blob: 96d4293607ecfe22ed30e8d0ab518a8ddacbbba9 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001 The text below describes the locking rules for VFS-related methods.
2It is (believed to be) up-to-date. *Please*, if you change anything in
3prototypes or locking protocols - update this file. And update the relevant
4instances in the tree, don't leave that to maintainers of filesystems/devices/
5etc. At the very least, put the list of dubious cases in the end of this file.
6Don't turn it into log - maintainers of out-of-the-tree code are supposed to
7be able to use diff(1).
8 Thing currently missing here: socket operations. Alexey?
9
10--------------------------- dentry_operations --------------------------
11prototypes:
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 *);
Eric Dumazetc23fbb62007-05-08 00:26:18 -070018 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
Linus Torvalds1da177e2005-04-16 15:20:36 -070019
20locking rules:
21 none have BKL
22 dcache_lock rename_lock ->d_lock may block
23d_revalidate: no no no yes
24d_hash no no no yes
25d_compare: no yes no no
26d_delete: yes no yes no
27d_release: no no no yes
28d_iput: no no no yes
Eric Dumazetc23fbb62007-05-08 00:26:18 -070029d_dname: no no no no
Linus Torvalds1da177e2005-04-16 15:20:36 -070030
31--------------------------- inode_operations ---------------------------
32prototypes:
33 int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
34 struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
35ata *);
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
55locking rules:
56 all may block, none have BKL
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020057 i_mutex(inode)
Linus Torvalds1da177e2005-04-16 15:20:36 -070058lookup: yes
59create: yes
60link: yes (both)
61mknod: yes
62symlink: yes
63mkdir: yes
64unlink: yes (both)
65rmdir: yes (both) (see below)
66rename: yes (all) (see below)
67readlink: no
68follow_link: no
69truncate: yes (see below)
70setattr: yes
71permission: no
72getattr: no
73setxattr: yes
74getxattr: no
75listxattr: no
76removexattr: yes
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020077 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
Linus Torvalds1da177e2005-04-16 15:20:36 -070078victim.
79 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
80 ->truncate() is never called directly - it's a callback, not a
81method. It's called by vmtruncate() - library function normally used by
82->setattr(). Locking information above applies to that call (i.e. is
83inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
84passed).
85
86See Documentation/filesystems/directory-locking for more detailed discussion
87of the locking scheme for directory operations.
88
89--------------------------- super_operations ---------------------------
90prototypes:
91 struct inode *(*alloc_inode)(struct super_block *sb);
92 void (*destroy_inode)(struct inode *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070093 void (*dirty_inode) (struct inode *);
94 int (*write_inode) (struct inode *, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070095 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);
Takashi Satoc4be0c12009-01-09 16:40:58 -0800100 int (*freeze_fs) (struct super_block *);
101 int (*unfreeze_fs) (struct super_block *);
David Howells726c3342006-06-23 02:02:58 -0700102 int (*statfs) (struct dentry *, struct kstatfs *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103 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
110locking rules:
111 All may block.
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200112 None have BKL
113 s_umount
114alloc_inode:
115destroy_inode:
116dirty_inode: (must not sleep)
117write_inode:
118drop_inode: !!!inode_lock!!!
119delete_inode:
120put_super: write
121write_super: read
122sync_fs: read
123freeze_fs: read
124unfreeze_fs: read
125statfs: no
126remount_fs: maybe (see below)
127clear_inode:
128umount_begin: no
129show_options: no (namespace_sem)
130quota_read: no (see below)
131quota_write: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200133->remount_fs() will have the s_umount exclusive lock if it's already mounted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700134When called from get_sb_single, it does NOT have the s_umount lock.
135->quota_read() and ->quota_write() functions are both guaranteed to
136be the only ones operating on the quota file by the quota code (via
137dqio_sem) (unless an admin really wants to screw up something and
138writes to quota files with quotas on). For other details about locking
139see also dquot_operations section.
