blob: 1b5f15653b1bb82ca0fc7801fe01fe8c4c75047a [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:
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 *);
Al Viro6fa67e72016-07-31 16:37:25 -040015 int (*d_compare)(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 *);
Miklos Szeredi285b1022016-06-28 11:47:32 +020018 int (*d_init)(struct dentry *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070019 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);
Miklos Szeredie698b8a2016-06-30 08:53:27 +020024 struct dentry *(*d_real)(struct dentry *, const struct inode *,
25 unsigned int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070026
27locking rules:
Nick Piggin34286d62011-01-07 17:49:57 +110028 rename_lock ->d_lock may block rcu-walk
29d_revalidate: no no yes (ref-walk) maybe
Jeff Laytonecf3d1f2013-02-20 11:19:05 -050030d_weak_revalidate:no no yes no
Nick Piggin34286d62011-01-07 17:49:57 +110031d_hash no no no maybe
32d_compare: yes no no maybe
33d_delete: no yes no no
Miklos Szeredi285b1022016-06-28 11:47:32 +020034d_init: no no yes no
Nick Piggin34286d62011-01-07 17:49:57 +110035d_release: no no yes no
Sage Weilf0023bc2011-10-28 10:02:42 -070036d_prune: no yes no no
Nick Piggin34286d62011-01-07 17:49:57 +110037d_iput: no no yes no
38d_dname: no no no no
David Howells9875cf82011-01-14 18:45:21 +000039d_automount: no no yes no
David Howellsab909112011-01-14 18:46:51 +000040d_manage: no no yes (ref-walk) maybe
Miklos Szeredie698b8a2016-06-30 08:53:27 +020041d_real no no yes no
Linus Torvalds1da177e2005-04-16 15:20:36 -070042
43--------------------------- inode_operations ---------------------------
44prototypes:
Al Viroebfc3b42012-06-10 18:05:36 -040045 int (*create) (struct inode *,struct dentry *,umode_t, bool);
Al Viro00cd8dd2012-06-10 17:13:09 -040046 struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070047 int (*link) (struct dentry *,struct inode *,struct dentry *);
48 int (*unlink) (struct inode *,struct dentry *);
49 int (*symlink) (struct inode *,struct dentry *,const char *);
Al Viro18bb1db2011-07-26 01:41:39 -040050 int (*mkdir) (struct inode *,struct dentry *,umode_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -070051 int (*rmdir) (struct inode *,struct dentry *);
Al Viro1a67aaf2011-07-26 01:52:52 -040052 int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -070053 int (*rename) (struct inode *, struct dentry *,
Miklos Szeredi520c8b12014-04-01 17:08:42 +020054 struct inode *, struct dentry *, unsigned int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070055 int (*readlink) (struct dentry *, char __user *,int);
Al Viro6b255392015-11-17 10:20:54 -050056 const char *(*get_link) (struct dentry *, struct inode *, void **);
Linus Torvalds1da177e2005-04-16 15:20:36 -070057 void (*truncate) (struct inode *);
Nick Pigginb74c79e2011-01-07 17:49:58 +110058 int (*permission) (struct inode *, int, unsigned int);
Christoph Hellwig4e34e712011-07-23 17:37:31 +020059 int (*get_acl)(struct inode *, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -070060 int (*setattr) (struct dentry *, struct iattr *);
61 int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
Linus Torvalds1da177e2005-04-16 15:20:36 -070062 ssize_t (*listxattr) (struct dentry *, char *, size_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010063 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
Josef Bacikc3b2da32012-03-26 09:59:21 -040064 void (*update_time)(struct inode *, struct timespec *, int);
Al Virod9585272012-06-22 12:39:14 +040065 int (*atomic_open)(struct inode *, struct dentry *,
Al Viro30d90492012-06-22 12:40:19 +040066 struct file *, unsigned open_flag,
Al Viro47237682012-06-10 05:01:45 -040067 umode_t create_mode, int *opened);
Al Viro48bde8d2013-07-03 16:19:23 +040068 int (*tmpfile) (struct inode *, struct dentry *, umode_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -070069
70locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010071 all may block
Artem Bityutskiya7bc02f2007-05-09 07:53:16 +020072 i_mutex(inode)
Linus Torvalds1da177e2005-04-16 15:20:36 -070073lookup: yes
74create: yes
75link: yes (both)
76mknod: yes
77symlink: yes
78mkdir: yes
79unlink: yes (both)
80rmdir: yes (both) (see below)
Miklos Szeredi2773bf02016-09-27 11:03:58 +020081rename: yes (all) (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -070082readlink: no
Al Viro6b255392015-11-17 10:20:54 -050083get_link: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070084setattr: yes
Nick Pigginb74c79e2011-01-07 17:49:58 +110085permission: no (may not block if called in rcu-walk mode)
Christoph Hellwig4e34e712011-07-23 17:37:31 +020086get_acl: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070087getattr: no
Linus Torvalds1da177e2005-04-16 15:20:36 -070088listxattr: no
Christoph Hellwigb83be6f2010-12-16 12:04:54 +010089fiemap: no
Josef Bacikc3b2da32012-03-26 09:59:21 -040090update_time: no
Miklos Szeredid18e9002012-06-05 15:10:17 +020091atomic_open: yes
Al Viro48bde8d2013-07-03 16:19:23 +040092tmpfile: no
Josef Bacikc3b2da32012-03-26 09:59:21 -040093
Andreas Gruenbacher6c6ef9f2016-09-29 17:48:44 +020094
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.
