1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 =================================== !! 3 ===============================================
4 Cache on Already Mounted Filesystem !! 4 CacheFiles: CACHE ON ALREADY MOUNTED FILESYSTEM
5 =================================== !! 5 ===============================================
6 6
7 .. Contents: 7 .. Contents:
8 8
9 (*) Overview. 9 (*) Overview.
10 10
11 (*) Requirements. 11 (*) Requirements.
12 12
13 (*) Configuration. 13 (*) Configuration.
14 14
15 (*) Starting the cache. 15 (*) Starting the cache.
16 16
17 (*) Things to avoid. 17 (*) Things to avoid.
18 18
19 (*) Cache culling. 19 (*) Cache culling.
20 20
21 (*) Cache structure. 21 (*) Cache structure.
22 22
23 (*) Security model and SELinux. 23 (*) Security model and SELinux.
24 24
25 (*) A note on security. 25 (*) A note on security.
26 26
27 (*) Statistical information. 27 (*) Statistical information.
28 28
29 (*) Debugging. 29 (*) Debugging.
30 30
31 (*) On-demand Read. <<
32 31
33 32
34 Overview 33 Overview
35 ======== 34 ========
36 35
37 CacheFiles is a caching backend that's meant t 36 CacheFiles is a caching backend that's meant to use as a cache a directory on
38 an already mounted filesystem of a local type 37 an already mounted filesystem of a local type (such as Ext3).
39 38
40 CacheFiles uses a userspace daemon to do some 39 CacheFiles uses a userspace daemon to do some of the cache management - such as
41 reaping stale nodes and culling. This is call 40 reaping stale nodes and culling. This is called cachefilesd and lives in
42 /sbin. 41 /sbin.
43 42
44 The filesystem and data integrity of the cache 43 The filesystem and data integrity of the cache are only as good as those of the
45 filesystem providing the backing services. No 44 filesystem providing the backing services. Note that CacheFiles does not
46 attempt to journal anything since the journall 45 attempt to journal anything since the journalling interfaces of the various
47 filesystems are very specific in nature. 46 filesystems are very specific in nature.
48 47
49 CacheFiles creates a misc character device - " 48 CacheFiles creates a misc character device - "/dev/cachefiles" - that is used
50 to communication with the daemon. Only one th 49 to communication with the daemon. Only one thing may have this open at once,
51 and while it is open, a cache is at least part 50 and while it is open, a cache is at least partially in existence. The daemon
52 opens this and sends commands down it to contr 51 opens this and sends commands down it to control the cache.
53 52
54 CacheFiles is currently limited to a single ca 53 CacheFiles is currently limited to a single cache.
55 54
56 CacheFiles attempts to maintain at least a cer 55 CacheFiles attempts to maintain at least a certain percentage of free space on
57 the filesystem, shrinking the cache by culling 56 the filesystem, shrinking the cache by culling the objects it contains to make
58 space if necessary - see the "Cache Culling" s 57 space if necessary - see the "Cache Culling" section. This means it can be
59 placed on the same medium as a live set of dat 58 placed on the same medium as a live set of data, and will expand to make use of
60 spare space and automatically contract when th 59 spare space and automatically contract when the set of data requires more
61 space. 60 space.
62 61
63 62
64 63
65 Requirements 64 Requirements
66 ============ 65 ============
67 66
68 The use of CacheFiles and its daemon requires 67 The use of CacheFiles and its daemon requires the following features to be
69 available in the system and in the cache files 68 available in the system and in the cache filesystem:
70 69
71 - dnotify. 70 - dnotify.
72 71
73 - extended attributes (xattrs). 72 - extended attributes (xattrs).
74 73
75 - openat() and friends. 74 - openat() and friends.
76 75
77 - bmap() support on files in the files 76 - bmap() support on files in the filesystem (FIBMAP ioctl).
78 77
79 - The use of bmap() to detect a partia 78 - The use of bmap() to detect a partial page at the end of the file.
80 79
81 It is strongly recommended that the "dir_index 80 It is strongly recommended that the "dir_index" option is enabled on Ext3
82 filesystems being used as a cache. 81 filesystems being used as a cache.
