Commit | Line | Data |
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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: | |
1da177e4 LT |
21 | dcache_lock rename_lock ->d_lock may block |
22 | d_revalidate: no no no yes | |
23 | d_hash no no no yes | |
24 | d_compare: no yes no no | |
25 | d_delete: yes no yes no | |
26 | d_release: no no no yes | |
27 | d_iput: no no no yes | |
c23fbb6b | 28 | d_dname: no no no no |
1da177e4 LT |
29 | |
30 | --------------------------- inode_operations --------------------------- | |
31 | prototypes: | |
32 | int (*create) (struct inode *,struct dentry *,int, struct nameidata *); | |
33 | struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid | |
34 | ata *); | |
35 | int (*link) (struct dentry *,struct inode *,struct dentry *); | |
36 | int (*unlink) (struct inode *,struct dentry *); | |
37 | int (*symlink) (struct inode *,struct dentry *,const char *); | |
38 | int (*mkdir) (struct inode *,struct dentry *,int); | |
39 | int (*rmdir) (struct inode *,struct dentry *); | |
40 | int (*mknod) (struct inode *,struct dentry *,int,dev_t); | |
41 | int (*rename) (struct inode *, struct dentry *, | |
42 | struct inode *, struct dentry *); | |
43 | int (*readlink) (struct dentry *, char __user *,int); | |
b83be6f2 CH |
44 | void * (*follow_link) (struct dentry *, struct nameidata *); |
45 | void (*put_link) (struct dentry *, struct nameidata *, void *); | |
1da177e4 LT |
46 | void (*truncate) (struct inode *); |
47 | int (*permission) (struct inode *, int, struct nameidata *); | |
b83be6f2 | 48 | int (*check_acl)(struct inode *, int); |
1da177e4 LT |
49 | int (*setattr) (struct dentry *, struct iattr *); |
50 | int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *); | |
51 | int (*setxattr) (struct dentry *, const char *,const void *,size_t,int); | |
52 | ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t); | |
53 | ssize_t (*listxattr) (struct dentry *, char *, size_t); | |
54 | int (*removexattr) (struct dentry *, const char *); | |
b83be6f2 CH |
55 | void (*truncate_range)(struct inode *, loff_t, loff_t); |
56 | long (*fallocate)(struct inode *inode, int mode, loff_t offset, loff_t len); | |
57 | int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len); | |
1da177e4 LT |
58 | |
59 | locking rules: | |
b83be6f2 | 60 | all may block |
a7bc02f4 | 61 | i_mutex(inode) |
1da177e4 LT |
62 | lookup: yes |
63 | create: yes | |
64 | link: yes (both) | |
65 | mknod: yes | |
66 | symlink: yes | |
67 | mkdir: yes | |
68 | unlink: yes (both) | |
69 | rmdir: yes (both) (see below) | |
70 | rename: yes (all) (see below) | |
71 | readlink: no | |
72 | follow_link: no | |
b83be6f2 | 73 | put_link: no |
1da177e4 LT |
74 | truncate: yes (see below) |
75 | setattr: yes | |
76 | permission: no | |
b83be6f2 | 77 | check_acl: no |
1da177e4 LT |
78 | getattr: no |
79 | setxattr: yes | |
80 | getxattr: no | |
81 | listxattr: no | |
82 | removexattr: yes | |
b83be6f2 CH |
83 | truncate_range: yes |
84 | fallocate: no | |
85 | fiemap: no | |
a7bc02f4 | 86 | Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on |
1da177e4 LT |
87 | victim. |
88 | cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem. | |
89 | ->truncate() is never called directly - it's a callback, not a | |
b83be6f2 | 90 | method. It's called by vmtruncate() - deprecated library function used by |
1da177e4 LT |
91 | ->setattr(). Locking information above applies to that call (i.e. is |
92 | inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been | |
93 | passed). | |
94 | ||
95 | See Documentation/filesystems/directory-locking for more detailed discussion | |
96 | of the locking scheme for directory operations. | |
97 | ||
98 | --------------------------- super_operations --------------------------- | |
