| blob | f5e3676db954b5bce4c23a0bf723a79d66181fcd |
1 =======
2 Locking
3 =======
5 The text below describes the locking rules for VFS-related methods.
6 It is (believed to be) up-to-date. *Please*, if you change anything in
7 prototypes or locking protocols - update this file. And update the relevant
8 instances in the tree, don't leave that to maintainers of filesystems/devices/
9 etc. At the very least, put the list of dubious cases in the end of this file.
10 Don't turn it into log - maintainers of out-of-the-tree code are supposed to
11 be able to use diff(1).
13 Thing currently missing here: socket operations. Alexey?
15 dentry_operations
16 =================
18 prototypes::
20 int (*d_revalidate)(struct dentry *, unsigned int);
21 int (*d_weak_revalidate)(struct dentry *, unsigned int);
22 int (*d_hash)(const struct dentry *, struct qstr *);
23 int (*d_compare)(const struct dentry *,
24 unsigned int, const char *, const struct qstr *);
25 int (*d_delete)(struct dentry *);
26 int (*d_init)(struct dentry *);
27 void (*d_release)(struct dentry *);
28 void (*d_iput)(struct dentry *, struct inode *);
29 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
30 struct vfsmount *(*d_automount)(struct path *path);
31 int (*d_manage)(const struct path *, bool);
32 struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
34 locking rules:
36 ================== =========== ======== ============== ========
37 ops rename_lock ->d_lock may block rcu-walk
38 ================== =========== ======== ============== ========
39 d_revalidate: no no yes (ref-walk) maybe
40 d_weak_revalidate: no no yes no
41 d_hash no no no maybe
42 d_compare: yes no no maybe
43 d_delete: no yes no no
44 d_init: no no yes no
45 d_release: no no yes no
46 d_prune: no yes no no
47 d_iput: no no yes no
48 d_dname: no no no no
49 d_automount: no no yes no
50 d_manage: no no yes (ref-walk) maybe
51 d_real no no yes no
52 ================== =========== ======== ============== ========
54 inode_operations
55 ================
57 prototypes::
59 int (*create) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t, bool);
60 struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
61 int (*link) (struct dentry *,struct inode *,struct dentry *);
62 int (*unlink) (struct inode *,struct dentry *);
63 int (*symlink) (struct mnt_idmap *, struct inode *,struct dentry *,const char *);
64 int (*mkdir) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t);
65 int (*rmdir) (struct inode *,struct dentry *);
66 int (*mknod) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t,dev_t);
67 int (*rename) (struct mnt_idmap *, struct inode *, struct dentry *,
68 struct inode *, struct dentry *, unsigned int);
69 int (*readlink) (struct dentry *, char __user *,int);
70 const char *(*get_link) (struct dentry *, struct inode *, struct delayed_call *);
71 void (*truncate) (struct inode *);
72 int (*permission) (struct mnt_idmap *, struct inode *, int, unsigned int);
73 struct posix_acl * (*get_inode_acl)(struct inode *, int, bool);
74 int (*setattr) (struct mnt_idmap *, struct dentry *, struct iattr *);
75 int (*getattr) (struct mnt_idmap *, const struct path *, struct kstat *, u32, unsigned int);
76 ssize_t (*listxattr) (struct dentry *, char *, size_t);
77 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
78 void (*update_time)(struct inode *, struct timespec *, int);
79 int (*atomic_open)(struct inode *, struct dentry *,
80 struct file *, unsigned open_flag,
81 umode_t create_mode);
82 int (*tmpfile) (struct mnt_idmap *, struct inode *,
83 struct file *, umode_t);
84 int (*fileattr_set)(struct mnt_idmap *idmap,
85 struct dentry *dentry, struct fileattr *fa);
86 int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
87 struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int);
88 struct offset_ctx *(*get_offset_ctx)(struct inode *inode);
90 locking rules:
91 all may block
93 ============== ==================================================
94 ops i_rwsem(inode)
95 ============== ==================================================
96 lookup: shared
97 create: exclusive
98 link: exclusive (both)
99 mknod: exclusive
100 symlink: exclusive
101 mkdir: exclusive
102 unlink: exclusive (both)
103 rmdir: exclusive (both)(see below)
104 rename: exclusive (both parents, some children) (see below)
105 readlink: no
106 get_link: no
107 setattr: exclusive
108 permission: no (may not block if called in rcu-walk mode)
109 get_inode_acl: no
110 get_acl: no
111 getattr: no
112 listxattr: no
113 fiemap: no
114 update_time: no
115 atomic_open: shared (exclusive if O_CREAT is set in open flags)
116 tmpfile: no
117 fileattr_get: no or exclusive
118 fileattr_set: exclusive
119 get_offset_ctx no
120 ============== ==================================================
123 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
124 exclusive on victim.
