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Based on kernel version 3.2. Page generated on 2012-01-05 23:28 EST.

		The text below describes the locking rules for VFS-related methods.
	It is (believed to be) up-to-date. *Please*, if you change anything in
	prototypes or locking protocols - update this file. And update the relevant
	instances in the tree, don't leave that to maintainers of filesystems/devices/
	etc. At the very least, put the list of dubious cases in the end of this file.
	Don't turn it into log - maintainers of out-of-the-tree code are supposed to
	be able to use diff(1).
		Thing currently missing here: socket operations. Alexey?
	
	--------------------------- dentry_operations --------------------------
	prototypes:
		int (*d_revalidate)(struct dentry *, struct nameidata *);
		int (*d_hash)(const struct dentry *, const struct inode *,
				struct qstr *);
		int (*d_compare)(const struct dentry *, const struct inode *,
				const struct dentry *, const struct inode *,
				unsigned int, const char *, const struct qstr *);
		int (*d_delete)(struct dentry *);
		void (*d_release)(struct dentry *);
		void (*d_iput)(struct dentry *, struct inode *);
		char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
		struct vfsmount *(*d_automount)(struct path *path);
		int (*d_manage)(struct dentry *, bool);
	
	locking rules:
			rename_lock	->d_lock	may block	rcu-walk
	d_revalidate:	no		no		yes (ref-walk)	maybe
	d_hash		no		no		no		maybe
	d_compare:	yes		no		no		maybe
	d_delete:	no		yes		no		no
	d_release:	no		no		yes		no
	d_prune:        no              yes             no              no
	d_iput:		no		no		yes		no
	d_dname:	no		no		no		no
	d_automount:	no		no		yes		no
	d_manage:	no		no		yes (ref-walk)	maybe
	
	--------------------------- inode_operations --------------------------- 
	prototypes:
		int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
		struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
	ata *);
		int (*link) (struct dentry *,struct inode *,struct dentry *);
		int (*unlink) (struct inode *,struct dentry *);
		int (*symlink) (struct inode *,struct dentry *,const char *);
		int (*mkdir) (struct inode *,struct dentry *,int);
		int (*rmdir) (struct inode *,struct dentry *);
		int (*mknod) (struct inode *,struct dentry *,int,dev_t);
		int (*rename) (struct inode *, struct dentry *,
				struct inode *, struct dentry *);
		int (*readlink) (struct dentry *, char __user *,int);
		void * (*follow_link) (struct dentry *, struct nameidata *);
		void (*put_link) (struct dentry *, struct nameidata *, void *);
		void (*truncate) (struct inode *);
		int (*permission) (struct inode *, int, unsigned int);
		int (*get_acl)(struct inode *, int);
		int (*setattr) (struct dentry *, struct iattr *);
		int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
		int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
		ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
		ssize_t (*listxattr) (struct dentry *, char *, size_t);
		int (*removexattr) (struct dentry *, const char *);
		void (*truncate_range)(struct inode *, loff_t, loff_t);
		int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
	
	locking rules:
		all may block
			i_mutex(inode)
	lookup:		yes
	create:		yes
	link:		yes (both)
	mknod:		yes
	symlink:	yes
	mkdir:		yes
	unlink:		yes (both)
	rmdir:		yes (both)	(see below)
	rename:		yes (all)	(see below)
	readlink:	no
	follow_link:	no
	put_link:	no
	truncate:	yes		(see below)
	setattr:	yes
	permission:	no (may not block if called in rcu-walk mode)
	get_acl:	no
	getattr:	no
	setxattr:	yes
	getxattr:	no
	listxattr:	no
	removexattr:	yes
	truncate_range:	yes
	fiemap:		no
		Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
	victim.
		cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
		->truncate() is never called directly - it's a callback, not a
	method. It's called by vmtruncate() - deprecated library function used by
	->setattr(). Locking information above applies to that call (i.e. is
	inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
	passed).
	
	See Documentation/filesystems/directory-locking for more detailed discussion
	of the locking scheme for directory operations.
	