99 | prototypes: | |
100 | struct inode *(*alloc_inode)(struct super_block *sb); | |
101 | void (*destroy_inode)(struct inode *); | |
1da177e4 | 102 | void (*dirty_inode) (struct inode *); |
b83be6f2 | 103 | int (*write_inode) (struct inode *, struct writeback_control *wbc); |
336fb3b9 AV |
104 | int (*drop_inode) (struct inode *); |
105 | void (*evict_inode) (struct inode *); | |
1da177e4 LT |
106 | void (*put_super) (struct super_block *); |
107 | void (*write_super) (struct super_block *); | |
108 | int (*sync_fs)(struct super_block *sb, int wait); | |
c4be0c1d TS |
109 | int (*freeze_fs) (struct super_block *); |
110 | int (*unfreeze_fs) (struct super_block *); | |
726c3342 | 111 | int (*statfs) (struct dentry *, struct kstatfs *); |
1da177e4 | 112 | int (*remount_fs) (struct super_block *, int *, char *); |
1da177e4 LT |
113 | void (*umount_begin) (struct super_block *); |
114 | int (*show_options)(struct seq_file *, struct vfsmount *); | |
115 | ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t); | |
116 | ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t); | |
b83be6f2 | 117 | int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t); |
1da177e4 LT |
118 | |
119 | locking rules: | |
336fb3b9 | 120 | All may block [not true, see below] |
7e325d3a CH |
121 | s_umount |
122 | alloc_inode: | |
123 | destroy_inode: | |
124 | dirty_inode: (must not sleep) | |
125 | write_inode: | |
126 | drop_inode: !!!inode_lock!!! | |
336fb3b9 | 127 | evict_inode: |
7e325d3a CH |
128 | put_super: write |
129 | write_super: read | |
130 | sync_fs: read | |
131 | freeze_fs: read | |
132 | unfreeze_fs: read | |
336fb3b9 AV |
133 | statfs: maybe(read) (see below) |
134 | remount_fs: write | |
7e325d3a CH |
135 | umount_begin: no |
136 | show_options: no (namespace_sem) | |
137 | quota_read: no (see below) | |
138 | quota_write: no (see below) | |
b83be6f2 | 139 | bdev_try_to_free_page: no (see below) |
1da177e4 | 140 | |
336fb3b9 AV |
141 | ->statfs() has s_umount (shared) when called by ustat(2) (native or |
142 | compat), but that's an accident of bad API; s_umount is used to pin | |
143 | the superblock down when we only have dev_t given us by userland to | |
144 | identify the superblock. Everything else (statfs(), fstatfs(), etc.) | |
145 | doesn't hold it when calling ->statfs() - superblock is pinned down | |
146 | by resolving the pathname passed to syscall. | |
1da177e4 LT |
147 | ->quota_read() and ->quota_write() functions are both guaranteed to |
148 | be the only ones operating on the quota file by the quota code (via | |
149 | dqio_sem) (unless an admin really wants to screw up something and | |
150 | writes to quota files with quotas on). For other details about locking | |
151 | see also dquot_operations section. | |
b83be6f2 CH |
152 | ->bdev_try_to_free_page is called from the ->releasepage handler of |
153 | the block device inode. See there for more details. | |
1da177e4 LT |
154 | |
155 | --------------------------- file_system_type --------------------------- | |
156 | prototypes: | |
5d8b2ebf JC |
157 | int (*get_sb) (struct file_system_type *, int, |
158 | const char *, void *, struct vfsmount *); | |
b83be6f2 CH |
159 | struct dentry *(*mount) (struct file_system_type *, int, |
160 | const char *, void *); | |
1da177e4 LT |
161 | void (*kill_sb) (struct super_block *); |
162 | locking rules: | |
b83be6f2 CH |
163 | may block |
164 | get_sb yes | |
165 | mount yes | |
166 | kill_sb yes | |
1da177e4 | 167 | |
454e2398 DH |
168 | ->get_sb() returns error or 0 with locked superblock attached to the vfsmount |
169 | (exclusive on ->s_umount). | |
b83be6f2 | 170 | ->mount() returns ERR_PTR or the root dentry. |
1da177e4 LT |
171 | ->kill_sb() takes a write-locked superblock, does all shutdown work on it, |