Miklos Szeredi2773bf02016-09-27 11:03:58 +020097 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
Andreas Gruenbacher6c6ef9f2016-09-29 17:48:44 +0200102----------------------- xattr_handler operations -----------------------
103prototypes:
104 bool (*list)(struct dentry *dentry);
105 int (*get)(const struct xattr_handler *handler, struct dentry *dentry,
106 struct inode *inode, const char *name, void *buffer,
107 size_t size);
108 int (*set)(const struct xattr_handler *handler, struct dentry *dentry,
109 struct inode *inode, const char *name, const void *buffer,
110 size_t size, int flags);
111
112locking rules:
113 all may block
114 i_mutex(inode)
115list: no
116get: no
117set: yes
118
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119--------------------------- super_operations ---------------------------
120prototypes:
121 struct inode *(*alloc_inode)(struct super_block *sb);
122 void (*destroy_inode)(struct inode *);
Christoph Hellwigaa385722011-05-27 06:53:02 -0400123 void (*dirty_inode) (struct inode *, int flags);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100124 int (*write_inode) (struct inode *, struct writeback_control *wbc);
Al Viro336fb3b2010-06-08 00:37:12 -0400125 int (*drop_inode) (struct inode *);
126 void (*evict_inode) (struct inode *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127 void (*put_super) (struct super_block *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700128 int (*sync_fs)(struct super_block *sb, int wait);
Takashi Satoc4be0c12009-01-09 16:40:58 -0800129 int (*freeze_fs) (struct super_block *);
130 int (*unfreeze_fs) (struct super_block *);
David Howells726c3342006-06-23 02:02:58 -0700131 int (*statfs) (struct dentry *, struct kstatfs *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132 int (*remount_fs) (struct super_block *, int *, char *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133 void (*umount_begin) (struct super_block *);
Al Viro34c80b12011-12-08 21:32:45 -0500134 int (*show_options)(struct seq_file *, struct dentry *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700135 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
136 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100137 int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
139locking rules:
Al Viro336fb3b2010-06-08 00:37:12 -0400140 All may block [not true, see below]
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200141 s_umount
142alloc_inode:
143destroy_inode:
Christoph Hellwigaa385722011-05-27 06:53:02 -0400144dirty_inode:
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200145write_inode:
Dave Chinnerf283c862011-03-22 22:23:39 +1100146drop_inode: !!!inode->i_lock!!!
Al Viro336fb3b2010-06-08 00:37:12 -0400147evict_inode:
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200148put_super: write
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200149sync_fs: read
Valerie Aurora06fd5162012-06-12 16:20:48 +0200150freeze_fs: write
151unfreeze_fs: write
Al Viro336fb3b2010-06-08 00:37:12 -0400152statfs: maybe(read) (see below)
153remount_fs: write
Christoph Hellwig7e325d32009-06-19 20:22:37 +0200154umount_begin: no
155show_options: no (namespace_sem)
156quota_read: no (see below)
157quota_write: no (see below)
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100158bdev_try_to_free_page: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159
Al Viro336fb3b2010-06-08 00:37:12 -0400160->statfs() has s_umount (shared) when called by ustat(2) (native or
161compat), but that's an accident of bad API; s_umount is used to pin
162the superblock down when we only have dev_t given us by userland to
163identify the superblock. Everything else (statfs(), fstatfs(), etc.)