	--------------------------- super_operations ---------------------------
	prototypes:
		struct inode *(*alloc_inode)(struct super_block *sb);
		void (*destroy_inode)(struct inode *);
		void (*dirty_inode) (struct inode *, int flags);
		int (*write_inode) (struct inode *, struct writeback_control *wbc);
		int (*drop_inode) (struct inode *);
		void (*evict_inode) (struct inode *);
		void (*put_super) (struct super_block *);
		void (*write_super) (struct super_block *);
		int (*sync_fs)(struct super_block *sb, int wait);
		int (*freeze_fs) (struct super_block *);
		int (*unfreeze_fs) (struct super_block *);
		int (*statfs) (struct dentry *, struct kstatfs *);
		int (*remount_fs) (struct super_block *, int *, char *);
		void (*umount_begin) (struct super_block *);
		int (*show_options)(struct seq_file *, struct vfsmount *);
		ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
		ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
		int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
	
	locking rules:
		All may block [not true, see below]
				s_umount
	alloc_inode:
	destroy_inode:
	dirty_inode:
	write_inode:
	drop_inode:				!!!inode->i_lock!!!
	evict_inode:
	put_super:		write
	write_super:		read
	sync_fs:		read
	freeze_fs:		read
	unfreeze_fs:		read
	statfs:			maybe(read)	(see below)
	remount_fs:		write
	umount_begin:		no
	show_options:		no		(namespace_sem)
	quota_read:		no		(see below)
	quota_write:		no		(see below)
	bdev_try_to_free_page:	no		(see below)
	
	->statfs() has s_umount (shared) when called by ustat(2) (native or
	compat), but that's an accident of bad API; s_umount is used to pin
	the superblock down when we only have dev_t given us by userland to
	identify the superblock.  Everything else (statfs(), fstatfs(), etc.)
	doesn't hold it when calling ->statfs() - superblock is pinned down
	by resolving the pathname passed to syscall.
	->quota_read() and ->quota_write() functions are both guaranteed to
	be the only ones operating on the quota file by the quota code (via
	dqio_sem) (unless an admin really wants to screw up something and
	writes to quota files with quotas on). For other details about locking
	see also dquot_operations section.
	->bdev_try_to_free_page is called from the ->releasepage handler of
	the block device inode.  See there for more details.
	
	--------------------------- file_system_type ---------------------------
	prototypes:
		int (*get_sb) (struct file_system_type *, int,
			       const char *, void *, struct vfsmount *);
		struct dentry *(*mount) (struct file_system_type *, int,
			       const char *, void *);
		void (*kill_sb) (struct super_block *);
	locking rules:
			may block
	mount		yes
	kill_sb		yes
	
	->mount() returns ERR_PTR or the root dentry; its superblock should be locked
	on return.
	->kill_sb() takes a write-locked superblock, does all shutdown work on it,
	unlocks and drops the reference.
	
	--------------------------- address_space_operations --------------------------
	prototypes:
		int (*writepage)(struct page *page, struct writeback_control *wbc);
		int (*readpage)(struct file *, struct page *);
		int (*sync_page)(struct page *);
		int (*writepages)(struct address_space *, struct writeback_control *);
		int (*set_page_dirty)(struct page *page);
		int (*readpages)(struct file *filp, struct address_space *mapping,
				struct list_head *pages, unsigned nr_pages);
		int (*write_begin)(struct file *, struct address_space *mapping,
					loff_t pos, unsigned len, unsigned flags,
					struct page **pagep, void **fsdata);
		int (*write_end)(struct file *, struct address_space *mapping,
					loff_t pos, unsigned len, unsigned copied,
					struct page *page, void *fsdata);
		sector_t (*bmap)(struct address_space *, sector_t);
		int (*invalidatepage) (struct page *, unsigned long);
		int (*releasepage) (struct page *, int);
		void (*freepage)(struct page *);
		int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
				loff_t offset, unsigned long nr_segs);
		int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
					unsigned long *);
		int (*migratepage)(struct address_space *, struct page *, struct page *);
		int (*launder_page)(struct page *);
		int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
		int (*error_remove_page)(struct address_space *, struct page *);
	
