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1da177e4 LT |
1 | The text below describes the locking rules for VFS-related methods. |
2 | It is (believed to be) up-to-date. *Please*, if you change anything in | |
3 | prototypes or locking protocols - update this file. And update the relevant | |
4 | instances in the tree, don't leave that to maintainers of filesystems/devices/ | |
5 | etc. At the very least, put the list of dubious cases in the end of this file. | |
6 | Don't turn it into log - maintainers of out-of-the-tree code are supposed to | |
7 | be able to use diff(1). | |
8 | Thing currently missing here: socket operations. Alexey? | |
9 | ||
10 | --------------------------- dentry_operations -------------------------- | |
11 | prototypes: | |
12 | int (*d_revalidate)(struct dentry *, int); | |
13 | int (*d_hash) (struct dentry *, struct qstr *); | |
14 | int (*d_compare) (struct dentry *, struct qstr *, struct qstr *); | |
15 | int (*d_delete)(struct dentry *); | |
16 | void (*d_release)(struct dentry *); | |
17 | void (*d_iput)(struct dentry *, struct inode *); | |
c23fbb6b | 18 | char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen); |
1da177e4 LT |
19 | |
20 | locking rules: | |
21 | none have BKL | |
22 | dcache_lock rename_lock ->d_lock may block | |
23 | d_revalidate: no no no yes | |
24 | d_hash no no no yes | |
25 | d_compare: no yes no no | |
26 | d_delete: yes no yes no | |
27 | d_release: no no no yes | |
28 | d_iput: no no no yes | |
c23fbb6b | 29 | d_dname: no no no no |
1da177e4 LT |
30 | |
31 | --------------------------- inode_operations --------------------------- | |
32 | prototypes: | |
33 | int (*create) (struct inode *,struct dentry *,int, struct nameidata *); | |
34 | struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid | |
35 | ata *); | |
36 | int (*link) (struct dentry *,struct inode *,struct dentry *); | |
37 | int (*unlink) (struct inode *,struct dentry *); | |
38 | int (*symlink) (struct inode *,struct dentry *,const char *); | |
39 | int (*mkdir) (struct inode *,struct dentry *,int); | |
40 | int (*rmdir) (struct inode *,struct dentry *); | |
41 | int (*mknod) (struct inode *,struct dentry *,int,dev_t); | |
42 | int (*rename) (struct inode *, struct dentry *, | |
43 | struct inode *, struct dentry *); | |
44 | int (*readlink) (struct dentry *, char __user *,int); | |
45 | int (*follow_link) (struct dentry *, struct nameidata *); | |
46 | void (*truncate) (struct inode *); | |
47 | int (*permission) (struct inode *, int, struct nameidata *); | |
48 | int (*setattr) (struct dentry *, struct iattr *); | |
49 | int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *); | |
50 | int (*setxattr) (struct dentry *, const char *,const void *,size_t,int); | |
51 | ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t); | |
52 | ssize_t (*listxattr) (struct dentry *, char *, size_t); | |
53 | int (*removexattr) (struct dentry *, const char *); | |
54 | ||
55 | locking rules: | |
56 | all may block, none have BKL | |
a7bc02f4 | 57 | i_mutex(inode) |
1da177e4 LT |
58 | lookup: yes |
59 | create: yes | |
60 | link: yes (both) | |
61 | mknod: yes | |
62 | symlink: yes | |
63 | mkdir: yes | |
64 | unlink: yes (both) | |
65 | rmdir: yes (both) (see below) | |
66 | rename: yes (all) (see below) | |
67 | readlink: no | |
68 | follow_link: no | |
69 | truncate: yes (see below) | |
70 | setattr: yes | |
71 | permission: no | |
72 | getattr: no | |
73 | setxattr: yes | |
74 | getxattr: no | |
75 | listxattr: no | |
76 | removexattr: yes | |
a7bc02f4 | 77 | Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on |
1da177e4 LT |
78 | victim. |
79 | cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem. | |
80 | ->truncate() is never called directly - it's a callback, not a | |
