blob: 61b31acb9176b35bc77c914b2b3913abbcc9e78a [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:
Nick Piggin34286d62011-01-07 17:49:57 +110012 int (*d_revalidate)(struct dentry *, struct nameidata *);
Nick Pigginb1e6a012011-01-07 17:49:28 +110013 int (*d_hash)(const struct dentry *, const struct inode *,
14 struct qstr *);
Nick Piggin621e1552011-01-07 17:49:27 +110015 int (*d_compare)(const struct dentry *, const struct inode *,
16 const struct dentry *, const struct inode *,
17 unsigned int, const char *, const struct qstr *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070018 int (*d_delete)(struct dentry *);
19 void (*d_release)(struct dentry *);
20 void (*d_iput)(struct dentry *, struct inode *);
Eric Dumazetc23fbb62007-05-08 00:26:18 -070021 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
David Howells9875cf82011-01-14 18:45:21 +000022 struct vfsmount *(*d_automount)(struct path *path);
David Howellscc53ce52011-01-14 18:45:26 +000023 int (*d_manage)(struct dentry *, bool);
Linus Torvalds1da177e2005-04-16 15:20:36 -070024
25locking rules:
Nick Piggin34286d62011-01-07 17:49:57 +110026 rename_lock ->d_lock may block rcu-walk
27d_revalidate: no no yes (ref-walk) maybe
28d_hash no no no maybe
29d_compare: yes no no maybe
30d_delete: no yes no no
31d_release: no no yes no
32d_iput: no no yes no
33d_dname: no no no no
David Howells9875cf82011-01-14 18:45:21 +000034d_automount: no no yes no
David Howellsab909112011-01-14 18:46:51 +000035d_manage: no no yes (ref-walk) maybe
Linus Torvalds1da177e2005-04-16 15:20:36 -070036
37--------------------------- inode_operations ---------------------------
38prototypes:
39 int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
40 struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
41ata *);
42 int (*link) (struct dentry *,struct inode *,struct dentry *);
43 int (*unlink) (struct inode *,struct dentry *);
44 int (*symlink) (struct inode *,struct dentry *,const char *);
45 int (*mkdir) (struct inode *,struct dentry *,int);
46 int (*rmdir) (struct inode *,struct dentry *);
47 int (*mknod) (struct inode *,struct dentry *,int,dev_t);
48 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);
55 int (*check_acl)(struct inode *, int, unsigned 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 void (*truncate_range)(struct inode *, loff_t, loff_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010063 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
Linus Torvalds1da177e2005-04-16 15:20:36 -070064
65locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010066 all may block
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020067 i_mutex(inode)
Linus Torvalds1da177e2005-04-16 15:20:36 -070068lookup: yes
69create: yes
70link: yes (both)
71mknod: yes
72symlink: yes
73mkdir: yes
74unlink: yes (both)
75rmdir: yes (both) (see below)
76rename: yes (all) (see below)
77readlink: no
78follow_link: no
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010079put_link: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070080truncate: yes (see below)
81setattr: yes
Nick Pigginb74c79e2011-01-07 17:49:58 +110082permission: no (may not block if called in rcu-walk mode)
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010083check_acl: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070084getattr: no
85setxattr: yes
86getxattr: no
87listxattr: no
88removexattr: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010089truncate_range: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010090fiemap: no
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020091 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
Linus Torvalds1da177e2005-04-16 15:20:36 -070092victim.
93 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
94 ->truncate() is never called directly - it's a callback, not a
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010095method. It's called by vmtruncate() - deprecated library function used by
Linus Torvalds1da177e2005-04-16 15:20:36 -070096->setattr(). Locking information above applies to that call (i.e. is
97inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
98passed).
99
100See Documentation/filesystems/directory-locking for more detailed discussion
101of the locking scheme for directory operations.