	locking rules:
		All except set_page_dirty and freepage may block
	
				PageLocked(page)	i_mutex
	writepage:		yes, unlocks (see below)
	readpage:		yes, unlocks
	sync_page:		maybe
	writepages:
	set_page_dirty		no
	readpages:
	write_begin:		locks the page		yes
	write_end:		yes, unlocks		yes
	bmap:
	invalidatepage:		yes
	releasepage:		yes
	freepage:		yes
	direct_IO:
	get_xip_mem:					maybe
	migratepage:		yes (both)
	launder_page:		yes
	is_partially_uptodate:	yes
	error_remove_page:	yes
	
		->write_begin(), ->write_end(), ->sync_page() and ->readpage()
	may be called from the request handler (/dev/loop).
	
		->readpage() unlocks the page, either synchronously or via I/O
	completion.
	
		->readpages() populates the pagecache with the passed pages and starts
	I/O against them.  They come unlocked upon I/O completion.
	
		->writepage() is used for two purposes: for "memory cleansing" and for
	"sync".  These are quite different operations and the behaviour may differ
	depending upon the mode.
	
	If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
	it *must* start I/O against the page, even if that would involve
	blocking on in-progress I/O.
	
	If writepage is called for memory cleansing (sync_mode ==
	WBC_SYNC_NONE) then its role is to get as much writeout underway as
	possible.  So writepage should try to avoid blocking against
	currently-in-progress I/O.
	
	If the filesystem is not called for "sync" and it determines that it
	would need to block against in-progress I/O to be able to start new I/O
	against the page the filesystem should redirty the page with
	redirty_page_for_writepage(), then unlock the page and return zero.
	This may also be done to avoid internal deadlocks, but rarely.
	
	If the filesystem is called for sync then it must wait on any
	in-progress I/O and then start new I/O.
	
	The filesystem should unlock the page synchronously, before returning to the
	caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
	value. WRITEPAGE_ACTIVATE means that page cannot really be written out
	currently, and VM should stop calling ->writepage() on this page for some
	time. VM does this by moving page to the head of the active list, hence the
	name.
	
	Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
	and return zero, writepage *must* run set_page_writeback() against the page,
	followed by unlocking it.  Once set_page_writeback() has been run against the
	page, write I/O can be submitted and the write I/O completion handler must run
	end_page_writeback() once the I/O is complete.  If no I/O is submitted, the
	filesystem must run end_page_writeback() against the page before returning from
	writepage.
	
	That is: after 2.5.12, pages which are under writeout are *not* locked.  Note,
	if the filesystem needs the page to be locked during writeout, that is ok, too,
	the page is allowed to be unlocked at any point in time between the calls to
	set_page_writeback() and end_page_writeback().
	
	Note, failure to run either redirty_page_for_writepage() or the combination of
	set_page_writeback()/end_page_writeback() on a page submitted to writepage
	will leave the page itself marked clean but it will be tagged as dirty in the
	radix tree.  This incoherency can lead to all sorts of hard-to-debug problems
	in the filesystem like having dirty inodes at umount and losing written data.
	
		->sync_page() locking rules are not well-defined - usually it is called
	with lock on page, but that is not guaranteed. Considering the currently
	existing instances of this method ->sync_page() itself doesn't look
	well-defined...
	
		->writepages() is used for periodic writeback and for syscall-initiated
	sync operations.  The address_space should start I/O against at least
	*nr_to_write pages.  *nr_to_write must be decremented for each page which is
	written.  The address_space implementation may write more (or less) pages
	than *nr_to_write asks for, but it should try to be reasonably close.  If
	nr_to_write is NULL, all dirty pages must be written.
	
	writepages should _only_ write pages which are present on
	mapping->io_pages.
	
		->set_page_dirty() is called from various places in the kernel
	when the target page is marked as needing writeback.  It may be called
	under spinlock (it cannot block) and is sometimes called with the page
	not locked.
	