140
141--------------------------- file_system_type ---------------------------
142prototypes:
Jonathan Corbet5d8b2eb2006-07-10 04:44:07 -0700143 int (*get_sb) (struct file_system_type *, int,
144 const char *, void *, struct vfsmount *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145 void (*kill_sb) (struct super_block *);
146locking rules:
147 may block BKL
Christoph Hellwigadaae722008-09-09 20:02:01 +0200148get_sb yes no
149kill_sb yes no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150
David Howells454e2392006-06-23 02:02:57 -0700151->get_sb() returns error or 0 with locked superblock attached to the vfsmount
152(exclusive on ->s_umount).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153->kill_sb() takes a write-locked superblock, does all shutdown work on it,
154unlocks and drops the reference.
155
156--------------------------- address_space_operations --------------------------
157prototypes:
158 int (*writepage)(struct page *page, struct writeback_control *wbc);
159 int (*readpage)(struct file *, struct page *);
160 int (*sync_page)(struct page *);
161 int (*writepages)(struct address_space *, struct writeback_control *);
162 int (*set_page_dirty)(struct page *page);
163 int (*readpages)(struct file *filp, struct address_space *mapping,
164 struct list_head *pages, unsigned nr_pages);
Nick Piggin4e02ed42008-10-29 14:00:55 -0700165 int (*write_begin)(struct file *, struct address_space *mapping,
166 loff_t pos, unsigned len, unsigned flags,
167 struct page **pagep, void **fsdata);
168 int (*write_end)(struct file *, struct address_space *mapping,
169 loff_t pos, unsigned len, unsigned copied,
170 struct page *page, void *fsdata);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171 sector_t (*bmap)(struct address_space *, sector_t);
172 int (*invalidatepage) (struct page *, unsigned long);
173 int (*releasepage) (struct page *, int);
174 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
175 loff_t offset, unsigned long nr_segs);
Trond Myklebuste3db7692007-01-10 23:15:39 -0800176 int (*launder_page) (struct page *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177
178locking rules:
179 All except set_page_dirty may block
180
Thadeu Lima de Souza Cascardoca0dbd82010-05-07 16:52:26 -0300181 BKL PageLocked(page) i_mutex
Linus Torvalds1da177e2005-04-16 15:20:36 -0700182writepage: no yes, unlocks (see below)
183readpage: no yes, unlocks
184sync_page: no maybe
185writepages: no
186set_page_dirty no no
187readpages: no
Nick Pigginafddba42007-10-16 01:25:01 -0700188write_begin: no locks the page yes
189write_end: no yes, unlocks yes
190perform_write: no n/a yes
Al Virofe36adf2009-06-16 13:35:01 -0400191bmap: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192invalidatepage: no yes
193releasepage: no yes
194direct_IO: no
Trond Myklebuste3db7692007-01-10 23:15:39 -0800195launder_page: no yes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700196
Nick Piggin4e02ed42008-10-29 14:00:55 -0700197 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700198may be called from the request handler (/dev/loop).
199
200 ->readpage() unlocks the page, either synchronously or via I/O
201completion.
202
203 ->readpages() populates the pagecache with the passed pages and starts
204I/O against them. They come unlocked upon I/O completion.
205
206 ->writepage() is used for two purposes: for "memory cleansing" and for
207"sync". These are quite different operations and the behaviour may differ
208depending upon the mode.
209
210If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
211it *must* start I/O against the page, even if that would involve
212blocking on in-progress I/O.
213
214If writepage is called for memory cleansing (sync_mode ==
215WBC_SYNC_NONE) then its role is to get as much writeout underway as
216possible. So writepage should try to avoid blocking against
217currently-in-progress I/O.
218
219If the filesystem is not called for "sync" and it determines that it
220would need to block against in-progress I/O to be able to start new I/O
221against the page the filesystem should redirty the page with
222redirty_page_for_writepage(), then unlock the page and return zero.
223This may also be done to avoid internal deadlocks, but rarely.
224
Robert P. J. Day3a4fa0a2007-10-19 23:10:43 +0200225If the filesystem is called for sync then it must wait on any
Linus Torvalds1da177e2005-04-16 15:20:36 -0700226in-progress I/O and then start new I/O.