83 82
84 83
85 Configuration 84 Configuration
86 ============= 85 =============
87 86
88 The cache is configured by a script in /etc/ca 87 The cache is configured by a script in /etc/cachefilesd.conf. These commands
89 set up cache ready for use. The following scr 88 set up cache ready for use. The following script commands are available:
90 89
91 brun <N>%, bcull <N>%, bstop <N>%, frun <N>%, 90 brun <N>%, bcull <N>%, bstop <N>%, frun <N>%, fcull <N>%, fstop <N>%
92 Configure the culling limits. Optiona 91 Configure the culling limits. Optional. See the section on culling
93 The defaults are 7% (run), 5% (cull) a 92 The defaults are 7% (run), 5% (cull) and 1% (stop) respectively.
94 93
95 The commands beginning with a 'b' are 94 The commands beginning with a 'b' are file space (block) limits, those
96 beginning with an 'f' are file count l 95 beginning with an 'f' are file count limits.
97 96
98 dir <path> 97 dir <path>
99 Specify the directory containing the r 98 Specify the directory containing the root of the cache. Mandatory.
100 99
101 tag <name> 100 tag <name>
102 Specify a tag to FS-Cache to use in di 101 Specify a tag to FS-Cache to use in distinguishing multiple caches.
103 Optional. The default is "CacheFiles" 102 Optional. The default is "CacheFiles".
104 103
105 debug <mask> 104 debug <mask>
106 Specify a numeric bitmask to control d 105 Specify a numeric bitmask to control debugging in the kernel module.
107 Optional. The default is zero (all of 106 Optional. The default is zero (all off). The following values can be
108 OR'd into the mask to collect various 107 OR'd into the mask to collect various information:
109 108
110 == ====================== 109 == =================================================
111 1 Turn on trace of funct 110 1 Turn on trace of function entry (_enter() macros)
112 2 Turn on trace of funct 111 2 Turn on trace of function exit (_leave() macros)
113 4 Turn on trace of inter 112 4 Turn on trace of internal debug points (_debug())
114 == ====================== 113 == =================================================
115 114
116 This mask can also be set through sysf 115 This mask can also be set through sysfs, eg::
117 116
118 echo 5 > /sys/module/cachefile !! 117 echo 5 >/sys/modules/cachefiles/parameters/debug
119 118
120 119
121 Starting the Cache 120 Starting the Cache
122 ================== 121 ==================
123 122
124 The cache is started by running the daemon. T 123 The cache is started by running the daemon. The daemon opens the cache device,
125 configures the cache and tells it to begin cac 124 configures the cache and tells it to begin caching. At that point the cache
126 binds to fscache and the cache becomes live. 125 binds to fscache and the cache becomes live.
127 126
128 The daemon is run as follows:: 127 The daemon is run as follows::
129 128
130 /sbin/cachefilesd [-d]* [-s] [-n] [-f 129 /sbin/cachefilesd [-d]* [-s] [-n] [-f <configfile>]
131 130
132 The flags are: 131 The flags are:
133 132
134 ``-d`` 133 ``-d``
135 Increase the debugging level. This ca 134 Increase the debugging level. This can be specified multiple times and
136 is cumulative with itself. 135 is cumulative with itself.
137 136
138 ``-s`` 137 ``-s``
139 Send messages to stderr instead of sys 138 Send messages to stderr instead of syslog.
140 139
141 ``-n`` 140 ``-n``
142 Don't daemonise and go into background 141 Don't daemonise and go into background.
143 142
144 ``-f <configfile>`` 143 ``-f <configfile>``
145 Use an alternative configuration file 144 Use an alternative configuration file rather than the default one.
146 145
147 146
148 Things to Avoid 147 Things to Avoid
149 =============== 148 ===============
150 149
151 Do not mount other things within the cache as 150 Do not mount other things within the cache as this will cause problems. The
152 kernel module contains its own very cut-down p 151 kernel module contains its own very cut-down path walking facility that ignores
153 mountpoints, but the daemon can't avoid them. 152 mountpoints, but the daemon can't avoid them.
154 153
155 Do not create, rename or unlink files and dire 154 Do not create, rename or unlink files and directories in the cache while the
156 cache is active, as this may cause the state t 155 cache is active, as this may cause the state to become uncertain.
157 156
158 Renaming files in the cache might make objects 157 Renaming files in the cache might make objects appear to be other objects (the
159 filename is part of the lookup key). 158 filename is part of the lookup key).