164doesn't hold it when calling ->statfs() - superblock is pinned down
165by resolving the pathname passed to syscall.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166->quota_read() and ->quota_write() functions are both guaranteed to
167be the only ones operating on the quota file by the quota code (via
168dqio_sem) (unless an admin really wants to screw up something and
169writes to quota files with quotas on). For other details about locking
170see also dquot_operations section.
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100171->bdev_try_to_free_page is called from the ->releasepage handler of
172the block device inode. See there for more details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700173
174--------------------------- file_system_type ---------------------------
175prototypes:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100176 struct dentry *(*mount) (struct file_system_type *, int,
177 const char *, void *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178 void (*kill_sb) (struct super_block *);
179locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100180 may block
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100181mount yes
182kill_sb yes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183
Al Viro1a102ff2011-03-16 09:07:58 -0400184->mount() returns ERR_PTR or the root dentry; its superblock should be locked
185on return.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186->kill_sb() takes a write-locked superblock, does all shutdown work on it,
187unlocks and drops the reference.
188
189--------------------------- address_space_operations --------------------------
190prototypes:
191 int (*writepage)(struct page *page, struct writeback_control *wbc);
192 int (*readpage)(struct file *, struct page *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193 int (*writepages)(struct address_space *, struct writeback_control *);
194 int (*set_page_dirty)(struct page *page);
195 int (*readpages)(struct file *filp, struct address_space *mapping,
196 struct list_head *pages, unsigned nr_pages);
Nick Piggin4e02ed42008-10-29 14:00:55 -0700197 int (*write_begin)(struct file *, struct address_space *mapping,
198 loff_t pos, unsigned len, unsigned flags,
199 struct page **pagep, void **fsdata);
200 int (*write_end)(struct file *, struct address_space *mapping,
201 loff_t pos, unsigned len, unsigned copied,
202 struct page *page, void *fsdata);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203 sector_t (*bmap)(struct address_space *, sector_t);
Lukas Czernerd47992f2013-05-21 23:17:23 -0400204 void (*invalidatepage) (struct page *, unsigned int, unsigned int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205 int (*releasepage) (struct page *, int);
Linus Torvalds6072d132010-12-01 13:35:19 -0500206 void (*freepage)(struct page *);
Christoph Hellwigc8b8e322016-04-07 08:51:58 -0700207 int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
Minchan Kimbda807d2016-07-26 15:23:05 -0700208 bool (*isolate_page) (struct page *, isolate_mode_t);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100209 int (*migratepage)(struct address_space *, struct page *, struct page *);
Minchan Kimbda807d2016-07-26 15:23:05 -0700210 void (*putback_page) (struct page *);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100211 int (*launder_page)(struct page *);
Al Viroc186afb42014-02-02 21:16:54 -0500212 int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100213 int (*error_remove_page)(struct address_space *, struct page *);
Mel Gorman62c230b2012-07-31 16:44:55 -0700214 int (*swap_activate)(struct file *);
215 int (*swap_deactivate)(struct file *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700216
217locking rules:
Linus Torvalds6072d132010-12-01 13:35:19 -0500218 All except set_page_dirty and freepage may block
Linus Torvalds1da177e2005-04-16 15:20:36 -0700219
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100220 PageLocked(page) i_mutex
221writepage: yes, unlocks (see below)
222readpage: yes, unlocks
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100223writepages:
224set_page_dirty no
225readpages:
226write_begin: locks the page yes
227write_end: yes, unlocks yes
228bmap:
229invalidatepage: yes
230releasepage: yes
231freepage: yes
232direct_IO:
Minchan Kimbda807d2016-07-26 15:23:05 -0700233isolate_page: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100234migratepage: yes (both)
Minchan Kimbda807d2016-07-26 15:23:05 -0700235putback_page: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100236launder_page: yes
237is_partially_uptodate: yes
238error_remove_page: yes
Mel Gorman62c230b2012-07-31 16:44:55 -0700239swap_activate: no
240swap_deactivate: no
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241
Matthew Wilcoxf4e6d8442016-03-06 23:27:26 -0500242 ->write_begin(), ->write_end() and ->readpage() may be called from
243the request handler (/dev/loop).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700244
245 ->readpage() unlocks the page, either synchronously or via I/O
246completion.