		->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
	filesystems and by the swapper. The latter will eventually go away.  Please,
	keep it that way and don't breed new callers.
	
		->invalidatepage() is called when the filesystem must attempt to drop
	some or all of the buffers from the page when it is being truncated.  It
	returns zero on success.  If ->invalidatepage is zero, the kernel uses
	block_invalidatepage() instead.
	
		->releasepage() is called when the kernel is about to try to drop the
	buffers from the page in preparation for freeing it.  It returns zero to
	indicate that the buffers are (or may be) freeable.  If ->releasepage is zero,
	the kernel assumes that the fs has no private interest in the buffers.
	
		->freepage() is called when the kernel is done dropping the page
	from the page cache.
	
		->launder_page() may be called prior to releasing a page if
	it is still found to be dirty. It returns zero if the page was successfully
	cleaned, or an error value if not. Note that in order to prevent the page
	getting mapped back in and redirtied, it needs to be kept locked
	across the entire operation.
	
	----------------------- file_lock_operations ------------------------------
	prototypes:
		void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
		void (*fl_release_private)(struct file_lock *);
	
	
	locking rules:
				file_lock_lock	may block
	fl_copy_lock:		yes		no
	fl_release_private:	maybe		no
	
	----------------------- lock_manager_operations ---------------------------
	prototypes:
		int (*lm_compare_owner)(struct file_lock *, struct file_lock *);
		void (*lm_notify)(struct file_lock *);  /* unblock callback */
		int (*lm_grant)(struct file_lock *, struct file_lock *, int);
		void (*lm_release_private)(struct file_lock *);
		void (*lm_break)(struct file_lock *); /* break_lease callback */
		int (*lm_change)(struct file_lock **, int);
	
	locking rules:
				file_lock_lock	may block
	lm_compare_owner:	yes		no
	lm_notify:		yes		no
	lm_grant:		no		no
	lm_release_private:	maybe		no
	lm_break:		yes		no
	lm_change		yes		no
	
	--------------------------- buffer_head -----------------------------------
	prototypes:
		void (*b_end_io)(struct buffer_head *bh, int uptodate);
	
	locking rules:
		called from interrupts. In other words, extreme care is needed here.
	bh is locked, but that's all warranties we have here. Currently only RAID1,
	highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
	call this method upon the IO completion.
	
	--------------------------- block_device_operations -----------------------
	prototypes:
		int (*open) (struct block_device *, fmode_t);
		int (*release) (struct gendisk *, fmode_t);
		int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
		int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
		int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
		int (*media_changed) (struct gendisk *);
		void (*unlock_native_capacity) (struct gendisk *);
		int (*revalidate_disk) (struct gendisk *);
		int (*getgeo)(struct block_device *, struct hd_geometry *);
		void (*swap_slot_free_notify) (struct block_device *, unsigned long);
	
	locking rules:
				bd_mutex
	open:			yes
	release:		yes
	ioctl:			no
	compat_ioctl:		no
	direct_access:		no
	media_changed:		no
	unlock_native_capacity:	no
	revalidate_disk:	no
	getgeo:			no
	swap_slot_free_notify:	no	(see below)
	
	media_changed, unlock_native_capacity and revalidate_disk are called only from
	check_disk_change().
	
	swap_slot_free_notify is called with swap_lock and sometimes the page lock
	held.
	
	
	--------------------------- file_operations -------------------------------
	prototypes:
		loff_t (*llseek) (struct file *, loff_t, int);
		ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
		ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
		ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
		ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
		int (*readdir) (struct file *, void *, filldir_t);
		unsigned int (*poll) (struct file *, struct poll_table_struct *);
		long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
		long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
		int (*mmap) (struct file *, struct vm_area_struct *);
		int (*open) (struct inode *, struct file *);
		int (*flush) (struct file *);
		int (*release) (struct inode *, struct file *);
		int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
		int (*aio_fsync) (struct kiocb *, int datasync);
		int (*fasync) (int, struct file *, int);
		int (*lock) (struct file *, int, struct file_lock *);
		ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
				loff_t *);
		ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
				loff_t *);
		ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
				void __user *);
		ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
				loff_t *, int);
		unsigned long (*get_unmapped_area)(struct file *, unsigned long,
				unsigned long, unsigned long, unsigned long);
		int (*check_flags)(int);
		int (*flock) (struct file *, int, struct file_lock *);
		ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
				size_t, unsigned int);
		ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
				size_t, unsigned int);
		int (*setlease)(struct file *, long, struct file_lock **);
		long (*fallocate)(struct file *, int, loff_t, loff_t);
	};
	