102
103--------------------------- super_operations ---------------------------
104prototypes:
105 struct inode *(*alloc_inode)(struct super_block *sb);
106 void (*destroy_inode)(struct inode *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107 void (*dirty_inode) (struct inode *);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100108 int (*write_inode) (struct inode *, struct writeback_control *wbc);
Al Viro336fb3b2010-06-08 00:37:12 -0400109 int (*drop_inode) (struct inode *);
110 void (*evict_inode) (struct inode *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111 void (*put_super) (struct super_block *);
112 void (*write_super) (struct super_block *);
113 int (*sync_fs)(struct super_block *sb, int wait);
Takashi Satoc4be0c12009-01-09 16:40:58 -0800114 int (*freeze_fs) (struct super_block *);
115 int (*unfreeze_fs) (struct super_block *);
David Howells726c3342006-06-23 02:02:58 -0700116 int (*statfs) (struct dentry *, struct kstatfs *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117 int (*remount_fs) (struct super_block *, int *, char *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118 void (*umount_begin) (struct super_block *);
119 int (*show_options)(struct seq_file *, struct vfsmount *);
120 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
121 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100122 int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700123
124locking rules:
Al Viro336fb3b2010-06-08 00:37:12 -0400125 All may block [not true, see below]
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200126 s_umount
127alloc_inode:
128destroy_inode:
129dirty_inode: (must not sleep)
130write_inode:
Dave Chinnerf283c862011-03-22 22:23:39 +1100131drop_inode: !!!inode->i_lock!!!
Al Viro336fb3b2010-06-08 00:37:12 -0400132evict_inode:
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200133put_super: write
134write_super: read
135sync_fs: read
136freeze_fs: read
137unfreeze_fs: read
Al Viro336fb3b2010-06-08 00:37:12 -0400138statfs: maybe(read) (see below)
139remount_fs: write
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200140umount_begin: no
141show_options: no (namespace_sem)
142quota_read: no (see below)
143quota_write: no (see below)
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100144bdev_try_to_free_page: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145
Al Viro336fb3b2010-06-08 00:37:12 -0400146->statfs() has s_umount (shared) when called by ustat(2) (native or
147compat), but that's an accident of bad API; s_umount is used to pin
148the superblock down when we only have dev_t given us by userland to
149identify the superblock. Everything else (statfs(), fstatfs(), etc.)
150doesn't hold it when calling ->statfs() - superblock is pinned down
151by resolving the pathname passed to syscall.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152->quota_read() and ->quota_write() functions are both guaranteed to
153be the only ones operating on the quota file by the quota code (via
154dqio_sem) (unless an admin really wants to screw up something and
155writes to quota files with quotas on). For other details about locking
156see also dquot_operations section.
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100157->bdev_try_to_free_page is called from the ->releasepage handler of
158the block device inode. See there for more details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159
160--------------------------- file_system_type ---------------------------
161prototypes:
Jonathan Corbet5d8b2eb2006-07-10 04:44:07 -0700162 int (*get_sb) (struct file_system_type *, int,
163 const char *, void *, struct vfsmount *);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100164 struct dentry *(*mount) (struct file_system_type *, int,
165 const char *, void *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166 void (*kill_sb) (struct super_block *);
167locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100168 may block
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100169mount yes
170kill_sb yes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
Al Viro1a102ff2011-03-16 09:07:58 -0400172->mount() returns ERR_PTR or the root dentry; its superblock should be locked
173on return.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174->kill_sb() takes a write-locked superblock, does all shutdown work on it,
175unlocks and drops the reference.
176
177--------------------------- address_space_operations --------------------------
178prototypes:
179 int (*writepage)(struct page *page, struct writeback_control *wbc);
180 int (*readpage)(struct file *, struct page *);
181 int (*sync_page)(struct page *);
182 int (*writepages)(struct address_space *, struct writeback_control *);
183 int (*set_page_dirty)(struct page *page);
184 int (*readpages)(struct file *filp, struct address_space *mapping,
185 struct list_head *pages, unsigned nr_pages);
Nick Piggin4e02ed42008-10-29 14:00:55 -0700186 int (*write_begin)(struct file *, struct address_space *mapping,
187 loff_t pos, unsigned len, unsigned flags,
188 struct page **pagep, void **fsdata);
189 int (*write_end)(struct file *, struct address_space *mapping,
190 loff_t pos, unsigned len, unsigned copied,
191 struct page *page, void *fsdata);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192 sector_t (*bmap)(struct address_space *, sector_t);
193 int (*invalidatepage) (struct page *, unsigned long);
194 int (*releasepage) (struct page *, int);
Linus Torvalds6072d132010-12-01 13:35:19 -0500195 void (*freepage)(struct page *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700196 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
197 loff_t offset, unsigned long nr_segs);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100198 int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
199 unsigned long *);
200 int (*migratepage)(struct address_space *, struct page *, struct page *);
201 int (*launder_page)(struct page *);
202 int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
203 int (*error_remove_page)(struct address_space *, struct page *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700204
205locking rules:
Linus Torvalds6072d132010-12-01 13:35:19 -0500206 All except set_page_dirty and freepage may block
Linus Torvalds1da177e2005-04-16 15:20:36 -0700207
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100208 PageLocked(page) i_mutex
209writepage: yes, unlocks (see below)
210readpage: yes, unlocks
211sync_page: maybe
212writepages:
213set_page_dirty no
214readpages:
215write_begin: locks the page yes
216write_end: yes, unlocks yes
217bmap:
218invalidatepage: yes
219releasepage: yes
220freepage: yes
221direct_IO:
222get_xip_mem: maybe
223migratepage: yes (both)
224launder_page: yes
225is_partially_uptodate: yes
226error_remove_page: yes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700227
Nick Piggin4e02ed42008-10-29 14:00:55 -0700228 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700229may be called from the request handler (/dev/loop).