81 | method. It's called by vmtruncate() - library function normally used by | |
82 | ->setattr(). Locking information above applies to that call (i.e. is | |
83 | inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been | |
84 | passed). | |
85 | ||
86 | See Documentation/filesystems/directory-locking for more detailed discussion | |
87 | of the locking scheme for directory operations. | |
88 | ||
89 | --------------------------- super_operations --------------------------- | |
90 | prototypes: | |
91 | struct inode *(*alloc_inode)(struct super_block *sb); | |
92 | void (*destroy_inode)(struct inode *); | |
1da177e4 LT |
93 | void (*dirty_inode) (struct inode *); |
94 | int (*write_inode) (struct inode *, int); | |
1da177e4 LT |
95 | void (*drop_inode) (struct inode *); |
96 | void (*delete_inode) (struct inode *); | |
97 | void (*put_super) (struct super_block *); | |
98 | void (*write_super) (struct super_block *); | |
99 | int (*sync_fs)(struct super_block *sb, int wait); | |
100 | void (*write_super_lockfs) (struct super_block *); | |
101 | void (*unlockfs) (struct super_block *); | |
726c3342 | 102 | int (*statfs) (struct dentry *, struct kstatfs *); |
1da177e4 LT |
103 | int (*remount_fs) (struct super_block *, int *, char *); |
104 | void (*clear_inode) (struct inode *); | |
105 | void (*umount_begin) (struct super_block *); | |
106 | int (*show_options)(struct seq_file *, struct vfsmount *); | |
107 | ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t); | |
108 | ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t); | |
109 | ||
110 | locking rules: | |
111 | All may block. | |
112 | BKL s_lock s_umount | |
113 | alloc_inode: no no no | |
114 | destroy_inode: no | |
1da177e4 LT |
115 | dirty_inode: no (must not sleep) |
116 | write_inode: no | |
1da177e4 LT |
117 | drop_inode: no !!!inode_lock!!! |
118 | delete_inode: no | |
119 | put_super: yes yes no | |
120 | write_super: no yes read | |
121 | sync_fs: no no read | |
122 | write_super_lockfs: ? | |
123 | unlockfs: ? | |
124 | statfs: no no no | |
70888bd5 | 125 | remount_fs: yes yes maybe (see below) |
1da177e4 LT |
126 | clear_inode: no |
127 | umount_begin: yes no no | |
128 | show_options: no (vfsmount->sem) | |
129 | quota_read: no no no (see below) | |
130 | quota_write: no no no (see below) | |
131 | ||
1da177e4 LT |
132 | ->remount_fs() will have the s_umount lock if it's already mounted. |
133 | When called from get_sb_single, it does NOT have the s_umount lock. | |
134 | ->quota_read() and ->quota_write() functions are both guaranteed to | |
135 | be the only ones operating on the quota file by the quota code (via | |
136 | dqio_sem) (unless an admin really wants to screw up something and | |
137 | writes to quota files with quotas on). For other details about locking | |
138 | see also dquot_operations section. | |
139 | ||
140 | --------------------------- file_system_type --------------------------- | |
141 | prototypes: | |
5d8b2ebf JC |
142 | int (*get_sb) (struct file_system_type *, int, |
143 | const char *, void *, struct vfsmount *); | |
1da177e4 LT |
144 | void (*kill_sb) (struct super_block *); |
145 | locking rules: | |
146 | may block BKL | |
147 | get_sb yes yes | |
148 | kill_sb yes yes | |
149 | ||
454e2398 DH |
150 | ->get_sb() returns error or 0 with locked superblock attached to the vfsmount |
151 | (exclusive on ->s_umount). | |
1da177e4 LT |
152 | ->kill_sb() takes a write-locked superblock, does all shutdown work on it, |
153 | unlocks and drops the reference. | |
154 | ||
155 | --------------------------- address_space_operations -------------------------- | |
156 | prototypes: | |
157 | int (*writepage)(struct page *page, struct writeback_control *wbc); | |
158 | int (*readpage)(struct file *, struct page *); | |