125 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
126 ->unlink() and ->rename() have ->i_rwsem exclusive on all non-directories
127 involved.
128 ->rename() has ->i_rwsem exclusive on any subdirectory that changes parent.
130 See Documentation/filesystems/directory-locking.rst for more detailed discussion
131 of the locking scheme for directory operations.
133 xattr_handler operations
134 ========================
136 prototypes::
138 bool (*list)(struct dentry *dentry);
139 int (*get)(const struct xattr_handler *handler, struct dentry *dentry,
140 struct inode *inode, const char *name, void *buffer,
141 size_t size);
142 int (*set)(const struct xattr_handler *handler,
143 struct mnt_idmap *idmap,
144 struct dentry *dentry, struct inode *inode, const char *name,
145 const void *buffer, size_t size, int flags);
147 locking rules:
148 all may block
150 ===== ==============
151 ops i_rwsem(inode)
152 ===== ==============
153 list: no
154 get: no
155 set: exclusive
156 ===== ==============
158 super_operations
159 ================
161 prototypes::
163 struct inode *(*alloc_inode)(struct super_block *sb);
164 void (*free_inode)(struct inode *);
165 void (*destroy_inode)(struct inode *);
166 void (*dirty_inode) (struct inode *, int flags);
167 int (*write_inode) (struct inode *, struct writeback_control *wbc);
168 int (*drop_inode) (struct inode *);
169 void (*evict_inode) (struct inode *);
170 void (*put_super) (struct super_block *);
171 int (*sync_fs)(struct super_block *sb, int wait);
172 int (*freeze_fs) (struct super_block *);
173 int (*unfreeze_fs) (struct super_block *);
174 int (*statfs) (struct dentry *, struct kstatfs *);
175 int (*remount_fs) (struct super_block *, int *, char *);
176 void (*umount_begin) (struct super_block *);
177 int (*show_options)(struct seq_file *, struct dentry *);
178 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
179 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
181 locking rules:
182 All may block [not true, see below]
184 ====================== ============ ========================
185 ops s_umount note
186 ====================== ============ ========================
187 alloc_inode:
188 free_inode: called from RCU callback
189 destroy_inode:
190 dirty_inode:
191 write_inode:
192 drop_inode: !!!inode->i_lock!!!
193 evict_inode:
194 put_super: write
195 sync_fs: read
196 freeze_fs: write
197 unfreeze_fs: write
198 statfs: maybe(read) (see below)
199 remount_fs: write
200 umount_begin: no
201 show_options: no (namespace_sem)
202 quota_read: no (see below)
203 quota_write: no (see below)
204 ====================== ============ ========================
206 ->statfs() has s_umount (shared) when called by ustat(2) (native or
207 compat), but that's an accident of bad API; s_umount is used to pin
208 the superblock down when we only have dev_t given us by userland to
209 identify the superblock. Everything else (statfs(), fstatfs(), etc.)