160 159
161 Do not change or remove the extended attribute 160 Do not change or remove the extended attributes attached to cache files by the
162 cache as this will cause the cache state manag 161 cache as this will cause the cache state management to get confused.
163 162
164 Do not create files or directories in the cach 163 Do not create files or directories in the cache, lest the cache get confused or
165 serve incorrect data. 164 serve incorrect data.
166 165
167 Do not chmod files in the cache. The module c 166 Do not chmod files in the cache. The module creates things with minimal
168 permissions to prevent random users being able 167 permissions to prevent random users being able to access them directly.
169 168
170 169
171 Cache Culling 170 Cache Culling
172 ============= 171 =============
173 172
174 The cache may need culling occasionally to mak 173 The cache may need culling occasionally to make space. This involves
175 discarding objects from the cache that have be 174 discarding objects from the cache that have been used less recently than
176 anything else. Culling is based on the access 175 anything else. Culling is based on the access time of data objects. Empty
177 directories are culled if not in use. 176 directories are culled if not in use.
178 177
179 Cache culling is done on the basis of the perc 178 Cache culling is done on the basis of the percentage of blocks and the
180 percentage of files available in the underlyin 179 percentage of files available in the underlying filesystem. There are six
181 "limits": 180 "limits":
182 181
183 brun, frun 182 brun, frun
184 If the amount of free space and the numbe 183 If the amount of free space and the number of available files in the cache
185 rises above both these limits, then culli 184 rises above both these limits, then culling is turned off.
186 185
187 bcull, fcull 186 bcull, fcull
188 If the amount of available space or the n 187 If the amount of available space or the number of available files in the
189 cache falls below either of these limits, 188 cache falls below either of these limits, then culling is started.
190 189
191 bstop, fstop 190 bstop, fstop
192 If the amount of available space or the n 191 If the amount of available space or the number of available files in the
193 cache falls below either of these limits, 192 cache falls below either of these limits, then no further allocation of
194 disk space or files is permitted until cu 193 disk space or files is permitted until culling has raised things above
195 these limits again. 194 these limits again.
196 195
197 These must be configured thusly:: 196 These must be configured thusly::
198 197
199 0 <= bstop < bcull < brun < 100 198 0 <= bstop < bcull < brun < 100
200 0 <= fstop < fcull < frun < 100 199 0 <= fstop < fcull < frun < 100
201 200
202 Note that these are percentages of available s 201 Note that these are percentages of available space and available files, and do
203 _not_ appear as 100 minus the percentage displ 202 _not_ appear as 100 minus the percentage displayed by the "df" program.
204 203
205 The userspace daemon scans the cache to build 204 The userspace daemon scans the cache to build up a table of cullable objects.
206 These are then culled in least recently used o 205 These are then culled in least recently used order. A new scan of the cache is
207 started as soon as space is made in the table. 206 started as soon as space is made in the table. Objects will be skipped if
208 their atimes have changed or if the kernel mod 207 their atimes have changed or if the kernel module says it is still using them.
209 208
210 209
211 Cache Structure 210 Cache Structure
212 =============== 211 ===============
213 212
214 The CacheFiles module will create two director 213 The CacheFiles module will create two directories in the directory it was
215 given: 214 given:
216 215
217 * cache/ 216 * cache/
218 * graveyard/ 217 * graveyard/
219 218
220 The active cache objects all reside in the fir 219 The active cache objects all reside in the first directory. The CacheFiles
221 kernel module moves any retired or culled obje 220 kernel module moves any retired or culled objects that it can't simply unlink
222 to the graveyard from which the daemon will ac 221 to the graveyard from which the daemon will actually delete them.
223 222
224 The daemon uses dnotify to monitor the graveya 223 The daemon uses dnotify to monitor the graveyard directory, and will delete
225 anything that appears therein. 224 anything that appears therein.
226 225
227 226
228 The module represents index objects as directo 227 The module represents index objects as directories with the filename "I..." or
229 "J...". Note that the "cache/" directory is i 228 "J...". Note that the "cache/" directory is itself a special index.
230 229
231 Data objects are represented as files if they 230 Data objects are represented as files if they have no children, or directories
232 if they do. Their filenames all begin "D..." 231 if they do. Their filenames all begin "D..." or "E...". If represented as a
233 directory, data objects will have a file in th 232 directory, data objects will have a file in the directory called "data" that
234 actually holds the data. 233 actually holds the data.