227
Nikita Danilov20546062005-05-01 08:58:37 -0700228The filesystem should unlock the page synchronously, before returning to the
229caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
230value. WRITEPAGE_ACTIVATE means that page cannot really be written out
231currently, and VM should stop calling ->writepage() on this page for some
232time. VM does this by moving page to the head of the active list, hence the
233name.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700234
235Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
236and return zero, writepage *must* run set_page_writeback() against the page,
237followed by unlocking it. Once set_page_writeback() has been run against the
238page, write I/O can be submitted and the write I/O completion handler must run
239end_page_writeback() once the I/O is complete. If no I/O is submitted, the
240filesystem must run end_page_writeback() against the page before returning from
241writepage.
242
243That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
244if the filesystem needs the page to be locked during writeout, that is ok, too,
245the page is allowed to be unlocked at any point in time between the calls to
246set_page_writeback() and end_page_writeback().
247
248Note, failure to run either redirty_page_for_writepage() or the combination of
249set_page_writeback()/end_page_writeback() on a page submitted to writepage
250will leave the page itself marked clean but it will be tagged as dirty in the
251radix tree. This incoherency can lead to all sorts of hard-to-debug problems
252in the filesystem like having dirty inodes at umount and losing written data.
253
254 ->sync_page() locking rules are not well-defined - usually it is called
255with lock on page, but that is not guaranteed. Considering the currently
256existing instances of this method ->sync_page() itself doesn't look
257well-defined...
258
259 ->writepages() is used for periodic writeback and for syscall-initiated
260sync operations. The address_space should start I/O against at least
261*nr_to_write pages. *nr_to_write must be decremented for each page which is
262written. The address_space implementation may write more (or less) pages
263than *nr_to_write asks for, but it should try to be reasonably close. If
264nr_to_write is NULL, all dirty pages must be written.
265
266writepages should _only_ write pages which are present on
267mapping->io_pages.
268
269 ->set_page_dirty() is called from various places in the kernel
270when the target page is marked as needing writeback. It may be called
271under spinlock (it cannot block) and is sometimes called with the page
272not locked.
273
274 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
275filesystems and by the swapper. The latter will eventually go away. All
276instances do not actually need the BKL. Please, keep it that way and don't
277breed new callers.
278
279 ->invalidatepage() is called when the filesystem must attempt to drop
280some or all of the buffers from the page when it is being truncated. It
281returns zero on success. If ->invalidatepage is zero, the kernel uses
282block_invalidatepage() instead.
283
284 ->releasepage() is called when the kernel is about to try to drop the
285buffers from the page in preparation for freeing it. It returns zero to
286indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
287the kernel assumes that the fs has no private interest in the buffers.
288
Trond Myklebuste3db7692007-01-10 23:15:39 -0800289 ->launder_page() may be called prior to releasing a page if
290it is still found to be dirty. It returns zero if the page was successfully
291cleaned, or an error value if not. Note that in order to prevent the page
292getting mapped back in and redirtied, it needs to be kept locked
293across the entire operation.
294
Linus Torvalds1da177e2005-04-16 15:20:36 -0700295 Note: currently almost all instances of address_space methods are
296using BKL for internal serialization and that's one of the worst sources
297of contention. Normally they are calling library functions (in fs/buffer.c)
298and pass foo_get_block() as a callback (on local block-based filesystems,
299indeed). BKL is not needed for library stuff and is usually taken by
300foo_get_block(). It's an overkill, since block bitmaps can be protected by
301internal fs locking and real critical areas are much smaller than the areas
302filesystems protect now.
303
304----------------------- file_lock_operations ------------------------------
305prototypes:
306 void (*fl_insert)(struct file_lock *); /* lock insertion callback */
307 void (*fl_remove)(struct file_lock *); /* lock removal callback */
308 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
309 void (*fl_release_private)(struct file_lock *);
310
311
312locking rules:
313 BKL may block
314fl_insert: yes no
315fl_remove: yes no
316fl_copy_lock: yes no
317fl_release_private: yes yes
318
319----------------------- lock_manager_operations ---------------------------
320prototypes:
321 int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
322 void (*fl_notify)(struct file_lock *); /* unblock callback */
323 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
324 void (*fl_release_private)(struct file_lock *);
325 void (*fl_break)(struct file_lock *); /* break_lease callback */
326
327locking rules:
328 BKL may block
329fl_compare_owner: yes no
330fl_notify: yes no
331fl_copy_lock: yes no
332fl_release_private: yes yes
333fl_break: yes no
334
335 Currently only NFSD and NLM provide instances of this class. None of the
336them block. If you have out-of-tree instances - please, show up. Locking
337in that area will change.