210 doesn't hold it when calling ->statfs() - superblock is pinned down
211 by resolving the pathname passed to syscall.
213 ->quota_read() and ->quota_write() functions are both guaranteed to
214 be the only ones operating on the quota file by the quota code (via
215 dqio_sem) (unless an admin really wants to screw up something and
216 writes to quota files with quotas on). For other details about locking
217 see also dquot_operations section.
219 file_system_type
220 ================
222 prototypes::
224 struct dentry *(*mount) (struct file_system_type *, int,
225 const char *, void *);
226 void (*kill_sb) (struct super_block *);
228 locking rules:
230 ======= =========
231 ops may block
232 ======= =========
233 mount yes
234 kill_sb yes
235 ======= =========
237 ->mount() returns ERR_PTR or the root dentry; its superblock should be locked
238 on return.
240 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
241 unlocks and drops the reference.
243 address_space_operations
244 ========================
245 prototypes::
247 int (*writepage)(struct page *page, struct writeback_control *wbc);
248 int (*read_folio)(struct file *, struct folio *);
249 int (*writepages)(struct address_space *, struct writeback_control *);
250 bool (*dirty_folio)(struct address_space *, struct folio *folio);
251 void (*readahead)(struct readahead_control *);
252 int (*write_begin)(struct file *, struct address_space *mapping,
253 loff_t pos, unsigned len,
254 struct folio **foliop, void **fsdata);
255 int (*write_end)(struct file *, struct address_space *mapping,
256 loff_t pos, unsigned len, unsigned copied,
257 struct folio *folio, void *fsdata);
258 sector_t (*bmap)(struct address_space *, sector_t);
259 void (*invalidate_folio) (struct folio *, size_t start, size_t len);
260 bool (*release_folio)(struct folio *, gfp_t);
261 void (*free_folio)(struct folio *);
262 int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
263 int (*migrate_folio)(struct address_space *, struct folio *dst,
264 struct folio *src, enum migrate_mode);
265 int (*launder_folio)(struct folio *);
266 bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count);
267 int (*error_remove_folio)(struct address_space *, struct folio *);
268 int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
269 int (*swap_deactivate)(struct file *);
270 int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
272 locking rules:
273 All except dirty_folio and free_folio may block
275 ====================== ======================== ========= ===============
276 ops folio locked i_rwsem invalidate_lock
277 ====================== ======================== ========= ===============
278 writepage: yes, unlocks (see below)
279 read_folio: yes, unlocks shared
280 writepages:
281 dirty_folio: maybe
282 readahead: yes, unlocks shared
283 write_begin: locks the folio exclusive
284 write_end: yes, unlocks exclusive
285 bmap:
286 invalidate_folio: yes exclusive
287 release_folio: yes
288 free_folio: yes
289 direct_IO:
290 migrate_folio: yes (both)
291 launder_folio: yes
292 is_partially_uptodate: yes
293 error_remove_folio: yes
294 swap_activate: no
295 swap_deactivate: no
296 swap_rw: yes, unlocks
297 ====================== ======================== ========= ===============
299 ->write_begin(), ->write_end() and ->read_folio() may be called from
300 the request handler (/dev/loop).
302 ->read_folio() unlocks the folio, either synchronously or via I/O
303 completion.
305 ->readahead() unlocks the folios that I/O is attempted on like ->read_folio().
307 ->writepage() is used for two purposes: for "memory cleansing" and for
308 "sync". These are quite different operations and the behaviour may differ
309 depending upon the mode.
311 If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
312 it *must* start I/O against the page, even if that would involve
313 blocking on in-progress I/O.
315 If writepage is called for memory cleansing (sync_mode ==
316 WBC_SYNC_NONE) then its role is to get as much writeout underway as
317 possible. So writepage should try to avoid blocking against
318 currently-in-progress I/O.
320 If the filesystem is not called for "sync" and it determines that it
321 would need to block against in-progress I/O to be able to start new I/O
322 against the page the filesystem should redirty the page with
323 redirty_page_for_writepage(), then unlock the page and return zero.
