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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:
Al Viro0b728e12012-06-10 16:03:43 -040012 int (*d_revalidate)(struct dentry *, unsigned int);
Jeff Laytonecf3d1f2013-02-20 11:19:05 -050013 int (*d_weak_revalidate)(struct dentry *, unsigned int);
Linus Torvaldsda53be12013-05-21 15:22:44 -070014 int (*d_hash)(const struct dentry *, struct qstr *);
15 int (*d_compare)(const struct dentry *, const struct dentry *,
Nick Piggin621e1552011-01-07 17:49:27 +110016 unsigned int, const char *, const struct qstr *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070017 int (*d_delete)(struct dentry *);
18 void (*d_release)(struct dentry *);
19 void (*d_iput)(struct dentry *, struct inode *);
Eric Dumazetc23fbb62007-05-08 00:26:18 -070020 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
David Howells9875cf82011-01-14 18:45:21 +000021 struct vfsmount *(*d_automount)(struct path *path);
David Howellscc53ce52011-01-14 18:45:26 +000022 int (*d_manage)(struct dentry *, bool);
Linus Torvalds1da177e2005-04-16 15:20:36 -070023
24locking rules:
Nick Piggin34286d62011-01-07 17:49:57 +110025 rename_lock ->d_lock may block rcu-walk
26d_revalidate: no no yes (ref-walk) maybe
Jeff Laytonecf3d1f2013-02-20 11:19:05 -050027d_weak_revalidate:no no yes no
Nick Piggin34286d62011-01-07 17:49:57 +110028d_hash no no no maybe
29d_compare: yes no no maybe
30d_delete: no yes no no
31d_release: no no yes no
Sage Weilf0023bc2011-10-28 10:02:42 -070032d_prune: no yes no no
Nick Piggin34286d62011-01-07 17:49:57 +110033d_iput: no no yes no
34d_dname: no no no no
David Howells9875cf82011-01-14 18:45:21 +000035d_automount: no no yes no
David Howellsab909112011-01-14 18:46:51 +000036d_manage: no no yes (ref-walk) maybe
Linus Torvalds1da177e2005-04-16 15:20:36 -070037
38--------------------------- inode_operations ---------------------------
39prototypes:
Al Viroebfc3b42012-06-10 18:05:36 -040040 int (*create) (struct inode *,struct dentry *,umode_t, bool);
Al Viro00cd8dd2012-06-10 17:13:09 -040041 struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070042 int (*link) (struct dentry *,struct inode *,struct dentry *);
43 int (*unlink) (struct inode *,struct dentry *);
44 int (*symlink) (struct inode *,struct dentry *,const char *);
Al Viro18bb1db2011-07-26 01:41:39 -040045 int (*mkdir) (struct inode *,struct dentry *,umode_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -070046 int (*rmdir) (struct inode *,struct dentry *);
Al Viro1a67aaf2011-07-26 01:52:52 -040047 int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -070048 int (*rename) (struct inode *, struct dentry *,
49 struct inode *, struct dentry *);
50 int (*readlink) (struct dentry *, char __user *,int);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010051 void * (*follow_link) (struct dentry *, struct nameidata *);
52 void (*put_link) (struct dentry *, struct nameidata *, void *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070053 void (*truncate) (struct inode *);
Nick Pigginb74c79e2011-01-07 17:49:58 +110054 int (*permission) (struct inode *, int, unsigned int);
Christoph Hellwig4e34e712011-07-23 17:37:31 +020055 int (*get_acl)(struct inode *, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070056 int (*setattr) (struct dentry *, struct iattr *);
57 int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
58 int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
59 ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
60 ssize_t (*listxattr) (struct dentry *, char *, size_t);
61 int (*removexattr) (struct dentry *, const char *);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010062 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
Josef Bacikc3b2da32012-03-26 09:59:21 -040063 void (*update_time)(struct inode *, struct timespec *, int);
Al Virod9585272012-06-22 12:39:14 +040064 int (*atomic_open)(struct inode *, struct dentry *,
Al Viro30d90492012-06-22 12:40:19 +040065 struct file *, unsigned open_flag,
Al Viro47237682012-06-10 05:01:45 -040066 umode_t create_mode, int *opened);
Linus Torvalds1da177e2005-04-16 15:20:36 -070067
68locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010069 all may block
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020070 i_mutex(inode)
Linus Torvalds1da177e2005-04-16 15:20:36 -070071lookup: yes
72create: yes
73link: yes (both)
74mknod: yes
75symlink: yes
76mkdir: yes
77unlink: yes (both)
78rmdir: yes (both) (see below)
79rename: yes (all) (see below)
80readlink: no
81follow_link: no
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010082put_link: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070083setattr: yes
Nick Pigginb74c79e2011-01-07 17:49:58 +110084permission: no (may not block if called in rcu-walk mode)
Christoph Hellwig4e34e712011-07-23 17:37:31 +020085get_acl: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070086getattr: no
87setxattr: yes
88getxattr: no
89listxattr: no
90removexattr: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010091fiemap: no
Josef Bacikc3b2da32012-03-26 09:59:21 -040092update_time: no
Miklos Szeredid18e9002012-06-05 15:10:17 +020093atomic_open: yes
Josef Bacikc3b2da32012-03-26 09:59:21 -040094
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020095 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
Linus Torvalds1da177e2005-04-16 15:20:36 -070096victim.