159 | int (*sync_page)(struct page *); | |
160 | int (*writepages)(struct address_space *, struct writeback_control *); | |
161 | int (*set_page_dirty)(struct page *page); | |
162 | int (*readpages)(struct file *filp, struct address_space *mapping, | |
163 | struct list_head *pages, unsigned nr_pages); | |
164 | int (*prepare_write)(struct file *, struct page *, unsigned, unsigned); | |
165 | int (*commit_write)(struct file *, struct page *, unsigned, unsigned); | |
166 | sector_t (*bmap)(struct address_space *, sector_t); | |
167 | int (*invalidatepage) (struct page *, unsigned long); | |
168 | int (*releasepage) (struct page *, int); | |
169 | int (*direct_IO)(int, struct kiocb *, const struct iovec *iov, | |
170 | loff_t offset, unsigned long nr_segs); | |
e3db7691 | 171 | int (*launder_page) (struct page *); |
1da177e4 LT |
172 | |
173 | locking rules: | |
174 | All except set_page_dirty may block | |
175 | ||
afddba49 | 176 | BKL PageLocked(page) i_sem |
1da177e4 LT |
177 | writepage: no yes, unlocks (see below) |
178 | readpage: no yes, unlocks | |
179 | sync_page: no maybe | |
180 | writepages: no | |
181 | set_page_dirty no no | |
182 | readpages: no | |
afddba49 NP |
183 | prepare_write: no yes yes |
184 | commit_write: no yes yes | |
185 | write_begin: no locks the page yes | |
186 | write_end: no yes, unlocks yes | |
187 | perform_write: no n/a yes | |
1da177e4 LT |
188 | bmap: yes |
189 | invalidatepage: no yes | |
190 | releasepage: no yes | |
191 | direct_IO: no | |
e3db7691 | 192 | launder_page: no yes |
1da177e4 LT |
193 | |
194 | ->prepare_write(), ->commit_write(), ->sync_page() and ->readpage() | |
195 | may be called from the request handler (/dev/loop). | |
196 | ||
197 | ->readpage() unlocks the page, either synchronously or via I/O | |
198 | completion. | |
199 | ||
200 | ->readpages() populates the pagecache with the passed pages and starts | |
201 | I/O against them. They come unlocked upon I/O completion. | |
202 | ||
203 | ->writepage() is used for two purposes: for "memory cleansing" and for | |
204 | "sync". These are quite different operations and the behaviour may differ | |
205 | depending upon the mode. | |
206 | ||
207 | If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then | |
208 | it *must* start I/O against the page, even if that would involve | |
209 | blocking on in-progress I/O. | |
210 | ||
211 | If writepage is called for memory cleansing (sync_mode == | |
212 | WBC_SYNC_NONE) then its role is to get as much writeout underway as | |
213 | possible. So writepage should try to avoid blocking against | |
214 | currently-in-progress I/O. | |
215 | ||
216 | If the filesystem is not called for "sync" and it determines that it | |
217 | would need to block against in-progress I/O to be able to start new I/O | |
218 | against the page the filesystem should redirty the page with | |
219 | redirty_page_for_writepage(), then unlock the page and return zero. | |
220 | This may also be done to avoid internal deadlocks, but rarely. | |
221 | ||
3a4fa0a2 | 222 | If the filesystem is called for sync then it must wait on any |
1da177e4 LT |
223 | in-progress I/O and then start new I/O. |
224 | ||
2054606a ND |
225 | The filesystem should unlock the page synchronously, before returning to the |
226 | caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE | |
227 | value. WRITEPAGE_ACTIVATE means that page cannot really be written out | |
228 | currently, and VM should stop calling ->writepage() on this page for some | |
229 | time. VM does this by moving page to the head of the active list, hence the | |
230 | name. | |
1da177e4 LT |
231 | |
232 | Unless the filesystem is going to redirty_page_for_writepage(), unlock the page | |
233 | and return zero, writepage *must* run set_page_writeback() against the page, | |