324 This may also be done to avoid internal deadlocks, but rarely.
326 If the filesystem is called for sync then it must wait on any
327 in-progress I/O and then start new I/O.
329 The filesystem should unlock the page synchronously, before returning to the
330 caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
331 value. WRITEPAGE_ACTIVATE means that page cannot really be written out
332 currently, and VM should stop calling ->writepage() on this page for some
333 time. VM does this by moving page to the head of the active list, hence the
334 name.
336 Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
337 and return zero, writepage *must* run set_page_writeback() against the page,
338 followed by unlocking it. Once set_page_writeback() has been run against the
339 page, write I/O can be submitted and the write I/O completion handler must run
340 end_page_writeback() once the I/O is complete. If no I/O is submitted, the
341 filesystem must run end_page_writeback() against the page before returning from
342 writepage.
344 That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
345 if the filesystem needs the page to be locked during writeout, that is ok, too,
346 the page is allowed to be unlocked at any point in time between the calls to
347 set_page_writeback() and end_page_writeback().
349 Note, failure to run either redirty_page_for_writepage() or the combination of
350 set_page_writeback()/end_page_writeback() on a page submitted to writepage
351 will leave the page itself marked clean but it will be tagged as dirty in the
352 radix tree. This incoherency can lead to all sorts of hard-to-debug problems
353 in the filesystem like having dirty inodes at umount and losing written data.
355 ->writepages() is used for periodic writeback and for syscall-initiated
356 sync operations. The address_space should start I/O against at least
357 ``*nr_to_write`` pages. ``*nr_to_write`` must be decremented for each page
358 which is written. The address_space implementation may write more (or less)
359 pages than ``*nr_to_write`` asks for, but it should try to be reasonably close.
360 If nr_to_write is NULL, all dirty pages must be written.
362 writepages should _only_ write pages which are present on
363 mapping->io_pages.
365 ->dirty_folio() is called from various places in the kernel when
366 the target folio is marked as needing writeback. The folio cannot be
367 truncated because either the caller holds the folio lock, or the caller
368 has found the folio while holding the page table lock which will block
369 truncation.
371 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
372 filesystems and by the swapper. The latter will eventually go away. Please,
373 keep it that way and don't breed new callers.
375 ->invalidate_folio() is called when the filesystem must attempt to drop
376 some or all of the buffers from the page when it is being truncated. It
377 returns zero on success. The filesystem must exclusively acquire
378 invalidate_lock before invalidating page cache in truncate / hole punch
379 path (and thus calling into ->invalidate_folio) to block races between page
380 cache invalidation and page cache filling functions (fault, read, ...).
382 ->release_folio() is called when the MM wants to make a change to the
383 folio that would invalidate the filesystem's private data. For example,
384 it may be about to be removed from the address_space or split. The folio
385 is locked and not under writeback. It may be dirty. The gfp parameter
386 is not usually used for allocation, but rather to indicate what the
387 filesystem may do to attempt to free the private data. The filesystem may
388 return false to indicate that the folio's private data cannot be freed.
389 If it returns true, it should have already removed the private data from
390 the folio. If a filesystem does not provide a ->release_folio method,
391 the pagecache will assume that private data is buffer_heads and call
392 try_to_free_buffers().
394 ->free_folio() is called when the kernel has dropped the folio
395 from the page cache.
397 ->launder_folio() may be called prior to releasing a folio if
398 it is still found to be dirty. It returns zero if the folio was successfully
399 cleaned, or an error value if not. Note that in order to prevent the folio
400 getting mapped back in and redirtied, it needs to be kept locked
401 across the entire operation.