230
231 ->readpage() unlocks the page, either synchronously or via I/O
232completion.
233
234 ->readpages() populates the pagecache with the passed pages and starts
235I/O against them. They come unlocked upon I/O completion.
236
237 ->writepage() is used for two purposes: for "memory cleansing" and for
238"sync". These are quite different operations and the behaviour may differ
239depending upon the mode.
240
241If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
242it *must* start I/O against the page, even if that would involve
243blocking on in-progress I/O.
244
245If writepage is called for memory cleansing (sync_mode ==
246WBC_SYNC_NONE) then its role is to get as much writeout underway as
247possible. So writepage should try to avoid blocking against
248currently-in-progress I/O.
249
250If the filesystem is not called for "sync" and it determines that it
251would need to block against in-progress I/O to be able to start new I/O
252against the page the filesystem should redirty the page with
253redirty_page_for_writepage(), then unlock the page and return zero.
254This may also be done to avoid internal deadlocks, but rarely.
255
Robert P. J. Day3a4fa0a2007-10-19 23:10:43 +0200256If the filesystem is called for sync then it must wait on any
Linus Torvalds1da177e2005-04-16 15:20:36 -0700257in-progress I/O and then start new I/O.
258
Nikita Danilov20546062005-05-01 08:58:37 -0700259The filesystem should unlock the page synchronously, before returning to the
260caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
261value. WRITEPAGE_ACTIVATE means that page cannot really be written out
262currently, and VM should stop calling ->writepage() on this page for some
263time. VM does this by moving page to the head of the active list, hence the
264name.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700265
266Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
267and return zero, writepage *must* run set_page_writeback() against the page,
268followed by unlocking it. Once set_page_writeback() has been run against the
269page, write I/O can be submitted and the write I/O completion handler must run
270end_page_writeback() once the I/O is complete. If no I/O is submitted, the
271filesystem must run end_page_writeback() against the page before returning from
272writepage.
273
274That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
275if the filesystem needs the page to be locked during writeout, that is ok, too,
276the page is allowed to be unlocked at any point in time between the calls to
277set_page_writeback() and end_page_writeback().
278
279Note, failure to run either redirty_page_for_writepage() or the combination of
280set_page_writeback()/end_page_writeback() on a page submitted to writepage
281will leave the page itself marked clean but it will be tagged as dirty in the
282radix tree. This incoherency can lead to all sorts of hard-to-debug problems
283in the filesystem like having dirty inodes at umount and losing written data.
284
285 ->sync_page() locking rules are not well-defined - usually it is called
286with lock on page, but that is not guaranteed. Considering the currently
287existing instances of this method ->sync_page() itself doesn't look
288well-defined...
289
290 ->writepages() is used for periodic writeback and for syscall-initiated
291sync operations. The address_space should start I/O against at least
292*nr_to_write pages. *nr_to_write must be decremented for each page which is
293written. The address_space implementation may write more (or less) pages
294than *nr_to_write asks for, but it should try to be reasonably close. If
295nr_to_write is NULL, all dirty pages must be written.
296
297writepages should _only_ write pages which are present on
298mapping->io_pages.
299
300 ->set_page_dirty() is called from various places in the kernel
301when the target page is marked as needing writeback. It may be called
302under spinlock (it cannot block) and is sometimes called with the page
303not locked.
304
305 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100306filesystems and by the swapper. The latter will eventually go away. Please,
307keep it that way and don't breed new callers.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700308
309 ->invalidatepage() is called when the filesystem must attempt to drop
310some or all of the buffers from the page when it is being truncated. It
311returns zero on success. If ->invalidatepage is zero, the kernel uses
312block_invalidatepage() instead.
313
314 ->releasepage() is called when the kernel is about to try to drop the
315buffers from the page in preparation for freeing it. It returns zero to
316indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
317the kernel assumes that the fs has no private interest in the buffers.