235 234
236 Special objects are similar to data objects, e 235 Special objects are similar to data objects, except their filenames begin
237 "S..." or "T...". 236 "S..." or "T...".
238 237
239 238
240 If an object has children, then it will be rep 239 If an object has children, then it will be represented as a directory.
241 Immediately in the representative directory ar 240 Immediately in the representative directory are a collection of directories
242 named for hash values of the child object keys 241 named for hash values of the child object keys with an '@' prepended. Into
243 this directory, if possible, will be placed th 242 this directory, if possible, will be placed the representations of the child
244 objects:: 243 objects::
245 244
246 /INDEX /INDEX /INDEX 245 /INDEX /INDEX /INDEX /DATA FILES
247 /=========/==========/================ 246 /=========/==========/=================================/================
248 cache/@4a/I03nfs/@30/Ji000000000000000 247 cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400
249 cache/@4a/I03nfs/@30/Ji000000000000000 248 cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...DB1ry
250 cache/@4a/I03nfs/@30/Ji000000000000000 249 cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...N22ry
251 cache/@4a/I03nfs/@30/Ji000000000000000 250 cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...FP1ry
252 251
253 252
254 If the key is so long that it exceeds NAME_MAX 253 If the key is so long that it exceeds NAME_MAX with the decorations added on to
255 it, then it will be cut into pieces, the first 254 it, then it will be cut into pieces, the first few of which will be used to
256 make a nest of directories, and the last one o 255 make a nest of directories, and the last one of which will be the objects
257 inside the last directory. The names of the i 256 inside the last directory. The names of the intermediate directories will have
258 '+' prepended:: 257 '+' prepended::
259 258
260 J1223/@23/+xy...z/+kl...m/Epqr 259 J1223/@23/+xy...z/+kl...m/Epqr
261 260
262 261
263 Note that keys are raw data, and not only may 262 Note that keys are raw data, and not only may they exceed NAME_MAX in size,
264 they may also contain things like '/' and NUL 263 they may also contain things like '/' and NUL characters, and so they may not
265 be suitable for turning directly into a filena 264 be suitable for turning directly into a filename.
266 265
267 To handle this, CacheFiles will use a suitably 266 To handle this, CacheFiles will use a suitably printable filename directly and
268 "base-64" encode ones that aren't directly sui 267 "base-64" encode ones that aren't directly suitable. The two versions of
269 object filenames indicate the encoding: 268 object filenames indicate the encoding:
270 269
271 =============== =============== ====== 270 =============== =============== ===============
272 OBJECT TYPE PRINTABLE ENCODE 271 OBJECT TYPE PRINTABLE ENCODED
273 =============== =============== ====== 272 =============== =============== ===============
274 Index "I..." "J..." 273 Index "I..." "J..."
275 Data "D..." "E..." 274 Data "D..." "E..."
276 Special "S..." "T..." 275 Special "S..." "T..."
277 =============== =============== ====== 276 =============== =============== ===============
278 277
279 Intermediate directories are always "@" or "+" 278 Intermediate directories are always "@" or "+" as appropriate.
280 279
281 280
282 Each object in the cache has an extended attri 281 Each object in the cache has an extended attribute label that holds the object
283 type ID (required to distinguish special objec 282 type ID (required to distinguish special objects) and the auxiliary data from
284 the netfs. The latter is used to detect stale 283 the netfs. The latter is used to detect stale objects in the cache and update
285 or retire them. 284 or retire them.
286 285
287 286
288 Note that CacheFiles will erase from the cache 287 Note that CacheFiles will erase from the cache any file it doesn't recognise or
289 any file of an incorrect type (such as a FIFO 288 any file of an incorrect type (such as a FIFO file or a device file).
290 289
291 290
292 Security Model and SELinux 291 Security Model and SELinux
293 ========================== 292 ==========================
294 293
295 CacheFiles is implemented to deal properly wit 294 CacheFiles is implemented to deal properly with the LSM security features of
296 the Linux kernel and the SELinux facility. 295 the Linux kernel and the SELinux facility.
297 296
298 One of the problems that CacheFiles faces is t 297 One of the problems that CacheFiles faces is that it is generally acting on
299 behalf of a process, and running in that proce 298 behalf of a process, and running in that process's context, and that includes a
300 security context that is not appropriate for a 299 security context that is not appropriate for accessing the cache - either
301 because the files in the cache are inaccessibl 300 because the files in the cache are inaccessible to that process, or because if
302 the process creates a file in the cache, that 301 the process creates a file in the cache, that file may be inaccessible to other
303 processes. 302 processes.