403 ->swap_activate() will be called to prepare the given file for swap. It
404 should perform any validation and preparation necessary to ensure that
405 writes can be performed with minimal memory allocation. It should call
406 add_swap_extent(), or the helper iomap_swapfile_activate(), and return
407 the number of extents added. If IO should be submitted through
408 ->swap_rw(), it should set SWP_FS_OPS, otherwise IO will be submitted
409 directly to the block device ``sis->bdev``.
411 ->swap_deactivate() will be called in the sys_swapoff()
412 path after ->swap_activate() returned success.
414 ->swap_rw will be called for swap IO if SWP_FS_OPS was set by ->swap_activate().
416 file_lock_operations
417 ====================
419 prototypes::
421 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
422 void (*fl_release_private)(struct file_lock *);
425 locking rules:
427 =================== ============= =========
428 ops inode->i_lock may block
429 =================== ============= =========
430 fl_copy_lock: yes no
431 fl_release_private: maybe maybe[1]_
432 =================== ============= =========
434 .. [1]:
435 ->fl_release_private for flock or POSIX locks is currently allowed
436 to block. Leases however can still be freed while the i_lock is held and
437 so fl_release_private called on a lease should not block.
439 lock_manager_operations
440 =======================
442 prototypes::
444 void (*lm_notify)(struct file_lock *); /* unblock callback */
445 int (*lm_grant)(struct file_lock *, struct file_lock *, int);
446 void (*lm_break)(struct file_lock *); /* break_lease callback */
447 int (*lm_change)(struct file_lock **, int);
448 bool (*lm_breaker_owns_lease)(struct file_lock *);
449 bool (*lm_lock_expirable)(struct file_lock *);
450 void (*lm_expire_lock)(void);
452 locking rules:
454 ====================== ============= ================= =========
455 ops flc_lock blocked_lock_lock may block
456 ====================== ============= ================= =========
457 lm_notify: no yes no
458 lm_grant: no no no
459 lm_break: yes no no
460 lm_change yes no no
461 lm_breaker_owns_lease: yes no no
462 lm_lock_expirable yes no no
463 lm_expire_lock no no yes
464 ====================== ============= ================= =========
466 buffer_head
467 ===========
469 prototypes::
471 void (*b_end_io)(struct buffer_head *bh, int uptodate);
473 locking rules:
475 called from interrupts. In other words, extreme care is needed here.
476 bh is locked, but that's all warranties we have here. Currently only RAID1,
477 highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
478 call this method upon the IO completion.
480 block_device_operations
481 =======================
482 prototypes::
484 int (*open) (struct block_device *, fmode_t);
485 int (*release) (struct gendisk *, fmode_t);
486 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
487 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
488 int (*direct_access) (struct block_device *, sector_t, void **,
489 unsigned long *);
490 void (*unlock_native_capacity) (struct gendisk *);
491 int (*getgeo)(struct block_device *, struct hd_geometry *);
492 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
494 locking rules:
496 ======================= ===================
497 ops open_mutex
498 ======================= ===================
499 open: yes
500 release: yes
501 ioctl: no
502 compat_ioctl: no
503 direct_access: no
504 unlock_native_capacity: no
505 getgeo: no
506 swap_slot_free_notify: no (see below)
507 ======================= ===================
509 swap_slot_free_notify is called with swap_lock and sometimes the page lock
510 held.