172 | unlocks and drops the reference. | |
173 | ||
174 | --------------------------- address_space_operations -------------------------- | |
175 | prototypes: | |
176 | int (*writepage)(struct page *page, struct writeback_control *wbc); | |
177 | int (*readpage)(struct file *, struct page *); | |
178 | int (*sync_page)(struct page *); | |
179 | int (*writepages)(struct address_space *, struct writeback_control *); | |
180 | int (*set_page_dirty)(struct page *page); | |
181 | int (*readpages)(struct file *filp, struct address_space *mapping, | |
182 | struct list_head *pages, unsigned nr_pages); | |
4e02ed4b NP |
183 | int (*write_begin)(struct file *, struct address_space *mapping, |
184 | loff_t pos, unsigned len, unsigned flags, | |
185 | struct page **pagep, void **fsdata); | |
186 | int (*write_end)(struct file *, struct address_space *mapping, | |
187 | loff_t pos, unsigned len, unsigned copied, | |
188 | struct page *page, void *fsdata); | |
1da177e4 LT |
189 | sector_t (*bmap)(struct address_space *, sector_t); |
190 | int (*invalidatepage) (struct page *, unsigned long); | |
191 | int (*releasepage) (struct page *, int); | |
6072d13c | 192 | void (*freepage)(struct page *); |
1da177e4 LT |
193 | int (*direct_IO)(int, struct kiocb *, const struct iovec *iov, |
194 | loff_t offset, unsigned long nr_segs); | |
b83be6f2 CH |
195 | int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **, |
196 | unsigned long *); | |
197 | int (*migratepage)(struct address_space *, struct page *, struct page *); | |
198 | int (*launder_page)(struct page *); | |
199 | int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long); | |
200 | int (*error_remove_page)(struct address_space *, struct page *); | |
1da177e4 LT |
201 | |
202 | locking rules: | |
6072d13c | 203 | All except set_page_dirty and freepage may block |
1da177e4 | 204 | |
b83be6f2 CH |
205 | PageLocked(page) i_mutex |
206 | writepage: yes, unlocks (see below) | |
207 | readpage: yes, unlocks | |
208 | sync_page: maybe | |
209 | writepages: | |
210 | set_page_dirty no | |
211 | readpages: | |
212 | write_begin: locks the page yes | |
213 | write_end: yes, unlocks yes | |
214 | bmap: | |
215 | invalidatepage: yes | |
216 | releasepage: yes | |
217 | freepage: yes | |
218 | direct_IO: | |
219 | get_xip_mem: maybe | |
220 | migratepage: yes (both) | |
221 | launder_page: yes | |
222 | is_partially_uptodate: yes | |
223 | error_remove_page: yes | |
1da177e4 | 224 | |
4e02ed4b | 225 | ->write_begin(), ->write_end(), ->sync_page() and ->readpage() |
1da177e4 LT |
226 | may be called from the request handler (/dev/loop). |
227 | ||
228 | ->readpage() unlocks the page, either synchronously or via I/O | |
229 | completion. | |
230 | ||
231 | ->readpages() populates the pagecache with the passed pages and starts | |
232 | I/O against them. They come unlocked upon I/O completion. | |
233 | ||
234 | ->writepage() is used for two purposes: for "memory cleansing" and for | |
235 | "sync". These are quite different operations and the behaviour may differ | |
236 | depending upon the mode. | |
237 | ||
238 | If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then | |
239 | it *must* start I/O against the page, even if that would involve | |
240 | blocking on in-progress I/O. | |
241 | ||
242 | If writepage is called for memory cleansing (sync_mode == | |
243 | WBC_SYNC_NONE) then its role is to get as much writeout underway as | |
244 | possible. So writepage should try to avoid blocking against | |
245 | currently-in-progress I/O. | |
246 | ||
247 | If the filesystem is not called for "sync" and it determines that it | |
248 | would need to block against in-progress I/O to be able to start new I/O | |
249 | against the page the filesystem should redirty the page with | |