247
248 ->readpages() populates the pagecache with the passed pages and starts
249I/O against them. They come unlocked upon I/O completion.
250
251 ->writepage() is used for two purposes: for "memory cleansing" and for
252"sync". These are quite different operations and the behaviour may differ
253depending upon the mode.
254
255If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
256it *must* start I/O against the page, even if that would involve
257blocking on in-progress I/O.
258
259If writepage is called for memory cleansing (sync_mode ==
260WBC_SYNC_NONE) then its role is to get as much writeout underway as
261possible. So writepage should try to avoid blocking against
262currently-in-progress I/O.
263
264If the filesystem is not called for "sync" and it determines that it
265would need to block against in-progress I/O to be able to start new I/O
266against the page the filesystem should redirty the page with
267redirty_page_for_writepage(), then unlock the page and return zero.
268This may also be done to avoid internal deadlocks, but rarely.
269
Robert P. J. Day3a4fa0a2007-10-19 23:10:43 +0200270If the filesystem is called for sync then it must wait on any
Linus Torvalds1da177e2005-04-16 15:20:36 -0700271in-progress I/O and then start new I/O.
272
Nikita Danilov20546062005-05-01 08:58:37 -0700273The filesystem should unlock the page synchronously, before returning to the
274caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
275value. WRITEPAGE_ACTIVATE means that page cannot really be written out
276currently, and VM should stop calling ->writepage() on this page for some
277time. VM does this by moving page to the head of the active list, hence the
278name.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700279
280Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
281and return zero, writepage *must* run set_page_writeback() against the page,
282followed by unlocking it. Once set_page_writeback() has been run against the
283page, write I/O can be submitted and the write I/O completion handler must run
284end_page_writeback() once the I/O is complete. If no I/O is submitted, the
285filesystem must run end_page_writeback() against the page before returning from
286writepage.
287
288That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
289if the filesystem needs the page to be locked during writeout, that is ok, too,
290the page is allowed to be unlocked at any point in time between the calls to
291set_page_writeback() and end_page_writeback().
292
293Note, failure to run either redirty_page_for_writepage() or the combination of
294set_page_writeback()/end_page_writeback() on a page submitted to writepage
295will leave the page itself marked clean but it will be tagged as dirty in the
296radix tree. This incoherency can lead to all sorts of hard-to-debug problems
297in the filesystem like having dirty inodes at umount and losing written data.
298
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299 ->writepages() is used for periodic writeback and for syscall-initiated
300sync operations. The address_space should start I/O against at least
301*nr_to_write pages. *nr_to_write must be decremented for each page which is
302written. The address_space implementation may write more (or less) pages
303than *nr_to_write asks for, but it should try to be reasonably close. If
304nr_to_write is NULL, all dirty pages must be written.
305
306writepages should _only_ write pages which are present on
307mapping->io_pages.
308
309 ->set_page_dirty() is called from various places in the kernel
310when the target page is marked as needing writeback. It may be called
311under spinlock (it cannot block) and is sometimes called with the page
312not locked.
313
314 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100315filesystems and by the swapper. The latter will eventually go away. Please,
316keep it that way and don't breed new callers.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317
318 ->invalidatepage() is called when the filesystem must attempt to drop
Lukas Czernerd47992f2013-05-21 23:17:23 -0400319some or all of the buffers from the page when it is being truncated. It
320returns zero on success. If ->invalidatepage is zero, the kernel uses
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321block_invalidatepage() instead.
322
323 ->releasepage() is called when the kernel is about to try to drop the
324buffers from the page in preparation for freeing it. It returns zero to
325indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
326the kernel assumes that the fs has no private interest in the buffers.
327
Linus Torvalds6072d132010-12-01 13:35:19 -0500328 ->freepage() is called when the kernel is done dropping the page
329from the page cache.
330
Trond Myklebuste3db7692007-01-10 23:15:39 -0800331 ->launder_page() may be called prior to releasing a page if
332it is still found to be dirty. It returns zero if the page was successfully
333cleaned, or an error value if not. Note that in order to prevent the page
334getting mapped back in and redirtied, it needs to be kept locked
335across the entire operation.