234 | followed by unlocking it. Once set_page_writeback() has been run against the | |
235 | page, write I/O can be submitted and the write I/O completion handler must run | |
236 | end_page_writeback() once the I/O is complete. If no I/O is submitted, the | |
237 | filesystem must run end_page_writeback() against the page before returning from | |
238 | writepage. | |
239 | ||
240 | That is: after 2.5.12, pages which are under writeout are *not* locked. Note, | |
241 | if the filesystem needs the page to be locked during writeout, that is ok, too, | |
242 | the page is allowed to be unlocked at any point in time between the calls to | |
243 | set_page_writeback() and end_page_writeback(). | |
244 | ||
245 | Note, failure to run either redirty_page_for_writepage() or the combination of | |
246 | set_page_writeback()/end_page_writeback() on a page submitted to writepage | |
247 | will leave the page itself marked clean but it will be tagged as dirty in the | |
248 | radix tree. This incoherency can lead to all sorts of hard-to-debug problems | |
249 | in the filesystem like having dirty inodes at umount and losing written data. | |
250 | ||
251 | ->sync_page() locking rules are not well-defined - usually it is called | |
252 | with lock on page, but that is not guaranteed. Considering the currently | |
253 | existing instances of this method ->sync_page() itself doesn't look | |
254 | well-defined... | |
255 | ||
256 | ->writepages() is used for periodic writeback and for syscall-initiated | |
257 | sync operations. The address_space should start I/O against at least | |
258 | *nr_to_write pages. *nr_to_write must be decremented for each page which is | |
259 | written. The address_space implementation may write more (or less) pages | |
260 | than *nr_to_write asks for, but it should try to be reasonably close. If | |
261 | nr_to_write is NULL, all dirty pages must be written. | |
262 | ||
263 | writepages should _only_ write pages which are present on | |
264 | mapping->io_pages. | |
265 | ||
266 | ->set_page_dirty() is called from various places in the kernel | |
267 | when the target page is marked as needing writeback. It may be called | |
268 | under spinlock (it cannot block) and is sometimes called with the page | |
269 | not locked. | |
270 | ||
271 | ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some | |
272 | filesystems and by the swapper. The latter will eventually go away. All | |
273 | instances do not actually need the BKL. Please, keep it that way and don't | |
274 | breed new callers. | |
275 | ||
276 | ->invalidatepage() is called when the filesystem must attempt to drop | |
277 | some or all of the buffers from the page when it is being truncated. It | |
278 | returns zero on success. If ->invalidatepage is zero, the kernel uses | |
279 | block_invalidatepage() instead. | |
280 | ||
281 | ->releasepage() is called when the kernel is about to try to drop the | |
282 | buffers from the page in preparation for freeing it. It returns zero to | |
283 | indicate that the buffers are (or may be) freeable. If ->releasepage is zero, | |
284 | the kernel assumes that the fs has no private interest in the buffers. | |
285 | ||
e3db7691 TM |
286 | ->launder_page() may be called prior to releasing a page if |
287 | it is still found to be dirty. It returns zero if the page was successfully | |
288 | cleaned, or an error value if not. Note that in order to prevent the page | |
289 | getting mapped back in and redirtied, it needs to be kept locked | |
290 | across the entire operation. | |
291 | ||
1da177e4 LT |
292 | Note: currently almost all instances of address_space methods are |
293 | using BKL for internal serialization and that's one of the worst sources | |
294 | of contention. Normally they are calling library functions (in fs/buffer.c) | |