318
Linus Torvalds6072d132010-12-01 13:35:19 -0500319 ->freepage() is called when the kernel is done dropping the page
320from the page cache.
321
Trond Myklebuste3db7692007-01-10 23:15:39 -0800322 ->launder_page() may be called prior to releasing a page if
323it is still found to be dirty. It returns zero if the page was successfully
324cleaned, or an error value if not. Note that in order to prevent the page
325getting mapped back in and redirtied, it needs to be kept locked
326across the entire operation.
327
Linus Torvalds1da177e2005-04-16 15:20:36 -0700328----------------------- file_lock_operations ------------------------------
329prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
331 void (*fl_release_private)(struct file_lock *);
332
333
334locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100335 file_lock_lock may block
336fl_copy_lock: yes no
337fl_release_private: maybe no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700338
339----------------------- lock_manager_operations ---------------------------
340prototypes:
341 int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
342 void (*fl_notify)(struct file_lock *); /* unblock callback */
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100343 int (*fl_grant)(struct file_lock *, struct file_lock *, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700344 void (*fl_release_private)(struct file_lock *);
345 void (*fl_break)(struct file_lock *); /* break_lease callback */
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100346 int (*fl_change)(struct file_lock **, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700347
348locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100349 file_lock_lock may block
350fl_compare_owner: yes no
351fl_notify: yes no
352fl_grant: no no
353fl_release_private: maybe no
354fl_break: yes no
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100355fl_change yes no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700356
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357--------------------------- buffer_head -----------------------------------
358prototypes:
359 void (*b_end_io)(struct buffer_head *bh, int uptodate);
360
361locking rules:
362 called from interrupts. In other words, extreme care is needed here.
363bh is locked, but that's all warranties we have here. Currently only RAID1,
364highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
365call this method upon the IO completion.
366
367--------------------------- block_device_operations -----------------------
368prototypes:
Christoph Hellwige1455d12010-10-06 10:46:53 +0200369 int (*open) (struct block_device *, fmode_t);
370 int (*release) (struct gendisk *, fmode_t);
371 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
372 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
373 int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700374 int (*media_changed) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200375 void (*unlock_native_capacity) (struct gendisk *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700376 int (*revalidate_disk) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200377 int (*getgeo)(struct block_device *, struct hd_geometry *);
378 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700379
380locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100381 bd_mutex
382open: yes
383release: yes
384ioctl: no
385compat_ioctl: no
386direct_access: no
387media_changed: no
388unlock_native_capacity: no
389revalidate_disk: no
390getgeo: no
391swap_slot_free_notify: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700392
Christoph Hellwige1455d12010-10-06 10:46:53 +0200393media_changed, unlock_native_capacity and revalidate_disk are called only from
394check_disk_change().
395
396swap_slot_free_notify is called with swap_lock and sometimes the page lock
397held.
398
Linus Torvalds1da177e2005-04-16 15:20:36 -0700399
400--------------------------- file_operations -------------------------------
401prototypes:
402 loff_t (*llseek) (struct file *, loff_t, int);
403 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700404 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
Badari Pulavarty027445c2006-09-30 23:28:46 -0700405 ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
406 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700407 int (*readdir) (struct file *, void *, filldir_t);
408 unsigned int (*poll) (struct file *, struct poll_table_struct *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700409 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
410 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
411 int (*mmap) (struct file *, struct vm_area_struct *);
412 int (*open) (struct inode *, struct file *);
413 int (*flush) (struct file *);
414 int (*release) (struct inode *, struct file *);
Christoph Hellwig7ea80852010-05-26 17:53:25 +0200415 int (*fsync) (struct file *, int datasync);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700416 int (*aio_fsync) (struct kiocb *, int datasync);
417 int (*fasync) (int, struct file *, int);
418 int (*lock) (struct file *, int, struct file_lock *);
419 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
420 loff_t *);
421 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
422 loff_t *);
423 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
424 void __user *);
425 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
426 loff_t *, int);
427 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
428 unsigned long, unsigned long, unsigned long);
429 int (*check_flags)(int);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100430 int (*flock) (struct file *, int, struct file_lock *);
431 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
432 size_t, unsigned int);
433 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
434 size_t, unsigned int);
435 int (*setlease)(struct file *, long, struct file_lock **);
Christoph Hellwig2fe17c12011-01-14 13:07:43 +0100436 long (*fallocate)(struct file *, int, loff_t, loff_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700437};
438
439locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100440 All may block except for ->setlease.