336
Mel Gorman62c230b2012-07-31 16:44:55 -0700337 ->swap_activate will be called with a non-zero argument on
338files backing (non block device backed) swapfiles. A return value
339of zero indicates success, in which case this file can be used for
340backing swapspace. The swapspace operations will be proxied to the
341address space operations.
342
343 ->swap_deactivate() will be called in the sys_swapoff()
344path after ->swap_activate() returned success.
345
Linus Torvalds1da177e2005-04-16 15:20:36 -0700346----------------------- file_lock_operations ------------------------------
347prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
349 void (*fl_release_private)(struct file_lock *);
350
351
352locking rules:
Jeff Layton1c8c6012013-06-21 08:58:15 -0400353 inode->i_lock may block
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100354fl_copy_lock: yes no
Jeff Layton2ece1732014-08-12 10:38:07 -0400355fl_release_private: maybe maybe[1]
356
357[1]: ->fl_release_private for flock or POSIX locks is currently allowed
358to block. Leases however can still be freed while the i_lock is held and
359so fl_release_private called on a lease should not block.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700360
361----------------------- lock_manager_operations ---------------------------
362prototypes:
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400363 int (*lm_compare_owner)(struct file_lock *, struct file_lock *);
Jeff Layton3999e492013-06-21 08:58:19 -0400364 unsigned long (*lm_owner_key)(struct file_lock *);
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400365 void (*lm_notify)(struct file_lock *); /* unblock callback */
366 int (*lm_grant)(struct file_lock *, struct file_lock *, int);
J. Bruce Fields8fb47a42011-07-20 20:21:59 -0400367 void (*lm_break)(struct file_lock *); /* break_lease callback */
368 int (*lm_change)(struct file_lock **, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700369
370locking rules:
Jeff Layton1c8c6012013-06-21 08:58:15 -0400371
Jeff Layton7b2296a2013-06-21 08:58:20 -0400372 inode->i_lock blocked_lock_lock may block
373lm_compare_owner: yes[1] maybe no
374lm_owner_key yes[1] yes no
375lm_notify: yes yes no
376lm_grant: no no no
377lm_break: yes no no
378lm_change yes no no
Jeff Layton1c8c6012013-06-21 08:58:15 -0400379
Jeff Layton3999e492013-06-21 08:58:19 -0400380[1]: ->lm_compare_owner and ->lm_owner_key are generally called with
381*an* inode->i_lock held. It may not be the i_lock of the inode
382associated with either file_lock argument! This is the case with deadlock
383detection, since the code has to chase down the owners of locks that may
384be entirely unrelated to the one on which the lock is being acquired.
Jeff Layton7b2296a2013-06-21 08:58:20 -0400385For deadlock detection however, the blocked_lock_lock is also held. The
Jeff Layton3999e492013-06-21 08:58:19 -0400386fact that these locks are held ensures that the file_locks do not
387disappear out from under you while doing the comparison or generating an
388owner key.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700389
Linus Torvalds1da177e2005-04-16 15:20:36 -0700390--------------------------- buffer_head -----------------------------------
391prototypes:
392 void (*b_end_io)(struct buffer_head *bh, int uptodate);
393
394locking rules:
395 called from interrupts. In other words, extreme care is needed here.
396bh is locked, but that's all warranties we have here. Currently only RAID1,
397highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
398call this method upon the IO completion.
399
400--------------------------- block_device_operations -----------------------
401prototypes:
Christoph Hellwige1455d12010-10-06 10:46:53 +0200402 int (*open) (struct block_device *, fmode_t);
403 int (*release) (struct gendisk *, fmode_t);
404 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
405 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
Dan Williams7a9eb202016-06-03 18:06:47 -0700406 int (*direct_access) (struct block_device *, sector_t, void **,
Ross Zwislere2e05392015-08-18 13:55:41 -0600407 unsigned long *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700408 int (*media_changed) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200409 void (*unlock_native_capacity) (struct gendisk *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700410 int (*revalidate_disk) (struct gendisk *);
Christoph Hellwige1455d12010-10-06 10:46:53 +0200411 int (*getgeo)(struct block_device *, struct hd_geometry *);
412 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700413
414locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100415 bd_mutex
416open: yes
417release: yes
418ioctl: no
419compat_ioctl: no
420direct_access: no
421media_changed: no
422unlock_native_capacity: no
423revalidate_disk: no
424getgeo: no
425swap_slot_free_notify: no (see below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700426
Christoph Hellwige1455d12010-10-06 10:46:53 +0200427media_changed, unlock_native_capacity and revalidate_disk are called only from
428check_disk_change().