97 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
Linus Torvalds1da177e2005-04-16 15:20:36 -070098
99See Documentation/filesystems/directory-locking for more detailed discussion
100of the locking scheme for directory operations.
101
102--------------------------- super_operations ---------------------------
103prototypes:
104 struct inode *(*alloc_inode)(struct super_block *sb);
105 void (*destroy_inode)(struct inode *);
Christoph Hellwigaa385722011-05-27 06:53:02 -0400106 void (*dirty_inode) (struct inode *, int flags);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100107 int (*write_inode) (struct inode *, struct writeback_control *wbc);
Al Viro336fb3b2010-06-08 00:37:12 -0400108 int (*drop_inode) (struct inode *);
109 void (*evict_inode) (struct inode *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110 void (*put_super) (struct super_block *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111 int (*sync_fs)(struct super_block *sb, int wait);
Takashi Satoc4be0c12009-01-09 16:40:58 -0800112 int (*freeze_fs) (struct super_block *);
113 int (*unfreeze_fs) (struct super_block *);
David Howells726c3342006-06-23 02:02:58 -0700114 int (*statfs) (struct dentry *, struct kstatfs *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115 int (*remount_fs) (struct super_block *, int *, char *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116 void (*umount_begin) (struct super_block *);
Al Viro34c80b12011-12-08 21:32:45 -0500117 int (*show_options)(struct seq_file *, struct dentry *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
119 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100120 int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121
122locking rules:
Al Viro336fb3b2010-06-08 00:37:12 -0400123 All may block [not true, see below]
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200124 s_umount
125alloc_inode:
126destroy_inode:
Christoph Hellwigaa385722011-05-27 06:53:02 -0400127dirty_inode:
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200128write_inode:
Dave Chinnerf283c862011-03-22 22:23:39 +1100129drop_inode: !!!inode->i_lock!!!
Al Viro336fb3b2010-06-08 00:37:12 -0400130evict_inode:
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200131put_super: write
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200132sync_fs: read
Valerie Aurora06fd5162012-06-12 16:20:48 +0200133freeze_fs: write
134unfreeze_fs: write
Al Viro336fb3b2010-06-08 00:37:12 -0400135statfs: maybe(read) (see below)
136remount_fs: write
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200137umount_begin: no
138show_options: no (namespace_sem)
139quota_read: no (see below)
140quota_write: no (see below)
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100141bdev_try_to_free_page: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700142
Al Viro336fb3b2010-06-08 00:37:12 -0400143->statfs() has s_umount (shared) when called by ustat(2) (native or
144compat), but that's an accident of bad API; s_umount is used to pin
145the superblock down when we only have dev_t given us by userland to
146identify the superblock. Everything else (statfs(), fstatfs(), etc.)
147doesn't hold it when calling ->statfs() - superblock is pinned down
148by resolving the pathname passed to syscall.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700149->quota_read() and ->quota_write() functions are both guaranteed to
150be the only ones operating on the quota file by the quota code (via
151dqio_sem) (unless an admin really wants to screw up something and
152writes to quota files with quotas on). For other details about locking
153see also dquot_operations section.