338--------------------------- buffer_head -----------------------------------
339prototypes:
340 void (*b_end_io)(struct buffer_head *bh, int uptodate);
341
342locking rules:
343 called from interrupts. In other words, extreme care is needed here.
344bh is locked, but that's all warranties we have here. Currently only RAID1,
345highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
346call this method upon the IO completion.
347
348--------------------------- block_device_operations -----------------------
349prototypes:
350 int (*open) (struct inode *, struct file *);
351 int (*release) (struct inode *, struct file *);
352 int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long);
353 int (*media_changed) (struct gendisk *);
354 int (*revalidate_disk) (struct gendisk *);
355
356locking rules:
357 BKL bd_sem
358open: yes yes
359release: yes yes
360ioctl: yes no
361media_changed: no no
362revalidate_disk: no no
363
364The last two are called only from check_disk_change().
365
366--------------------------- file_operations -------------------------------
367prototypes:
368 loff_t (*llseek) (struct file *, loff_t, int);
369 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700370 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
Badari Pulavarty027445c2006-09-30 23:28:46 -0700371 ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
372 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700373 int (*readdir) (struct file *, void *, filldir_t);
374 unsigned int (*poll) (struct file *, struct poll_table_struct *);
375 int (*ioctl) (struct inode *, struct file *, unsigned int,
376 unsigned long);
377 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
378 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
379 int (*mmap) (struct file *, struct vm_area_struct *);
380 int (*open) (struct inode *, struct file *);
381 int (*flush) (struct file *);
382 int (*release) (struct inode *, struct file *);
Christoph Hellwig7ea80852010-05-26 17:53:25 +0200383 int (*fsync) (struct file *, int datasync);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700384 int (*aio_fsync) (struct kiocb *, int datasync);
385 int (*fasync) (int, struct file *, int);
386 int (*lock) (struct file *, int, struct file_lock *);
387 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
388 loff_t *);
389 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
390 loff_t *);
391 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
392 void __user *);
393 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
394 loff_t *, int);
395 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
396 unsigned long, unsigned long, unsigned long);
397 int (*check_flags)(int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700398};
399
400locking rules:
Tejun Heo5f820f62009-01-06 14:40:59 -0800401 All may block.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700402 BKL
403llseek: no (see below)
404read: no
405aio_read: no
406write: no
407aio_write: no
408readdir: no
409poll: no
410ioctl: yes (see below)
411unlocked_ioctl: no (see below)
412compat_ioctl: no
413mmap: no
Christoph Hellwigadaae722008-09-09 20:02:01 +0200414open: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700415flush: no
416release: no
417fsync: no (see below)
418aio_fsync: no
Christoph Hellwigadaae722008-09-09 20:02:01 +0200419fasync: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700420lock: yes
421readv: no
422writev: no
423sendfile: no
424sendpage: no
425get_unmapped_area: no
426check_flags: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700427
428->llseek() locking has moved from llseek to the individual llseek
429implementations. If your fs is not using generic_file_llseek, you
430need to acquire and release the appropriate locks in your ->llseek().
431For many filesystems, it is probably safe to acquire the inode
Jan Blunck866707f2010-05-26 14:44:54 -0700432mutex or just to use i_size_read() instead.
433Note: this does not protect the file->f_pos against concurrent modifications
434since this is something the userspace has to take care about.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700435
Linus Torvalds1da177e2005-04-16 15:20:36 -0700436Note: ext2_release() was *the* source of contention on fs-intensive
437loads and dropping BKL on ->release() helps to get rid of that (we still
438grab BKL for cases when we close a file that had been opened r/w, but that
439can and should be done using the internal locking with smaller critical areas).
440Current worst offender is ext2_get_block()...