513 file_operations
514 ===============
516 prototypes::
518 loff_t (*llseek) (struct file *, loff_t, int);
519 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
520 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
521 ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
522 ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
523 int (*iopoll) (struct kiocb *kiocb, bool spin);
524 int (*iterate_shared) (struct file *, struct dir_context *);
525 __poll_t (*poll) (struct file *, struct poll_table_struct *);
526 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
527 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
528 int (*mmap) (struct file *, struct vm_area_struct *);
529 int (*open) (struct inode *, struct file *);
530 int (*flush) (struct file *);
531 int (*release) (struct inode *, struct file *);
532 int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
533 int (*fasync) (int, struct file *, int);
534 int (*lock) (struct file *, int, struct file_lock *);
535 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
536 unsigned long, unsigned long, unsigned long);
537 int (*check_flags)(int);
538 int (*flock) (struct file *, int, struct file_lock *);
539 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
540 size_t, unsigned int);
541 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
542 size_t, unsigned int);
543 int (*setlease)(struct file *, long, struct file_lock **, void **);
544 long (*fallocate)(struct file *, int, loff_t, loff_t);
545 void (*show_fdinfo)(struct seq_file *m, struct file *f);
546 unsigned (*mmap_capabilities)(struct file *);
547 ssize_t (*copy_file_range)(struct file *, loff_t, struct file *,
548 loff_t, size_t, unsigned int);
549 loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in,
550 struct file *file_out, loff_t pos_out,
551 loff_t len, unsigned int remap_flags);
552 int (*fadvise)(struct file *, loff_t, loff_t, int);
554 locking rules:
555 All may block.
557 ->llseek() locking has moved from llseek to the individual llseek
558 implementations. If your fs is not using generic_file_llseek, you
559 need to acquire and release the appropriate locks in your ->llseek().
560 For many filesystems, it is probably safe to acquire the inode
561 mutex or just to use i_size_read() instead.
562 Note: this does not protect the file->f_pos against concurrent modifications
563 since this is something the userspace has to take care about.
565 ->iterate_shared() is called with i_rwsem held for reading, and with the
566 file f_pos_lock held exclusively
568 ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
569 Most instances call fasync_helper(), which does that maintenance, so it's
570 not normally something one needs to worry about. Return values > 0 will be
571 mapped to zero in the VFS layer.
573 ->readdir() and ->ioctl() on directories must be changed. Ideally we would
574 move ->readdir() to inode_operations and use a separate method for directory
575 ->ioctl() or kill the latter completely. One of the problems is that for
576 anything that resembles union-mount we won't have a struct file for all
577 components. And there are other reasons why the current interface is a mess...
579 ->read on directories probably must go away - we should just enforce -EISDIR
580 in sys_read() and friends.
582 ->setlease operations should call generic_setlease() before or after setting
583 the lease within the individual filesystem to record the result of the
584 operation
586 ->fallocate implementation must be really careful to maintain page cache
587 consistency when punching holes or performing other operations that invalidate
588 page cache contents. Usually the filesystem needs to call
589 truncate_inode_pages_range() to invalidate relevant range of the page cache.
590 However the filesystem usually also needs to update its internal (and on disk)
591 view of file offset -> disk block mapping. Until this update is finished, the
592 filesystem needs to block page faults and reads from reloading now-stale page
593 cache contents from the disk. Since VFS acquires mapping->invalidate_lock in
594 shared mode when loading pages from disk (filemap_fault(), filemap_read(),
595 readahead paths), the fallocate implementation must take the invalidate_lock to
596 prevent reloading.
598 ->copy_file_range and ->remap_file_range implementations need to serialize
599 against modifications of file data while the operation is running. For
600 blocking changes through write(2) and similar operations inode->i_rwsem can be
601 used. To block changes to file contents via a memory mapping during the
602 operation, the filesystem must take mapping->invalidate_lock to coordinate
603 with ->page_mkwrite.
605 dquot_operations
606 ================
608 prototypes::
610 int (*write_dquot) (struct dquot *);
611 int (*acquire_dquot) (struct dquot *);
612 int (*release_dquot) (struct dquot *);
613 int (*mark_dirty) (struct dquot *);
614 int (*write_info) (struct super_block *, int);
616 These operations are intended to be more or less wrapping functions that ensure
617 a proper locking wrt the filesystem and call the generic quota operations.
