev(struct libmnt_context *cxt)
342{
343 assert(cxt);
344
345 if (mnt_context_get_status(cxt) == 0 &&
346 (cxt->flags & MNT_FL_LOOPDEV_READY)) {
347 /*
348 * mount(2) failed, delete loopdev
349 */
350 mnt_context_delete_loopdev(cxt);
351
352 } else if (cxt->loopdev_fd > -1) {
353 /*
354 * mount(2) success, close the device
355 */
356 DBG(CXT, mnt_debug_h(cxt, "closing loopdev FD"));
357 close(cxt->loopdev_fd);
358 }
359 cxt->loopdev_fd = -1;
360 return 0;
361}
362