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100154->bdev_try_to_free_page is called from the ->releasepage handler of
155the block device inode. See there for more details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700156
157--------------------------- file_system_type ---------------------------
158prototypes:
Jonathan Corbet5d8b2eb2006-07-10 04:44:07 -0700159 int (*get_sb) (struct file_system_type *, int,
160 const char *, void *, struct vfsmount *);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100161 struct dentry *(*mount) (struct file_system_type *, int,
162 const char *, void *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163 void (*kill_sb) (struct super_block *);
164locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100165 may block
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100166mount yes
167kill_sb yes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168
Al Viro1a102ff2011-03-16 09:07:58 -0400169->mount() returns ERR_PTR or the root dentry; its superblock should be locked
170on return.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171->kill_sb() takes a write-locked superblock, does all shutdown work on it,
172unlocks and drops the reference.
173
174--------------------------- address_space_operations --------------------------
175prototypes:
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);
Nick Piggin4e02ed42008-10-29 14:00:55 -0700183 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);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189 sector_t (*bmap)(struct address_space *, sector_t);
190 int (*invalidatepage) (struct page *, unsigned long);
191 int (*releasepage) (struct page *, int);
Linus Torvalds6072d132010-12-01 13:35:19 -0500192 void (*freepage)(struct page *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
194 loff_t offset, unsigned long nr_segs);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100195 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 *);
Mel Gorman62c230b2012-07-31 16:44:55 -0700201 int (*swap_activate)(struct file *);
202 int (*swap_deactivate)(struct file *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
204locking rules:
Linus Torvalds6072d132010-12-01 13:35:19 -0500205 All except set_page_dirty and freepage may block
Linus Torvalds1da177e2005-04-16 15:20:36 -0700206
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100207 PageLocked(page) i_mutex
208writepage: yes, unlocks (see below)
209readpage: yes, unlocks
210sync_page: maybe
211writepages:
212set_page_dirty no
213readpages:
214write_begin: locks the page yes
215write_end: yes, unlocks yes
216bmap:
217invalidatepage: yes
218releasepage: yes
219freepage: yes
220direct_IO:
221get_xip_mem: maybe
222migratepage: yes (both)
223launder_page: yes
224is_partially_uptodate: yes
225error_remove_page: yes
Mel Gorman62c230b2012-07-31 16:44:55 -0700226swap_activate: no
227swap_deactivate: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700228
Nick Piggin4e02ed42008-10-29 14:00:55 -0700229 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700230may be called from the request handler (/dev/loop).
231
232 ->readpage() unlocks the page, either synchronously or via I/O
233completion.
234
235 ->readpages() populates the pagecache with the passed pages and starts
236I/O against them. They come unlocked upon I/O completion.
237
238 ->writepage() is used for two purposes: for "memory cleansing" and for
239"sync". These are quite different operations and the behaviour may differ
240depending upon the mode.
241
242If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
243it *must* start I/O against the page, even if that would involve
244blocking on in-progress I/O.
245
246If writepage is called for memory cleansing (sync_mode ==
247WBC_SYNC_NONE) then its role is to get as much writeout underway as
248possible. So writepage should try to avoid blocking against
249currently-in-progress I/O.
250
251If the filesystem is not called for "sync" and it determines that it
252would need to block against in-progress I/O to be able to start new I/O
253against the page the filesystem should redirty the page with
254redirty_page_for_writepage(), then unlock the page and return zero.
255This may also be done to avoid internal deadlocks, but rarely.
256
Robert P. J. Day3a4fa0a2007-10-19 23:10:43 +0200257If the filesystem is called for sync then it must wait on any
Linus Torvalds1da177e2005-04-16 15:20:36 -0700258in-progress I/O and then start new I/O.
259
Nikita Danilov20546062005-05-01 08:58:37 -0700260The filesystem should unlock the page synchronously, before returning to the
261caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
262value. WRITEPAGE_ACTIVATE means that page cannot really be written out
263currently, and VM should stop calling ->writepage() on this page for some
264time. VM does this by moving page to the head of the active list, hence the
265name.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700266
267Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
268and return zero, writepage *must* run set_page_writeback() against the page,
269followed by unlocking it. Once set_page_writeback() has been run against the
270page, write I/O can be submitted and the write I/O completion handler must run
271end_page_writeback() once the I/O is complete. If no I/O is submitted, the
272filesystem must run end_page_writeback() against the page before returning from
273writepage.