429
430swap_slot_free_notify is called with swap_lock and sometimes the page lock
431held.
432
Linus Torvalds1da177e2005-04-16 15:20:36 -0700433
434--------------------------- file_operations -------------------------------
435prototypes:
436 loff_t (*llseek) (struct file *, loff_t, int);
437 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700438 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
Al Viro293bc982014-02-11 18:37:41 -0500439 ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
440 ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
Al Viro2233f312013-05-22 21:44:23 -0400441 int (*iterate) (struct file *, struct dir_context *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700442 unsigned int (*poll) (struct file *, struct poll_table_struct *);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700443 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
444 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
445 int (*mmap) (struct file *, struct vm_area_struct *);
446 int (*open) (struct inode *, struct file *);
447 int (*flush) (struct file *);
448 int (*release) (struct inode *, struct file *);
Josef Bacik02c24a82011-07-16 20:44:56 -0400449 int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700450 int (*fasync) (int, struct file *, int);
451 int (*lock) (struct file *, int, struct file_lock *);
452 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
453 loff_t *);
454 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
455 loff_t *);
456 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
457 void __user *);
458 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
459 loff_t *, int);
460 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
461 unsigned long, unsigned long, unsigned long);
462 int (*check_flags)(int);
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100463 int (*flock) (struct file *, int, struct file_lock *);
464 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
465 size_t, unsigned int);
466 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
467 size_t, unsigned int);
Jeff Laytone6f5c782014-08-22 10:40:25 -0400468 int (*setlease)(struct file *, long, struct file_lock **, void **);
Christoph Hellwig2fe17c12011-01-14 13:07:43 +0100469 long (*fallocate)(struct file *, int, loff_t, loff_t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700470};
471
472locking rules:
Jeff Laytonc45198e2014-09-01 07:12:07 -0400473 All may block.
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100474
Linus Torvalds1da177e2005-04-16 15:20:36 -0700475->llseek() locking has moved from llseek to the individual llseek
476implementations. If your fs is not using generic_file_llseek, you
477need to acquire and release the appropriate locks in your ->llseek().
478For many filesystems, it is probably safe to acquire the inode
Jan Blunck866707f2010-05-26 14:44:54 -0700479mutex or just to use i_size_read() instead.
480Note: this does not protect the file->f_pos against concurrent modifications
481since this is something the userspace has to take care about.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700482
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100483->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
484Most instances call fasync_helper(), which does that maintenance, so it's
485not normally something one needs to worry about. Return values > 0 will be
486mapped to zero in the VFS layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700487
488->readdir() and ->ioctl() on directories must be changed. Ideally we would
489move ->readdir() to inode_operations and use a separate method for directory
490->ioctl() or kill the latter completely. One of the problems is that for
491anything that resembles union-mount we won't have a struct file for all
492components. And there are other reasons why the current interface is a mess...
493
Linus Torvalds1da177e2005-04-16 15:20:36 -0700494->read on directories probably must go away - we should just enforce -EISDIR
495in sys_read() and friends.
496
Jeff Laytonf82b4b62014-08-22 18:50:48 -0400497->setlease operations should call generic_setlease() before or after setting
498the lease within the individual filesystem to record the result of the
499operation
500
Linus Torvalds1da177e2005-04-16 15:20:36 -0700501--------------------------- dquot_operations -------------------------------
502prototypes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700503 int (*write_dquot) (struct dquot *);
504 int (*acquire_dquot) (struct dquot *);
505 int (*release_dquot) (struct dquot *);
506 int (*mark_dirty) (struct dquot *);
507 int (*write_info) (struct super_block *, int);
508
509These operations are intended to be more or less wrapping functions that ensure
510a proper locking wrt the filesystem and call the generic quota operations.
511
512What filesystem should expect from the generic quota functions:
513
514 FS recursion Held locks when called
Linus Torvalds1da177e2005-04-16 15:20:36 -0700515write_dquot: yes dqonoff_sem or dqptr_sem
516acquire_dquot: yes dqonoff_sem or dqptr_sem
517release_dquot: yes dqonoff_sem or dqptr_sem
518mark_dirty: no -
519write_info: yes dqonoff_sem
520
521FS recursion means calling ->quota_read() and ->quota_write() from superblock
522operations.