619 What filesystem should expect from the generic quota functions:
621 ============== ============ =========================
622 ops FS recursion Held locks when called
623 ============== ============ =========================
624 write_dquot: yes dqonoff_sem or dqptr_sem
625 acquire_dquot: yes dqonoff_sem or dqptr_sem
626 release_dquot: yes dqonoff_sem or dqptr_sem
627 mark_dirty: no -
628 write_info: yes dqonoff_sem
629 ============== ============ =========================
631 FS recursion means calling ->quota_read() and ->quota_write() from superblock
632 operations.
634 More details about quota locking can be found in fs/dquot.c.
636 vm_operations_struct
637 ====================
639 prototypes::
641 void (*open)(struct vm_area_struct *);
642 void (*close)(struct vm_area_struct *);
643 vm_fault_t (*fault)(struct vm_fault *);
644 vm_fault_t (*huge_fault)(struct vm_fault *, unsigned int order);
645 vm_fault_t (*map_pages)(struct vm_fault *, pgoff_t start, pgoff_t end);
646 vm_fault_t (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
647 vm_fault_t (*pfn_mkwrite)(struct vm_area_struct *, struct vm_fault *);
648 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
650 locking rules:
652 ============= ========== ===========================
653 ops mmap_lock PageLocked(page)
654 ============= ========== ===========================
655 open: write
656 close: read/write
657 fault: read can return with page locked
658 huge_fault: maybe-read
659 map_pages: maybe-read
660 page_mkwrite: read can return with page locked
661 pfn_mkwrite: read
662 access: read
663 ============= ========== ===========================
665 ->fault() is called when a previously not present pte is about to be faulted
666 in. The filesystem must find and return the page associated with the passed in
667 "pgoff" in the vm_fault structure. If it is possible that the page may be
668 truncated and/or invalidated, then the filesystem must lock invalidate_lock,
669 then ensure the page is not already truncated (invalidate_lock will block
670 subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
671 locked. The VM will unlock the page.
673 ->huge_fault() is called when there is no PUD or PMD entry present. This
674 gives the filesystem the opportunity to install a PUD or PMD sized page.
675 Filesystems can also use the ->fault method to return a PMD sized page,
676 so implementing this function may not be necessary. In particular,
677 filesystems should not call filemap_fault() from ->huge_fault().
678 The mmap_lock may not be held when this method is called.
680 ->map_pages() is called when VM asks to map easy accessible pages.
681 Filesystem should find and map pages associated with offsets from "start_pgoff"
682 till "end_pgoff". ->map_pages() is called with the RCU lock held and must
683 not block. If it's not possible to reach a page without blocking,
684 filesystem should skip it. Filesystem should use set_pte_range() to setup
685 page table entry. Pointer to entry associated with the page is passed in
686 "pte" field in vm_fault structure. Pointers to entries for other offsets
687 should be calculated relative to "pte".
689 ->page_mkwrite() is called when a previously read-only pte is about to become
690 writeable. The filesystem again must ensure that there are no
691 truncate/invalidate races or races with operations such as ->remap_file_range
692 or ->copy_file_range, and then return with the page locked. Usually
693 mapping->invalidate_lock is suitable for proper serialization. If the page has
694 been truncated, the filesystem should not look up a new page like the ->fault()
695 handler, but simply return with VM_FAULT_NOPAGE, which will cause the VM to
696 retry the fault.
698 ->pfn_mkwrite() is the same as page_mkwrite but when the pte is
699 VM_PFNMAP or VM_MIXEDMAP with a page-less entry. Expected return is
700 VM_FAULT_NOPAGE. Or one of the VM_FAULT_ERROR types. The default behavior
701 after this call is to make the pte read-write, unless pfn_mkwrite returns
702 an error.
704 ->access() is called when get_user_pages() fails in
705 access_process_vm(), typically used to debug a process through
706 /proc/pid/mem or ptrace. This function is needed only for
707 VM_IO | VM_PFNMAP VMAs.
709 --------------------------------------------------------------------------------
711 Dubious stuff
713 (if you break something or notice that it is broken and do not fix it yourself
714 - at least put it here)