441
Jonathan Corbet76398422009-02-01 14:26:59 -0700442->fasync() is called without BKL protection, and is responsible for
443maintaining the FASYNC bit in filp->f_flags. Most instances call
444fasync_helper(), which does that maintenance, so it's not normally
445something one needs to worry about. Return values > 0 will be mapped to
446zero in the VFS layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700447
448->readdir() and ->ioctl() on directories must be changed. Ideally we would
449move ->readdir() to inode_operations and use a separate method for directory
450->ioctl() or kill the latter completely. One of the problems is that for
451anything that resembles union-mount we won't have a struct file for all
452components. And there are other reasons why the current interface is a mess...
453
454->ioctl() on regular files is superceded by the ->unlocked_ioctl() that
455doesn't take the BKL.
456
457->read on directories probably must go away - we should just enforce -EISDIR
458in sys_read() and friends.
459
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +0200460->fsync() has i_mutex on inode.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700461
462--------------------------- dquot_operations -------------------------------
463prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700464 int (*write_dquot) (struct dquot *);
465 int (*acquire_dquot) (struct dquot *);
466 int (*release_dquot) (struct dquot *);
467 int (*mark_dirty) (struct dquot *);
468 int (*write_info) (struct super_block *, int);
469
470These operations are intended to be more or less wrapping functions that ensure
471a proper locking wrt the filesystem and call the generic quota operations.
472
473What filesystem should expect from the generic quota functions:
474
475 FS recursion Held locks when called
Linus Torvalds1da177e2005-04-16 15:20:36 -0700476write_dquot: yes dqonoff_sem or dqptr_sem
477acquire_dquot: yes dqonoff_sem or dqptr_sem
478release_dquot: yes dqonoff_sem or dqptr_sem
479mark_dirty: no -
480write_info: yes dqonoff_sem
481
482FS recursion means calling ->quota_read() and ->quota_write() from superblock
483operations.
484
Linus Torvalds1da177e2005-04-16 15:20:36 -0700485More details about quota locking can be found in fs/dquot.c.
486
487--------------------------- vm_operations_struct -----------------------------
488prototypes:
489 void (*open)(struct vm_area_struct*);
490 void (*close)(struct vm_area_struct*);
Nick Piggind0217ac2007-07-19 01:47:03 -0700491 int (*fault)(struct vm_area_struct*, struct vm_fault *);
Nick Pigginc2ec1752009-03-31 15:23:21 -0700492 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
Rik van Riel28b2ee22008-07-23 21:27:05 -0700493 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700494
495locking rules:
Mark Fashehed2f2f92007-07-19 01:47:01 -0700496 BKL mmap_sem PageLocked(page)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700497open: no yes
498close: no yes
Nick Pigginb827e492009-04-30 15:08:16 -0700499fault: no yes can return with page locked
500page_mkwrite: no yes can return with page locked
Rik van Riel28b2ee22008-07-23 21:27:05 -0700501access: no yes
Mark Fashehed2f2f92007-07-19 01:47:01 -0700502
Nick Pigginb827e492009-04-30 15:08:16 -0700503 ->fault() is called when a previously not present pte is about
504to be faulted in. The filesystem must find and return the page associated
505with the passed in "pgoff" in the vm_fault structure. If it is possible that
506the page may be truncated and/or invalidated, then the filesystem must lock
507the page, then ensure it is not already truncated (the page lock will block
508subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
509locked. The VM will unlock the page.
510
511 ->page_mkwrite() is called when a previously read-only pte is
512about to become writeable. The filesystem again must ensure that there are
513no truncate/invalidate races, and then return with the page locked. If
514the page has been truncated, the filesystem should not look up a new page
515like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
516will cause the VM to retry the fault.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700517
Rik van Riel28b2ee22008-07-23 21:27:05 -0700518 ->access() is called when get_user_pages() fails in
519acces_process_vm(), typically used to debug a process through
520/proc/pid/mem or ptrace. This function is needed only for
521VM_IO | VM_PFNMAP VMAs.
522
Linus Torvalds1da177e2005-04-16 15:20:36 -0700523================================================================================
524 Dubious stuff
525
526(if you break something or notice that it is broken and do not fix it yourself
527- at least put it here)
528
529ipc/shm.c::shm_delete() - may need BKL.
530->read() and ->write() in many drivers are (probably) missing BKL.