523
Linus Torvalds1da177e2005-04-16 15:20:36 -0700524More details about quota locking can be found in fs/dquot.c.
525
526--------------------------- vm_operations_struct -----------------------------
527prototypes:
528 void (*open)(struct vm_area_struct*);
529 void (*close)(struct vm_area_struct*);
Nick Piggind0217ac2007-07-19 01:47:03 -0700530 int (*fault)(struct vm_area_struct*, struct vm_fault *);
Nick Pigginc2ec1752009-03-31 15:23:21 -0700531 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
Boaz Harroshdd906182015-04-15 16:15:11 -0700532 int (*pfn_mkwrite)(struct vm_area_struct *, struct vm_fault *);
Rik van Riel28b2ee22008-07-23 21:27:05 -0700533 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700534
535locking rules:
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100536 mmap_sem PageLocked(page)
537open: yes
538close: yes
539fault: yes can return with page locked
Kirill A. Shutemov8c6e50b2014-04-07 15:37:18 -0700540map_pages: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100541page_mkwrite: yes can return with page locked
Boaz Harroshdd906182015-04-15 16:15:11 -0700542pfn_mkwrite: yes
Christoph Hellwigb83be6f2010-12-16 12:04:54 +0100543access: yes
Mark Fashehed2f2f92007-07-19 01:47:01 -0700544
Nick Pigginb827e492009-04-30 15:08:16 -0700545 ->fault() is called when a previously not present pte is about
546to be faulted in. The filesystem must find and return the page associated
547with the passed in "pgoff" in the vm_fault structure. If it is possible that
548the page may be truncated and/or invalidated, then the filesystem must lock
549the page, then ensure it is not already truncated (the page lock will block
550subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
551locked. The VM will unlock the page.
552
Kirill A. Shutemov8c6e50b2014-04-07 15:37:18 -0700553 ->map_pages() is called when VM asks to map easy accessible pages.
Kirill A. Shutemovbae473a2016-07-26 15:25:20 -0700554Filesystem should find and map pages associated with offsets from "start_pgoff"
555till "end_pgoff". ->map_pages() is called with page table locked and must
Kirill A. Shutemov8c6e50b2014-04-07 15:37:18 -0700556not block. If it's not possible to reach a page without blocking,
557filesystem should skip it. Filesystem should use do_set_pte() to setup
Kirill A. Shutemovbae473a2016-07-26 15:25:20 -0700558page table entry. Pointer to entry associated with the page is passed in
559"pte" field in fault_env structure. Pointers to entries for other offsets
560should be calculated relative to "pte".
Kirill A. Shutemov8c6e50b2014-04-07 15:37:18 -0700561
Nick Pigginb827e492009-04-30 15:08:16 -0700562 ->page_mkwrite() is called when a previously read-only pte is
563about to become writeable. The filesystem again must ensure that there are
564no truncate/invalidate races, and then return with the page locked. If
565the page has been truncated, the filesystem should not look up a new page
566like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
567will cause the VM to retry the fault.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700568
Boaz Harroshdd906182015-04-15 16:15:11 -0700569 ->pfn_mkwrite() is the same as page_mkwrite but when the pte is
570VM_PFNMAP or VM_MIXEDMAP with a page-less entry. Expected return is
571VM_FAULT_NOPAGE. Or one of the VM_FAULT_ERROR types. The default behavior
572after this call is to make the pte read-write, unless pfn_mkwrite returns
573an error.
574
Rik van Riel28b2ee22008-07-23 21:27:05 -0700575 ->access() is called when get_user_pages() fails in
Stefan Weil507da6a2013-12-05 20:34:05 +0100576access_process_vm(), typically used to debug a process through
Rik van Riel28b2ee22008-07-23 21:27:05 -0700577/proc/pid/mem or ptrace. This function is needed only for
578VM_IO | VM_PFNMAP VMAs.
579
Linus Torvalds1da177e2005-04-16 15:20:36 -0700580================================================================================
581 Dubious stuff
582
583(if you break something or notice that it is broken and do not fix it yourself
584- at least put it here)