295 | and pass foo_get_block() as a callback (on local block-based filesystems, | |
296 | indeed). BKL is not needed for library stuff and is usually taken by | |
297 | foo_get_block(). It's an overkill, since block bitmaps can be protected by | |
298 | internal fs locking and real critical areas are much smaller than the areas | |
299 | filesystems protect now. | |
300 | ||
301 | ----------------------- file_lock_operations ------------------------------ | |
302 | prototypes: | |
303 | void (*fl_insert)(struct file_lock *); /* lock insertion callback */ | |
304 | void (*fl_remove)(struct file_lock *); /* lock removal callback */ | |
305 | void (*fl_copy_lock)(struct file_lock *, struct file_lock *); | |
306 | void (*fl_release_private)(struct file_lock *); | |
307 | ||
308 | ||
309 | locking rules: | |
310 | BKL may block | |
311 | fl_insert: yes no | |
312 | fl_remove: yes no | |
313 | fl_copy_lock: yes no | |
314 | fl_release_private: yes yes | |
315 | ||
316 | ----------------------- lock_manager_operations --------------------------- | |
317 | prototypes: | |
318 | int (*fl_compare_owner)(struct file_lock *, struct file_lock *); | |
319 | void (*fl_notify)(struct file_lock *); /* unblock callback */ | |
320 | void (*fl_copy_lock)(struct file_lock *, struct file_lock *); | |
321 | void (*fl_release_private)(struct file_lock *); | |
322 | void (*fl_break)(struct file_lock *); /* break_lease callback */ | |
323 | ||
324 | locking rules: | |
325 | BKL may block | |
326 | fl_compare_owner: yes no | |
327 | fl_notify: yes no | |
328 | fl_copy_lock: yes no | |
329 | fl_release_private: yes yes | |
330 | fl_break: yes no | |
331 | ||
332 | Currently only NFSD and NLM provide instances of this class. None of the | |
333 | them block. If you have out-of-tree instances - please, show up. Locking | |
334 | in that area will change. | |
335 | --------------------------- buffer_head ----------------------------------- | |
336 | prototypes: | |
337 | void (*b_end_io)(struct buffer_head *bh, int uptodate); | |
338 | ||
339 | locking rules: | |
340 | called from interrupts. In other words, extreme care is needed here. | |
341 | bh is locked, but that's all warranties we have here. Currently only RAID1, | |
342 | highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices | |
343 | call this method upon the IO completion. | |
344 | ||
345 | --------------------------- block_device_operations ----------------------- | |
346 | prototypes: | |
347 | int (*open) (struct inode *, struct file *); | |
348 | int (*release) (struct inode *, struct file *); | |
349 | int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long); | |
350 | int (*media_changed) (struct gendisk *); | |
351 | int (*revalidate_disk) (struct gendisk *); | |
352 | ||
353 | locking rules: | |
354 | BKL bd_sem | |
355 | open: yes yes | |
356 | release: yes yes | |
357 | ioctl: yes no | |
358 | media_changed: no no | |
359 | revalidate_disk: no no | |
360 | ||
361 | The last two are called only from check_disk_change(). | |
362 | ||
363 | --------------------------- file_operations ------------------------------- | |
364 | prototypes: | |
365 | loff_t (*llseek) (struct file *, loff_t, int); | |
366 | ssize_t (*read) (struct file *, char __user *, size_t, loff_t *); | |
1da177e4 | 367 | ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *); |
027445c3 BP |
368 | ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t); |
369 | ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t); | |
1da177e4 LT |
370 | int (*readdir) (struct file *, void *, filldir_t); |
371 | unsigned int (*poll) (struct file *, struct poll_table_struct *); | |
372 | int (*ioctl) (struct inode *, struct file *, unsigned int, | |
373 | unsigned long); | |