304 303
305 The way CacheFiles works is to temporarily cha 304 The way CacheFiles works is to temporarily change the security context (fsuid,
306 fsgid and actor security label) that the proce 305 fsgid and actor security label) that the process acts as - without changing the
307 security context of the process when it the ta 306 security context of the process when it the target of an operation performed by
308 some other process (so signalling and suchlike 307 some other process (so signalling and suchlike still work correctly).
309 308
310 309
311 When the CacheFiles module is asked to bind to 310 When the CacheFiles module is asked to bind to its cache, it:
312 311
313 (1) Finds the security label attached to the 312 (1) Finds the security label attached to the root cache directory and uses
314 that as the security label with which it 313 that as the security label with which it will create files. By default,
315 this is:: 314 this is::
316 315
317 cachefiles_var_t 316 cachefiles_var_t
318 317
319 (2) Finds the security label of the process w 318 (2) Finds the security label of the process which issued the bind request
320 (presumed to be the cachefilesd daemon), 319 (presumed to be the cachefilesd daemon), which by default will be::
321 320
322 cachefilesd_t 321 cachefilesd_t
323 322
324 and asks LSM to supply a security ID as w 323 and asks LSM to supply a security ID as which it should act given the
325 daemon's label. By default, this will be 324 daemon's label. By default, this will be::
326 325
327 cachefiles_kernel_t 326 cachefiles_kernel_t
328 327
329 SELinux transitions the daemon's security 328 SELinux transitions the daemon's security ID to the module's security ID
330 based on a rule of this form in the polic 329 based on a rule of this form in the policy::
331 330
332 type_transition <daemon's-ID> kernel_t 331 type_transition <daemon's-ID> kernel_t : process <module's-ID>;
333 332
334 For instance:: 333 For instance::
335 334
336 type_transition cachefilesd_t kernel_t 335 type_transition cachefilesd_t kernel_t : process cachefiles_kernel_t;
337 336
338 337
339 The module's security ID gives it permission t 338 The module's security ID gives it permission to create, move and remove files
340 and directories in the cache, to find and acce 339 and directories in the cache, to find and access directories and files in the
341 cache, to set and access extended attributes o 340 cache, to set and access extended attributes on cache objects, and to read and
342 write files in the cache. 341 write files in the cache.
343 342
344 The daemon's security ID gives it only a very 343 The daemon's security ID gives it only a very restricted set of permissions: it
345 may scan directories, stat files and erase fil 344 may scan directories, stat files and erase files and directories. It may
346 not read or write files in the cache, and so i 345 not read or write files in the cache, and so it is precluded from accessing the
347 data cached therein; nor is it permitted to cr 346 data cached therein; nor is it permitted to create new files in the cache.
348 347
349 348
350 There are policy source files available in: 349 There are policy source files available in:
351 350
352 https://people.redhat.com/~dhowells/fs 351 https://people.redhat.com/~dhowells/fscache/cachefilesd-0.8.tar.bz2
353 352
354 and later versions. In that tarball, see the 353 and later versions. In that tarball, see the files::
355 354
356 cachefilesd.te 355 cachefilesd.te
357 cachefilesd.fc 356 cachefilesd.fc
358 cachefilesd.if 357 cachefilesd.if
359 358
360 They are built and installed directly by the R 359 They are built and installed directly by the RPM.
361 360
362 If a non-RPM based system is being used, then 361 If a non-RPM based system is being used, then copy the above files to their own
363 directory and run:: 362 directory and run::
364 363
365 make -f /usr/share/selinux/devel/Makef 364 make -f /usr/share/selinux/devel/Makefile
366 semodule -i cachefilesd.pp 365 semodule -i cachefilesd.pp
367 366
368 You will need checkpolicy and selinux-policy-d 367 You will need checkpolicy and selinux-policy-devel installed prior to the
369 build. 368 build.
370 369
371 370
372 By default, the cache is located in /var/fscac 371 By default, the cache is located in /var/fscache, but if it is desirable that
373 it should be elsewhere, than either the above 372 it should be elsewhere, than either the above policy files must be altered, or
374 an auxiliary policy must be installed to label 373 an auxiliary policy must be installed to label the alternate location of the
375 cache. 374 cache.