274
275That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
276if the filesystem needs the page to be locked during writeout, that is ok, too,
277the page is allowed to be unlocked at any point in time between the calls to
278set_page_writeback() and end_page_writeback().
279
280Note, failure to run either redirty_page_for_writepage() or the combination of
281set_page_writeback()/end_page_writeback() on a page submitted to writepage
282will leave the page itself marked clean but it will be tagged as dirty in the
283radix tree. This incoherency can lead to all sorts of hard-to-debug problems
284in the filesystem like having dirty inodes at umount and losing written data.
285
286 ->sync_page() locking rules are not well-defined - usually it is called
287with lock on page, but that is not guaranteed. Considering the currently
288existing instances of this method ->sync_page() itself doesn't look
289well-defined...
290
291 ->writepages() is used for periodic writeback and for syscall-initiated
292sync operations. The address_space should start I/O against at least
293*nr_to_write pages. *nr_to_write must be decremented for each page which is
294written. The address_space implementation may write more (or less) pages
295than *nr_to_write asks for, but it should try to be reasonably close. If
296nr_to_write is NULL, all dirty pages must be written.
297
298writepages should _only_ write pages which are present on
299mapping->io_pages.
300
301 ->set_page_dirty() is called from various places in the kernel
302when the target page is marked as needing writeback. It may be called
303under spinlock (it cannot block) and is sometimes called with the page
304not locked.
305
306 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100307filesystems and by the swapper. The latter will eventually go away. Please,
308keep it that way and don't breed new callers.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700309
310 ->invalidatepage() is called when the filesystem must attempt to drop
311some or all of the buffers from the page when it is being truncated. It
312returns zero on success. If ->invalidatepage is zero, the kernel uses
313block_invalidatepage() instead.
314
315 ->releasepage() is called when the kernel is about to try to drop the
316buffers from the page in preparation for freeing it. It returns zero to
317indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
318the kernel assumes that the fs has no private interest in the buffers.
319
Linus Torvalds6072d132010-12-01 13:35:19 -0500320 ->freepage() is called when the kernel is done dropping the page
321from the page cache.
322
Trond Myklebuste3db7692007-01-10 23:15:39 -0800323 ->launder_page() may be called prior to releasing a page if
324it is still found to be dirty. It returns zero if the page was successfully
325cleaned, or an error value if not. Note that in order to prevent the page
326getting mapped back in and redirtied, it needs to be kept locked
327across the entire operation.
328
Mel Gorman62c230b2012-07-31 16:44:55 -0700329 ->swap_activate will be called with a non-zero argument on
330files backing (non block device backed) swapfiles. A return value
331of zero indicates success, in which case this file can be used for
332backing swapspace. The swapspace operations will be proxied to the
333address space operations.
334
335 ->swap_deactivate() will be called in the sys_swapoff()
336path after ->swap_activate() returned success.
337
Linus Torvalds1da177e2005-04-16 15:20:36 -0700338----------------------- file_lock_operations ------------------------------
339prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700340 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
341 void (*fl_release_private)(struct file_lock *);
342
343
344locking rules:
Jeff Layton1c8c6012013-06-21 08:58:15 -0400345 inode->i_lock may block
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100346fl_copy_lock: yes no
347fl_release_private: maybe no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348
349----------------------- lock_manager_operations ---------------------------
350prototypes:
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400351 int (*lm_compare_owner)(struct file_lock *, struct file_lock *);
Jeff Layton3999e492013-06-21 08:58:19 -0400352 unsigned long (*lm_owner_key)(struct file_lock *);
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400353 void (*lm_notify)(struct file_lock *); /* unblock callback */
354 int (*lm_grant)(struct file_lock *, struct file_lock *, int);
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400355 void (*lm_break)(struct file_lock *); /* break_lease callback */
356 int (*lm_change)(struct file_lock **, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357
358locking rules:
Jeff Layton1c8c6012013-06-21 08:58:15 -0400359
Jeff Layton7b2296a2013-06-21 08:58:20 -0400360 inode->i_lock blocked_lock_lock may block
361lm_compare_owner: yes[1] maybe no
362lm_owner_key yes[1] yes no
363lm_notify: yes yes no
364lm_grant: no no no
365lm_break: yes no no
366lm_change yes no no
Jeff Layton1c8c6012013-06-21 08:58:15 -0400367
Jeff Layton3999e492013-06-21 08:58:19 -0400368[1]: ->lm_compare_owner and ->lm_owner_key are generally called with
369*an* inode->i_lock held. It may not be the i_lock of the inode
370associated with either file_lock argument! This is the case with deadlock
371detection, since the code has to chase down the owners of locks that may
372be entirely unrelated to the one on which the lock is being acquired.