250 | redirty_page_for_writepage(), then unlock the page and return zero. | |
251 | This may also be done to avoid internal deadlocks, but rarely. | |
252 | ||
3a4fa0a2 | 253 | If the filesystem is called for sync then it must wait on any |
1da177e4 LT |
254 | in-progress I/O and then start new I/O. |
255 | ||
2054606a ND |
256 | The filesystem should unlock the page synchronously, before returning to the |
257 | caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE | |
258 | value. WRITEPAGE_ACTIVATE means that page cannot really be written out | |
259 | currently, and VM should stop calling ->writepage() on this page for some | |
260 | time. VM does this by moving page to the head of the active list, hence the | |
261 | name. | |
1da177e4 LT |
262 | |
263 | Unless the filesystem is going to redirty_page_for_writepage(), unlock the page | |
264 | and return zero, writepage *must* run set_page_writeback() against the page, | |
265 | followed by unlocking it. Once set_page_writeback() has been run against the | |
266 | page, write I/O can be submitted and the write I/O completion handler must run | |
267 | end_page_writeback() once the I/O is complete. If no I/O is submitted, the | |
268 | filesystem must run end_page_writeback() against the page before returning from | |
269 | writepage. | |
270 | ||
271 | That is: after 2.5.12, pages which are under writeout are *not* locked. Note, | |
272 | if the filesystem needs the page to be locked during writeout, that is ok, too, | |
273 | the page is allowed to be unlocked at any point in time between the calls to | |
274 | set_page_writeback() and end_page_writeback(). | |
275 | ||
276 | Note, failure to run either redirty_page_for_writepage() or the combination of | |
277 | set_page_writeback()/end_page_writeback() on a page submitted to writepage | |
278 | will leave the page itself marked clean but it will be tagged as dirty in the | |
279 | radix tree. This incoherency can lead to all sorts of hard-to-debug problems | |
280 | in the filesystem like having dirty inodes at umount and losing written data. | |
281 | ||
282 | ->sync_page() locking rules are not well-defined - usually it is called | |
283 | with lock on page, but that is not guaranteed. Considering the currently | |
284 | existing instances of this method ->sync_page() itself doesn't look | |
285 | well-defined... | |
286 | ||
287 | ->writepages() is used for periodic writeback and for syscall-initiated | |
288 | sync operations. The address_space should start I/O against at least | |
289 | *nr_to_write pages. *nr_to_write must be decremented for each page which is | |
290 | written. The address_space implementation may write more (or less) pages | |
291 | than *nr_to_write asks for, but it should try to be reasonably close. If | |
292 | nr_to_write is NULL, all dirty pages must be written. | |
293 | ||
294 | writepages should _only_ write pages which are present on | |
295 | mapping->io_pages. | |
296 | ||
297 | ->set_page_dirty() is called from various places in the kernel | |
298 | when the target page is marked as needing writeback. It may be called | |
299 | under spinlock (it cannot block) and is sometimes called with the page | |
300 | not locked. | |
301 | ||
302 | ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some | |
b83be6f2 CH |
303 | filesystems and by the swapper. The latter will eventually go away. Please, |
304 | keep it that way and don't breed new callers. | |
1da177e4 LT |
305 | |
306 | ->invalidatepage() is called when the filesystem must attempt to drop | |
307 | some or all of the buffers from the page when it is being truncated. It | |
308 | returns zero on success. If ->invalidatepage is zero, the kernel uses | |
309 | block_invalidatepage() instead. | |
310 | ||