374 | long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); | |
375 | long (*compat_ioctl) (struct file *, unsigned int, unsigned long); | |
376 | int (*mmap) (struct file *, struct vm_area_struct *); | |
377 | int (*open) (struct inode *, struct file *); | |
378 | int (*flush) (struct file *); | |
379 | int (*release) (struct inode *, struct file *); | |
380 | int (*fsync) (struct file *, struct dentry *, int datasync); | |
381 | int (*aio_fsync) (struct kiocb *, int datasync); | |
382 | int (*fasync) (int, struct file *, int); | |
383 | int (*lock) (struct file *, int, struct file_lock *); | |
384 | ssize_t (*readv) (struct file *, const struct iovec *, unsigned long, | |
385 | loff_t *); | |
386 | ssize_t (*writev) (struct file *, const struct iovec *, unsigned long, | |
387 | loff_t *); | |
388 | ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, | |
389 | void __user *); | |
390 | ssize_t (*sendpage) (struct file *, struct page *, int, size_t, | |
391 | loff_t *, int); | |
392 | unsigned long (*get_unmapped_area)(struct file *, unsigned long, | |
393 | unsigned long, unsigned long, unsigned long); | |
394 | int (*check_flags)(int); | |
395 | int (*dir_notify)(struct file *, unsigned long); | |
396 | }; | |
397 | ||
398 | locking rules: | |
399 | All except ->poll() may block. | |
400 | BKL | |
401 | llseek: no (see below) | |
402 | read: no | |
403 | aio_read: no | |
404 | write: no | |
405 | aio_write: no | |
406 | readdir: no | |
407 | poll: no | |
408 | ioctl: yes (see below) | |
409 | unlocked_ioctl: no (see below) | |
410 | compat_ioctl: no | |
411 | mmap: no | |
412 | open: maybe (see below) | |
413 | flush: no | |
414 | release: no | |
415 | fsync: no (see below) | |
416 | aio_fsync: no | |
417 | fasync: yes (see below) | |
418 | lock: yes | |
419 | readv: no | |
420 | writev: no | |
421 | sendfile: no | |
422 | sendpage: no | |
423 | get_unmapped_area: no | |
424 | check_flags: no | |
425 | dir_notify: no | |
426 | ||
427 | ->llseek() locking has moved from llseek to the individual llseek | |
428 | implementations. If your fs is not using generic_file_llseek, you | |
429 | need to acquire and release the appropriate locks in your ->llseek(). | |
430 | For many filesystems, it is probably safe to acquire the inode | |
431 | semaphore. Note some filesystems (i.e. remote ones) provide no | |
432 | protection for i_size so you will need to use the BKL. | |
433 | ||
434 | ->open() locking is in-transit: big lock partially moved into the methods. | |
435 | The only exception is ->open() in the instances of file_operations that never | |
436 | end up in ->i_fop/->proc_fops, i.e. ones that belong to character devices | |
437 | (chrdev_open() takes lock before replacing ->f_op and calling the secondary | |
438 | method. As soon as we fix the handling of module reference counters all | |
439 | instances of ->open() will be called without the BKL. | |
440 | ||
441 | Note: ext2_release() was *the* source of contention on fs-intensive | |
442 | loads and dropping BKL on ->release() helps to get rid of that (we still | |
443 | grab BKL for cases when we close a file that had been opened r/w, but that | |
444 | can and should be done using the internal locking with smaller critical areas). | |
445 | Current worst offender is ext2_get_block()... | |
446 | ||
447 | ->fasync() is a mess. This area needs a big cleanup and that will probably | |
448 | affect locking. | |
449 | ||
450 | ->readdir() and ->ioctl() on directories must be changed. Ideally we would | |
451 | move ->readdir() to inode_operations and use a separate method for directory | |
452 | ->ioctl() or kill the latter completely. One of the problems is that for | |
453 | anything that resembles union-mount we won't have a struct file for all | |