376 375
377 For instructions on how to add an auxiliary po 376 For instructions on how to add an auxiliary policy to enable the cache to be
378 located elsewhere when SELinux is in enforcing 377 located elsewhere when SELinux is in enforcing mode, please see::
379 378
380 /usr/share/doc/cachefilesd-*/move-cach 379 /usr/share/doc/cachefilesd-*/move-cache.txt
381 380
382 When the cachefilesd rpm is installed; alterna 381 When the cachefilesd rpm is installed; alternatively, the document can be found
383 in the sources. 382 in the sources.
384 383
385 384
386 A Note on Security 385 A Note on Security
387 ================== 386 ==================
388 387
389 CacheFiles makes use of the split security in 388 CacheFiles makes use of the split security in the task_struct. It allocates
390 its own task_security structure, and redirects 389 its own task_security structure, and redirects current->cred to point to it
391 when it acts on behalf of another process, in 390 when it acts on behalf of another process, in that process's context.
392 391
393 The reason it does this is that it calls vfs_m 392 The reason it does this is that it calls vfs_mkdir() and suchlike rather than
394 bypassing security and calling inode ops direc 393 bypassing security and calling inode ops directly. Therefore the VFS and LSM
395 may deny the CacheFiles access to the cache da 394 may deny the CacheFiles access to the cache data because under some
396 circumstances the caching code is running in t 395 circumstances the caching code is running in the security context of whatever
397 process issued the original syscall on the net 396 process issued the original syscall on the netfs.
398 397
399 Furthermore, should CacheFiles create a file o 398 Furthermore, should CacheFiles create a file or directory, the security
400 parameters with that object is created (UID, G 399 parameters with that object is created (UID, GID, security label) would be
401 derived from that process that issued the syst 400 derived from that process that issued the system call, thus potentially
402 preventing other processes from accessing the 401 preventing other processes from accessing the cache - including CacheFiles's
403 cache management daemon (cachefilesd). 402 cache management daemon (cachefilesd).
404 403
405 What is required is to temporarily override th 404 What is required is to temporarily override the security of the process that
406 issued the system call. We can't, however, ju 405 issued the system call. We can't, however, just do an in-place change of the
407 security data as that affects the process as a 406 security data as that affects the process as an object, not just as a subject.
408 This means it may lose signals or ptrace event 407 This means it may lose signals or ptrace events for example, and affects what
409 the process looks like in /proc. 408 the process looks like in /proc.
410 409
411 So CacheFiles makes use of a logical split in 410 So CacheFiles makes use of a logical split in the security between the
412 objective security (task->real_cred) and the s 411 objective security (task->real_cred) and the subjective security (task->cred).
413 The objective security holds the intrinsic sec 412 The objective security holds the intrinsic security properties of a process and
414 is never overridden. This is what appears in 413 is never overridden. This is what appears in /proc, and is what is used when a
415 process is the target of an operation by some 414 process is the target of an operation by some other process (SIGKILL for
416 example). 415 example).
417 416
418 The subjective security holds the active secur 417 The subjective security holds the active security properties of a process, and
419 may be overridden. This is not seen externall !! 418 may be overridden. This is not seen externally, and is used whan a process
420 acts upon another object, for example SIGKILLi 419 acts upon another object, for example SIGKILLing another process or opening a
421 file. 420 file.
422 421
423 LSM hooks exist that allow SELinux (or Smack o 422 LSM hooks exist that allow SELinux (or Smack or whatever) to reject a request
424 for CacheFiles to run in a context of a specif 423 for CacheFiles to run in a context of a specific security label, or to create
425 files and directories with another security la 424 files and directories with another security label.
426 425
427 426
428 Statistical Information 427 Statistical Information
429 ======================= 428 =======================
430 429
431 If FS-Cache is compiled with the following opt 430 If FS-Cache is compiled with the following option enabled::
432 431
433 CONFIG_CACHEFILES_HISTOGRAM=y 432 CONFIG_CACHEFILES_HISTOGRAM=y
434 433
435 then it will gather certain statistics and dis 434 then it will gather certain statistics and display them through a proc file.