311 | ->releasepage() is called when the kernel is about to try to drop the | |
312 | buffers from the page in preparation for freeing it. It returns zero to | |
313 | indicate that the buffers are (or may be) freeable. If ->releasepage is zero, | |
314 | the kernel assumes that the fs has no private interest in the buffers. | |
315 | ||
6072d13c LT |
316 | ->freepage() is called when the kernel is done dropping the page |
317 | from the page cache. | |
318 | ||
e3db7691 TM |
319 | ->launder_page() may be called prior to releasing a page if |
320 | it is still found to be dirty. It returns zero if the page was successfully | |
321 | cleaned, or an error value if not. Note that in order to prevent the page | |
322 | getting mapped back in and redirtied, it needs to be kept locked | |
323 | across the entire operation. | |
324 | ||
1da177e4 LT |
325 | ----------------------- file_lock_operations ------------------------------ |
326 | prototypes: | |
1da177e4 LT |
327 | void (*fl_copy_lock)(struct file_lock *, struct file_lock *); |
328 | void (*fl_release_private)(struct file_lock *); | |
329 | ||
330 | ||
331 | locking rules: | |
b83be6f2 CH |
332 | file_lock_lock may block |
333 | fl_copy_lock: yes no | |
334 | fl_release_private: maybe no | |
1da177e4 LT |
335 | |
336 | ----------------------- lock_manager_operations --------------------------- | |
337 | prototypes: | |
338 | int (*fl_compare_owner)(struct file_lock *, struct file_lock *); | |
339 | void (*fl_notify)(struct file_lock *); /* unblock callback */ | |
b83be6f2 | 340 | int (*fl_grant)(struct file_lock *, struct file_lock *, int); |
1da177e4 LT |
341 | void (*fl_release_private)(struct file_lock *); |
342 | void (*fl_break)(struct file_lock *); /* break_lease callback */ | |
b83be6f2 CH |
343 | int (*fl_mylease)(struct file_lock *, struct file_lock *); |
344 | int (*fl_change)(struct file_lock **, int); | |
1da177e4 LT |
345 | |
346 | locking rules: | |
b83be6f2 CH |
347 | file_lock_lock may block |
348 | fl_compare_owner: yes no | |
349 | fl_notify: yes no | |
350 | fl_grant: no no | |
351 | fl_release_private: maybe no | |
352 | fl_break: yes no | |
353 | fl_mylease: yes no | |
354 | fl_change yes no | |
355 | ||
1da177e4 LT |
356 | --------------------------- buffer_head ----------------------------------- |
357 | prototypes: | |
358 | void (*b_end_io)(struct buffer_head *bh, int uptodate); | |
359 | ||
360 | locking rules: | |
361 | called from interrupts. In other words, extreme care is needed here. | |
362 | bh is locked, but that's all warranties we have here. Currently only RAID1, | |
363 | highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices | |
364 | call this method upon the IO completion. | |
365 | ||
366 | --------------------------- block_device_operations ----------------------- | |
367 | prototypes: | |
e1455d1b CH |
368 | int (*open) (struct block_device *, fmode_t); |
369 | int (*release) (struct gendisk *, fmode_t); | |
370 | int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long); | |
371 | int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long); | |
372 | int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *); | |
1da177e4 | 373 | int (*media_changed) (struct gendisk *); |
e1455d1b | 374 | void (*unlock_native_capacity) (struct gendisk *); |
1da177e4 | 375 | int (*revalidate_disk) (struct gendisk *); |
e1455d1b CH |
376 | int (*getgeo)(struct block_device *, struct hd_geometry *); |
377 | void (*swap_slot_free_notify) (struct block_device *, unsigned long); | |
1da177e4 LT |
378 | |
379 | locking rules: | |
b83be6f2 CH |
380 | bd_mutex |
381 | open: yes | |
382 | release: yes | |
383 | ioctl: no | |
384 | compat_ioctl: no | |
385 | direct_access: no | |
386 | media_changed: no | |
387 | unlock_native_capacity: no | |