Jeff Layton7b2296a2013-06-21 08:58:20 -0400373For deadlock detection however, the blocked_lock_lock is also held. The
Jeff Layton3999e492013-06-21 08:58:19 -0400374fact that these locks are held ensures that the file_locks do not
375disappear out from under you while doing the comparison or generating an
376owner key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377
Linus Torvalds1da177e2005-04-16 15:20:36 -0700378--------------------------- buffer_head -----------------------------------
379prototypes:
380 void (*b_end_io)(struct buffer_head *bh, int uptodate);
381
382locking rules:
383 called from interrupts. In other words, extreme care is needed here.
384bh is locked, but that's all warranties we have here. Currently only RAID1,
385highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
386call this method upon the IO completion.
387
388--------------------------- block_device_operations -----------------------
389prototypes:
Christoph Hellwige1455d12010-10-06 10:46:53 +0200390 int (*open) (struct block_device *, fmode_t);
391 int (*release) (struct gendisk *, fmode_t);
392 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
393 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
394 int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700395 int (*media_changed) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200396 void (*unlock_native_capacity) (struct gendisk *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700397 int (*revalidate_disk) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200398 int (*getgeo)(struct block_device *, struct hd_geometry *);
399 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700400
401locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100402 bd_mutex
403open: yes
404release: yes
405ioctl: no
406compat_ioctl: no
407direct_access: no
408media_changed: no
409unlock_native_capacity: no
410revalidate_disk: no
411getgeo: no
412swap_slot_free_notify: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700413
Christoph Hellwige1455d12010-10-06 10:46:53 +0200414media_changed, unlock_native_capacity and revalidate_disk are called only from
415check_disk_change().
416
417swap_slot_free_notify is called with swap_lock and sometimes the page lock
418held.
419
Linus Torvalds1da177e2005-04-16 15:20:36 -0700420
421--------------------------- file_operations -------------------------------
422prototypes:
423 loff_t (*llseek) (struct file *, loff_t, int);
424 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700425 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
Badari Pulavarty027445c2006-09-30 23:28:46 -0700426 ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
427 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
Al Viro2233f312013-05-22 21:44:23 -0400428 int (*iterate) (struct file *, struct dir_context *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700429 unsigned int (*poll) (struct file *, struct poll_table_struct *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700430 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
431 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
432 int (*mmap) (struct file *, struct vm_area_struct *);
433 int (*open) (struct inode *, struct file *);
434 int (*flush) (struct file *);
435 int (*release) (struct inode *, struct file *);
Josef Bacik02c24a82011-07-16 20:44:56 -0400436 int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700437 int (*aio_fsync) (struct kiocb *, int datasync);
438 int (*fasync) (int, struct file *, int);
439 int (*lock) (struct file *, int, struct file_lock *);
440 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
441 loff_t *);
442 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
443 loff_t *);
444 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
445 void __user *);
446 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
447 loff_t *, int);
448 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
449 unsigned long, unsigned long, unsigned long);
450 int (*check_flags)(int);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100451 int (*flock) (struct file *, int, struct file_lock *);
452 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
453 size_t, unsigned int);
454 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
455 size_t, unsigned int);
456 int (*setlease)(struct file *, long, struct file_lock **);
Christoph Hellwig2fe17c12011-01-14 13:07:43 +0100457 long (*fallocate)(struct file *, int, loff_t, loff_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700458};
459
460locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100461 All may block except for ->setlease.
Josef Bacik02c24a82011-07-16 20:44:56 -0400462 No VFS locks held on entry except for ->setlease.