436 435
437 /proc/fs/cachefiles/histogram 436 /proc/fs/cachefiles/histogram
438 437
439 :: 438 ::
440 439
441 cat /proc/fs/cachefiles/histogram 440 cat /proc/fs/cachefiles/histogram
442 JIFS SECS LOOKUPS MKDIRS CREATE 441 JIFS SECS LOOKUPS MKDIRS CREATES
443 ===== ===== ========= ========= ====== 442 ===== ===== ========= ========= =========
444 443
445 This shows the breakdown of the number of 444 This shows the breakdown of the number of times each amount of time
446 between 0 jiffies and HZ-1 jiffies a vari 445 between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The
447 columns are as follows: 446 columns are as follows:
448 447
449 ======= ====================== 448 ======= =======================================================
450 COLUMN TIME MEASUREMENT 449 COLUMN TIME MEASUREMENT
451 ======= ====================== 450 ======= =======================================================
452 LOOKUPS Length of time to perf 451 LOOKUPS Length of time to perform a lookup on the backing fs
453 MKDIRS Length of time to perf 452 MKDIRS Length of time to perform a mkdir on the backing fs
454 CREATES Length of time to perf 453 CREATES Length of time to perform a create on the backing fs
455 ======= ====================== 454 ======= =======================================================
456 455
457 Each row shows the number of events that 456 Each row shows the number of events that took a particular range of times.
458 Each step is 1 jiffy in size. The JIFS c 457 Each step is 1 jiffy in size. The JIFS column indicates the particular
459 jiffy range covered, and the SECS field t 458 jiffy range covered, and the SECS field the equivalent number of seconds.
460 459
461 460
462 Debugging 461 Debugging
463 ========= 462 =========
464 463
465 If CONFIG_CACHEFILES_DEBUG is enabled, the Cac 464 If CONFIG_CACHEFILES_DEBUG is enabled, the CacheFiles facility can have runtime
466 debugging enabled by adjusting the value in:: 465 debugging enabled by adjusting the value in::
467 466
468 /sys/module/cachefiles/parameters/debu 467 /sys/module/cachefiles/parameters/debug
469 468
470 This is a bitmask of debugging streams to enab 469 This is a bitmask of debugging streams to enable:
471 470
472 ======= ======= ====================== 471 ======= ======= =============================== =======================
473 BIT VALUE STREAM 472 BIT VALUE STREAM POINT
474 ======= ======= ====================== 473 ======= ======= =============================== =======================
475 0 1 General 474 0 1 General Function entry trace
476 1 2 475 1 2 Function exit trace
477 2 4 476 2 4 General
478 ======= ======= ====================== 477 ======= ======= =============================== =======================
479 478
480 The appropriate set of values should be OR'd t 479 The appropriate set of values should be OR'd together and the result written to
481 the control file. For example:: 480 the control file. For example::
482 481
483 echo $((1|4|8)) >/sys/module/cachefile 482 echo $((1|4|8)) >/sys/module/cachefiles/parameters/debug
484 483
485 will turn on all function entry debugging. 484 will turn on all function entry debugging.
486 <<
487 <<
488 On-demand Read <<
489 ============== <<
490 <<
491 When working in its original mode, CacheFiles <<
492 remote networking fs - while in on-demand read <<
493 scenario where on-demand read semantics are ne <<
494 distribution. <<
495 <<
496 The essential difference between these two mod <<
497 occurs: In the original mode, the netfs will f <<
498 server and then write it to the cache file; in <<
499 the data and writing it into the cache is dele <<
500 <<
501 ``CONFIG_CACHEFILES_ONDEMAND`` should be enabl <<
502 <<
503 <<
504 Protocol Communication <<
505 ---------------------- <<
506 <<
507 The on-demand read mode uses a simple protocol <<
508 and user daemon. The protocol can be modeled a <<
509 <<
510 kernel --[request]--> user daemon --[r <<
511 <<
512 CacheFiles will send requests to the user daem <<
513 should poll the devnode ('/dev/cachefiles') to <<
514 request to be processed. A POLLIN event will <<