388 | revalidate_disk: no | |
389 | getgeo: no | |
390 | swap_slot_free_notify: no (see below) | |
e1455d1b CH |
391 | |
392 | media_changed, unlock_native_capacity and revalidate_disk are called only from | |
393 | check_disk_change(). | |
394 | ||
395 | swap_slot_free_notify is called with swap_lock and sometimes the page lock | |
396 | held. | |
1da177e4 | 397 | |
1da177e4 LT |
398 | |
399 | --------------------------- file_operations ------------------------------- | |
400 | prototypes: | |
401 | loff_t (*llseek) (struct file *, loff_t, int); | |
402 | ssize_t (*read) (struct file *, char __user *, size_t, loff_t *); | |
1da177e4 | 403 | ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *); |
027445c3 BP |
404 | ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t); |
405 | ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t); | |
1da177e4 LT |
406 | int (*readdir) (struct file *, void *, filldir_t); |
407 | unsigned int (*poll) (struct file *, struct poll_table_struct *); | |
1da177e4 LT |
408 | long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); |
409 | long (*compat_ioctl) (struct file *, unsigned int, unsigned long); | |
410 | int (*mmap) (struct file *, struct vm_area_struct *); | |
411 | int (*open) (struct inode *, struct file *); | |
412 | int (*flush) (struct file *); | |
413 | int (*release) (struct inode *, struct file *); | |
7ea80859 | 414 | int (*fsync) (struct file *, int datasync); |
1da177e4 LT |
415 | int (*aio_fsync) (struct kiocb *, int datasync); |
416 | int (*fasync) (int, struct file *, int); | |
417 | int (*lock) (struct file *, int, struct file_lock *); | |
418 | ssize_t (*readv) (struct file *, const struct iovec *, unsigned long, | |
419 | loff_t *); | |
420 | ssize_t (*writev) (struct file *, const struct iovec *, unsigned long, | |
421 | loff_t *); | |
422 | ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, | |
423 | void __user *); | |
424 | ssize_t (*sendpage) (struct file *, struct page *, int, size_t, | |
425 | loff_t *, int); | |
426 | unsigned long (*get_unmapped_area)(struct file *, unsigned long, | |
427 | unsigned long, unsigned long, unsigned long); | |
428 | int (*check_flags)(int); | |
b83be6f2 CH |
429 | int (*flock) (struct file *, int, struct file_lock *); |
430 | ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, | |
431 | size_t, unsigned int); | |
432 | ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, | |
433 | size_t, unsigned int); | |
434 | int (*setlease)(struct file *, long, struct file_lock **); | |
1da177e4 LT |
435 | }; |
436 | ||
437 | locking rules: | |
b83be6f2 CH |
438 | All may block except for ->setlease. |
439 | No VFS locks held on entry except for ->fsync and ->setlease. | |
440 | ||
441 | ->fsync() has i_mutex on inode. | |
442 | ||
443 | ->setlease has the file_list_lock held and must not sleep. | |
1da177e4 LT |
444 | |
445 | ->llseek() locking has moved from llseek to the individual llseek | |
446 | implementations. If your fs is not using generic_file_llseek, you | |
447 | need to acquire and release the appropriate locks in your ->llseek(). | |
448 | For many filesystems, it is probably safe to acquire the inode | |
866707fc JB |
449 | mutex or just to use i_size_read() instead. |
450 | Note: this does not protect the file->f_pos against concurrent modifications | |
451 | since this is something the userspace has to take care about. | |
1da177e4 | 452 | |
b83be6f2 CH |
453 | ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags. |
454 | Most instances call fasync_helper(), which does that maintenance, so it's | |
455 | not normally something one needs to worry about. Return values > 0 will be | |
456 | mapped to zero in the VFS layer. | |
1da177e4 LT |
457 | |
458 | ->readdir() and ->ioctl() on directories must be changed. Ideally we would | |