454 | components. And there are other reasons why the current interface is a mess... | |
455 | ||
456 | ->ioctl() on regular files is superceded by the ->unlocked_ioctl() that | |
457 | doesn't take the BKL. | |
458 | ||
459 | ->read on directories probably must go away - we should just enforce -EISDIR | |
460 | in sys_read() and friends. | |
461 | ||
a7bc02f4 | 462 | ->fsync() has i_mutex on inode. |
1da177e4 LT |
463 | |
464 | --------------------------- dquot_operations ------------------------------- | |
465 | prototypes: | |
466 | int (*initialize) (struct inode *, int); | |
467 | int (*drop) (struct inode *); | |
468 | int (*alloc_space) (struct inode *, qsize_t, int); | |
469 | int (*alloc_inode) (const struct inode *, unsigned long); | |
470 | int (*free_space) (struct inode *, qsize_t); | |
471 | int (*free_inode) (const struct inode *, unsigned long); | |
472 | int (*transfer) (struct inode *, struct iattr *); | |
473 | int (*write_dquot) (struct dquot *); | |
474 | int (*acquire_dquot) (struct dquot *); | |
475 | int (*release_dquot) (struct dquot *); | |
476 | int (*mark_dirty) (struct dquot *); | |
477 | int (*write_info) (struct super_block *, int); | |
478 | ||
479 | These operations are intended to be more or less wrapping functions that ensure | |
480 | a proper locking wrt the filesystem and call the generic quota operations. | |
481 | ||
482 | What filesystem should expect from the generic quota functions: | |
483 | ||
484 | FS recursion Held locks when called | |
485 | initialize: yes maybe dqonoff_sem | |
486 | drop: yes - | |
487 | alloc_space: ->mark_dirty() - | |
488 | alloc_inode: ->mark_dirty() - | |
489 | free_space: ->mark_dirty() - | |
490 | free_inode: ->mark_dirty() - | |
491 | transfer: yes - | |
492 | write_dquot: yes dqonoff_sem or dqptr_sem | |
493 | acquire_dquot: yes dqonoff_sem or dqptr_sem | |
494 | release_dquot: yes dqonoff_sem or dqptr_sem | |
495 | mark_dirty: no - | |
496 | write_info: yes dqonoff_sem | |
497 | ||
498 | FS recursion means calling ->quota_read() and ->quota_write() from superblock | |
499 | operations. | |
500 | ||
501 | ->alloc_space(), ->alloc_inode(), ->free_space(), ->free_inode() are called | |
502 | only directly by the filesystem and do not call any fs functions only | |
503 | the ->mark_dirty() operation. | |
504 | ||
505 | More details about quota locking can be found in fs/dquot.c. | |
506 | ||
507 | --------------------------- vm_operations_struct ----------------------------- | |
508 | prototypes: | |
509 | void (*open)(struct vm_area_struct*); | |
510 | void (*close)(struct vm_area_struct*); | |
d0217ac0 | 511 | int (*fault)(struct vm_area_struct*, struct vm_fault *); |
ed2f2f9b | 512 | int (*page_mkwrite)(struct vm_area_struct *, struct page *); |
1da177e4 LT |
513 | |
514 | locking rules: | |
ed2f2f9b | 515 | BKL mmap_sem PageLocked(page) |
1da177e4 LT |
516 | open: no yes |
517 | close: no yes | |
54cb8821 | 518 | fault: no yes |
ed2f2f9b MF |
519 | page_mkwrite: no yes no |
520 | ||
521 | ->page_mkwrite() is called when a previously read-only page is | |
522 | about to become writeable. The file system is responsible for | |
523 | protecting against truncate races. Once appropriate action has been | |
524 | taking to lock out truncate, the page range should be verified to be | |
525 | within i_size. The page mapping should also be checked that it is not | |
526 | NULL. | |
1da177e4 LT |
527 | |
528 | ================================================================================ | |
529 | Dubious stuff | |
530 | ||
531 | (if you break something or notice that it is broken and do not fix it yourself | |
532 | - at least put it here) | |
533 | ||
534 | ipc/shm.c::shm_delete() - may need BKL. | |
535 | ->read() and ->write() in many drivers are (probably) missing BKL. |