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100463
464->setlease has the file_list_lock held and must not sleep.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700465
466->llseek() locking has moved from llseek to the individual llseek
467implementations. If your fs is not using generic_file_llseek, you
468need to acquire and release the appropriate locks in your ->llseek().
469For many filesystems, it is probably safe to acquire the inode
Jan Blunck866707f2010-05-26 14:44:54 -0700470mutex or just to use i_size_read() instead.
471Note: this does not protect the file->f_pos against concurrent modifications
472since this is something the userspace has to take care about.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700473
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100474->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
475Most instances call fasync_helper(), which does that maintenance, so it's
476not normally something one needs to worry about. Return values > 0 will be
477mapped to zero in the VFS layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700478
479->readdir() and ->ioctl() on directories must be changed. Ideally we would
480move ->readdir() to inode_operations and use a separate method for directory
481->ioctl() or kill the latter completely. One of the problems is that for
482anything that resembles union-mount we won't have a struct file for all
483components. And there are other reasons why the current interface is a mess...
484
Linus Torvalds1da177e2005-04-16 15:20:36 -0700485->read on directories probably must go away - we should just enforce -EISDIR
486in sys_read() and friends.
487
Linus Torvalds1da177e2005-04-16 15:20:36 -0700488--------------------------- dquot_operations -------------------------------
489prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700490 int (*write_dquot) (struct dquot *);
491 int (*acquire_dquot) (struct dquot *);
492 int (*release_dquot) (struct dquot *);
493 int (*mark_dirty) (struct dquot *);
494 int (*write_info) (struct super_block *, int);
495
496These operations are intended to be more or less wrapping functions that ensure
497a proper locking wrt the filesystem and call the generic quota operations.
498
499What filesystem should expect from the generic quota functions:
500
501 FS recursion Held locks when called
Linus Torvalds1da177e2005-04-16 15:20:36 -0700502write_dquot: yes dqonoff_sem or dqptr_sem
503acquire_dquot: yes dqonoff_sem or dqptr_sem
504release_dquot: yes dqonoff_sem or dqptr_sem
505mark_dirty: no -
506write_info: yes dqonoff_sem
507
508FS recursion means calling ->quota_read() and ->quota_write() from superblock
509operations.
510
Linus Torvalds1da177e2005-04-16 15:20:36 -0700511More details about quota locking can be found in fs/dquot.c.
512
513--------------------------- vm_operations_struct -----------------------------
514prototypes:
515 void (*open)(struct vm_area_struct*);
516 void (*close)(struct vm_area_struct*);
Nick Piggind0217ac2007-07-19 01:47:03 -0700517 int (*fault)(struct vm_area_struct*, struct vm_fault *);
Nick Pigginc2ec1752009-03-31 15:23:21 -0700518 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
Rik van Riel28b2ee22008-07-23 21:27:05 -0700519 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700520
521locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100522 mmap_sem PageLocked(page)
523open: yes
524close: yes
525fault: yes can return with page locked
526page_mkwrite: yes can return with page locked
527access: yes
Mark Fashehed2f2f92007-07-19 01:47:01 -0700528
Nick Pigginb827e492009-04-30 15:08:16 -0700529 ->fault() is called when a previously not present pte is about
530to be faulted in. The filesystem must find and return the page associated
531with the passed in "pgoff" in the vm_fault structure. If it is possible that
532the page may be truncated and/or invalidated, then the filesystem must lock
533the page, then ensure it is not already truncated (the page lock will block
534subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
535locked. The VM will unlock the page.
536
537 ->page_mkwrite() is called when a previously read-only pte is
538about to become writeable. The filesystem again must ensure that there are
539no truncate/invalidate races, and then return with the page locked. If
540the page has been truncated, the filesystem should not look up a new page
541like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
542will cause the VM to retry the fault.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700543
Rik van Riel28b2ee22008-07-23 21:27:05 -0700544 ->access() is called when get_user_pages() fails in
545acces_process_vm(), typically used to debug a process through
546/proc/pid/mem or ptrace. This function is needed only for
547VM_IO | VM_PFNMAP VMAs.
548
Linus Torvalds1da177e2005-04-16 15:20:36 -0700549================================================================================
550 Dubious stuff
551
552(if you break something or notice that it is broken and do not fix it yourself
553- at least put it here)