459 | move ->readdir() to inode_operations and use a separate method for directory | |
460 | ->ioctl() or kill the latter completely. One of the problems is that for | |
461 | anything that resembles union-mount we won't have a struct file for all | |
462 | components. And there are other reasons why the current interface is a mess... | |
463 | ||
1da177e4 LT |
464 | ->read on directories probably must go away - we should just enforce -EISDIR |
465 | in sys_read() and friends. | |
466 | ||
1da177e4 LT |
467 | --------------------------- dquot_operations ------------------------------- |
468 | prototypes: | |
1da177e4 LT |
469 | int (*write_dquot) (struct dquot *); |
470 | int (*acquire_dquot) (struct dquot *); | |
471 | int (*release_dquot) (struct dquot *); | |
472 | int (*mark_dirty) (struct dquot *); | |
473 | int (*write_info) (struct super_block *, int); | |
474 | ||
475 | These operations are intended to be more or less wrapping functions that ensure | |
476 | a proper locking wrt the filesystem and call the generic quota operations. | |
477 | ||
478 | What filesystem should expect from the generic quota functions: | |
479 | ||
480 | FS recursion Held locks when called | |
1da177e4 LT |
481 | write_dquot: yes dqonoff_sem or dqptr_sem |
482 | acquire_dquot: yes dqonoff_sem or dqptr_sem | |
483 | release_dquot: yes dqonoff_sem or dqptr_sem | |
484 | mark_dirty: no - | |
485 | write_info: yes dqonoff_sem | |
486 | ||
487 | FS recursion means calling ->quota_read() and ->quota_write() from superblock | |
488 | operations. | |
489 | ||
1da177e4 LT |
490 | More details about quota locking can be found in fs/dquot.c. |
491 | ||
492 | --------------------------- vm_operations_struct ----------------------------- | |
493 | prototypes: | |
494 | void (*open)(struct vm_area_struct*); | |
495 | void (*close)(struct vm_area_struct*); | |
d0217ac0 | 496 | int (*fault)(struct vm_area_struct*, struct vm_fault *); |
c2ec175c | 497 | int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *); |
28b2ee20 | 498 | int (*access)(struct vm_area_struct *, unsigned long, void*, int, int); |
1da177e4 LT |
499 | |
500 | locking rules: | |
b83be6f2 CH |
501 | mmap_sem PageLocked(page) |
502 | open: yes | |
503 | close: yes | |
504 | fault: yes can return with page locked | |
505 | page_mkwrite: yes can return with page locked | |
506 | access: yes | |
ed2f2f9b | 507 | |
b827e496 NP |
508 | ->fault() is called when a previously not present pte is about |
509 | to be faulted in. The filesystem must find and return the page associated | |
510 | with the passed in "pgoff" in the vm_fault structure. If it is possible that | |
511 | the page may be truncated and/or invalidated, then the filesystem must lock | |
512 | the page, then ensure it is not already truncated (the page lock will block | |
513 | subsequent truncate), and then return with VM_FAULT_LOCKED, and the page | |
514 | locked. The VM will unlock the page. | |
515 | ||
516 | ->page_mkwrite() is called when a previously read-only pte is | |
517 | about to become writeable. The filesystem again must ensure that there are | |
518 | no truncate/invalidate races, and then return with the page locked. If | |
519 | the page has been truncated, the filesystem should not look up a new page | |
520 | like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which | |
521 | will cause the VM to retry the fault. | |
1da177e4 | 522 | |
28b2ee20 RR |
523 | ->access() is called when get_user_pages() fails in |
524 | acces_process_vm(), typically used to debug a process through | |
525 | /proc/pid/mem or ptrace. This function is needed only for | |
526 | VM_IO | VM_PFNMAP VMAs. | |
527 | ||
1da177e4 LT |
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) |