441 No VFS locks held on entry except for ->fsync and ->setlease.
442
443->fsync() has i_mutex on inode.
444
445->setlease has the file_list_lock held and must not sleep.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700446
447->llseek() locking has moved from llseek to the individual llseek
448implementations. If your fs is not using generic_file_llseek, you
449need to acquire and release the appropriate locks in your ->llseek().
450For many filesystems, it is probably safe to acquire the inode
Jan Blunck866707f2010-05-26 14:44:54 -0700451mutex or just to use i_size_read() instead.
452Note: this does not protect the file->f_pos against concurrent modifications
453since this is something the userspace has to take care about.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700454
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100455->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
456Most instances call fasync_helper(), which does that maintenance, so it's
457not normally something one needs to worry about. Return values > 0 will be
458mapped to zero in the VFS layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700459
460->readdir() and ->ioctl() on directories must be changed. Ideally we would
461move ->readdir() to inode_operations and use a separate method for directory
462->ioctl() or kill the latter completely. One of the problems is that for
463anything that resembles union-mount we won't have a struct file for all
464components. And there are other reasons why the current interface is a mess...
465
Linus Torvalds1da177e2005-04-16 15:20:36 -0700466->read on directories probably must go away - we should just enforce -EISDIR
467in sys_read() and friends.
468
Linus Torvalds1da177e2005-04-16 15:20:36 -0700469--------------------------- dquot_operations -------------------------------
470prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700471 int (*write_dquot) (struct dquot *);
472 int (*acquire_dquot) (struct dquot *);
473 int (*release_dquot) (struct dquot *);
474 int (*mark_dirty) (struct dquot *);
475 int (*write_info) (struct super_block *, int);
476
477These operations are intended to be more or less wrapping functions that ensure
478a proper locking wrt the filesystem and call the generic quota operations.
479
480What filesystem should expect from the generic quota functions:
481
482 FS recursion Held locks when called
Linus Torvalds1da177e2005-04-16 15:20:36 -0700483write_dquot: yes dqonoff_sem or dqptr_sem
484acquire_dquot: yes dqonoff_sem or dqptr_sem
485release_dquot: yes dqonoff_sem or dqptr_sem
486mark_dirty: no -
487write_info: yes dqonoff_sem
488
489FS recursion means calling ->quota_read() and ->quota_write() from superblock
490operations.
491
Linus Torvalds1da177e2005-04-16 15:20:36 -0700492More details about quota locking can be found in fs/dquot.c.
493
494--------------------------- vm_operations_struct -----------------------------
495prototypes:
496 void (*open)(struct vm_area_struct*);
497 void (*close)(struct vm_area_struct*);
Nick Piggind0217ac2007-07-19 01:47:03 -0700498 int (*fault)(struct vm_area_struct*, struct vm_fault *);
Nick Pigginc2ec1752009-03-31 15:23:21 -0700499 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
Rik van Riel28b2ee22008-07-23 21:27:05 -0700500 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700501
502locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100503 mmap_sem PageLocked(page)
504open: yes
505close: yes
506fault: yes can return with page locked
507page_mkwrite: yes can return with page locked
508access: yes
Mark Fashehed2f2f92007-07-19 01:47:01 -0700509
Nick Pigginb827e492009-04-30 15:08:16 -0700510 ->fault() is called when a previously not present pte is about
511to be faulted in. The filesystem must find and return the page associated
512with the passed in "pgoff" in the vm_fault structure. If it is possible that
513the page may be truncated and/or invalidated, then the filesystem must lock
514the page, then ensure it is not already truncated (the page lock will block
515subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
516locked. The VM will unlock the page.
517
518 ->page_mkwrite() is called when a previously read-only pte is
519about to become writeable. The filesystem again must ensure that there are
520no truncate/invalidate races, and then return with the page locked. If
521the page has been truncated, the filesystem should not look up a new page
522like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
523will cause the VM to retry the fault.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700524
Rik van Riel28b2ee22008-07-23 21:27:05 -0700525 ->access() is called when get_user_pages() fails in
526acces_process_vm(), typically used to debug a process through
527/proc/pid/mem or ptrace. This function is needed only for
528VM_IO | VM_PFNMAP VMAs.
529
Linus Torvalds1da177e2005-04-16 15:20:36 -0700530================================================================================
531 Dubious stuff
532
533(if you break something or notice that it is broken and do not fix it yourself
534- at least put it here)