515 request. <<
516 <<
517 The user daemon then reads the devnode to fetc <<
518 be noted that each read only gets one request. <<
519 the request, the user daemon should write the <<
520 <<
521 Each request starts with a message header of t <<
522 <<
523 struct cachefiles_msg { <<
524 __u32 msg_id; <<
525 __u32 opcode; <<
526 __u32 len; <<
527 __u32 object_id; <<
528 __u8 data[]; <<
529 }; <<
530 <<
531 where: <<
532 <<
533 * ``msg_id`` is a unique ID identifyin <<
534 requests. <<
535 <<
536 * ``opcode`` indicates the type of thi <<
537 <<
538 * ``object_id`` is a unique ID identif <<
539 <<
540 * ``data`` indicates the payload of th <<
541 <<
542 * ``len`` indicates the whole length o <<
543 header and following type-specific p <<
544 <<
545 <<
546 Turning on On-demand Mode <<
547 ------------------------- <<
548 <<
549 An optional parameter becomes available to the <<
550 <<
551 bind [ondemand] <<
552 <<
553 When the "bind" command is given no argument, <<
554 When it is given the "ondemand" argument, i.e. <<
555 mode will be enabled. <<
556 <<
557 <<
558 The OPEN Request <<
559 ---------------- <<
560 <<
561 When the netfs opens a cache file for the firs <<
562 CACHEFILES_OP_OPEN opcode, a.k.a an OPEN reque <<
563 daemon. The payload format is of the form:: <<
564 <<
565 struct cachefiles_open { <<
566 __u32 volume_key_size; <<
567 __u32 cookie_key_size; <<
568 __u32 fd; <<
569 __u32 flags; <<
570 __u8 data[]; <<
571 }; <<
572 <<
573 where: <<
574 <<
575 * ``data`` contains the volume_key fol <<
576 The volume key is a NUL-terminated s <<
577 data. <<
578 <<
579 * ``volume_key_size`` indicates the si <<
580 <<
581 * ``cookie_key_size`` indicates the si <<
582 <<
583 * ``fd`` indicates an anonymous fd ref <<
584 which the user daemon can perform wr <<
585 cache file. <<
586 <<
587 <<
588 The user daemon can use the given (volume_key, <<
589 the requested cache file. With the given anon <<
590 fetch the data and write it to the cache file <<
591 kernel has not triggered a cache miss yet. <<
592 <<
593 Be noted that each cache file has a unique obj <<
594 anonymous fds. The user daemon may duplicate <<
595 anonymous fd indicated by the @fd field throug <<
596 be mapped to multiple anonymous fds, while the <<
597 maintain the mapping. <<
598 <<
599 When implementing a user daemon, please be car <<
600 ``/proc/sys/fs/nr_open`` and ``/proc/sys/fs/fi <<
601 be huge since they're related to the number of <<
602 open files of each individual filesystem. <<
603 <<
604 The user daemon should reply the OPEN request <<
605 open) command on the devnode:: <<
606 <<
607 copen <msg_id>,<cache_size> <<
608 <<
609 where: <<
610 <<
611 * ``msg_id`` must match the msg_id fie <<
612 <<
613 * When >= 0, ``cache_size`` indicates <<
614 when < 0, ``cache_size`` indicates a <<
615 user daemon. <<
616 <<
617 <<
618 The CLOSE Request <<
619 ----------------- <<
620 <<
621 When a cookie withdrawn, a CLOSE request (opco <<
622 sent to the user daemon. This tells the user <<
623 associated with the given object_id. The CLOS <<
624 and shouldn't be replied. <<
625 <<
626 <<
627 The READ Request <<
628 ---------------- <<
629 <<
630 When a cache miss is encountered in on-demand <<
631 READ request (opcode CACHEFILES_OP_READ) to th <<
632 daemon to fetch the contents of the requested <<
633 form:: <<
634 <<
635 struct cachefiles_read { <<
636 __u64 off; <<
637 __u64 len; <<
638 }; <<
639 <<
640 where: <<
641 <<
642 * ``off`` indicates the starting offse <<
643 <<
644 * ``len`` indicates the length of the <<
645 <<
646 <<
647 When it receives a READ request, the user daem <<
648 and write it to the cache file identified by o <<
649 <<
650 When it has finished processing the READ reque <<
651 by using the CACHEFILES_IOC_READ_COMPLETE ioct <<
652 associated with the object_id given in the REA <<
653 form:: <<
654 <<
655 ioctl(fd, CACHEFILES_IOC_READ_COMPLETE <<
656 <<
657 where: <<
658 <<
659 * ``fd`` is one of the anonymous fds a <<
660 given. <<
661 <<
662 * ``msg_id`` must match the msg_id fie <<
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.