	locking rules:
		All may block except for ->setlease.
		No VFS locks held on entry except for ->setlease.
	
	->setlease has the file_list_lock held and must not sleep.
	
	->llseek() locking has moved from llseek to the individual llseek
	implementations.  If your fs is not using generic_file_llseek, you
	need to acquire and release the appropriate locks in your ->llseek().
	For many filesystems, it is probably safe to acquire the inode
	mutex or just to use i_size_read() instead.
	Note: this does not protect the file->f_pos against concurrent modifications
	since this is something the userspace has to take care about.
	
	->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
	Most instances call fasync_helper(), which does that maintenance, so it's
	not normally something one needs to worry about.  Return values > 0 will be
	mapped to zero in the VFS layer.
	
	->readdir() and ->ioctl() on directories must be changed. Ideally we would
	move ->readdir() to inode_operations and use a separate method for directory
	->ioctl() or kill the latter completely. One of the problems is that for
	anything that resembles union-mount we won't have a struct file for all
	components. And there are other reasons why the current interface is a mess...
	
	->read on directories probably must go away - we should just enforce -EISDIR
	in sys_read() and friends.
	
	--------------------------- dquot_operations -------------------------------
	prototypes:
		int (*write_dquot) (struct dquot *);
		int (*acquire_dquot) (struct dquot *);
		int (*release_dquot) (struct dquot *);
		int (*mark_dirty) (struct dquot *);
		int (*write_info) (struct super_block *, int);
	
	These operations are intended to be more or less wrapping functions that ensure
	a proper locking wrt the filesystem and call the generic quota operations.
	
	What filesystem should expect from the generic quota functions:
	
			FS recursion	Held locks when called
	write_dquot:	yes		dqonoff_sem or dqptr_sem
	acquire_dquot:	yes		dqonoff_sem or dqptr_sem
	release_dquot:	yes		dqonoff_sem or dqptr_sem
	mark_dirty:	no		-
	write_info:	yes		dqonoff_sem
	
	FS recursion means calling ->quota_read() and ->quota_write() from superblock
	operations.
	
	More details about quota locking can be found in fs/dquot.c.
	
	--------------------------- vm_operations_struct -----------------------------
	prototypes:
		void (*open)(struct vm_area_struct*);
		void (*close)(struct vm_area_struct*);
		int (*fault)(struct vm_area_struct*, struct vm_fault *);
		int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
		int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
	
	locking rules:
			mmap_sem	PageLocked(page)
	open:		yes
	close:		yes
	fault:		yes		can return with page locked
	page_mkwrite:	yes		can return with page locked
	access:		yes
	
		->fault() is called when a previously not present pte is about
	to be faulted in. The filesystem must find and return the page associated
	with the passed in "pgoff" in the vm_fault structure. If it is possible that
	the page may be truncated and/or invalidated, then the filesystem must lock
	the page, then ensure it is not already truncated (the page lock will block
	subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
	locked. The VM will unlock the page.
	
		->page_mkwrite() is called when a previously read-only pte is
	about to become writeable. The filesystem again must ensure that there are
	no truncate/invalidate races, and then return with the page locked. If
	the page has been truncated, the filesystem should not look up a new page
	like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
	will cause the VM to retry the fault.
	
		->access() is called when get_user_pages() fails in
	acces_process_vm(), typically used to debug a process through
	/proc/pid/mem or ptrace.  This function is needed only for
	VM_IO | VM_PFNMAP VMAs.
	
	================================================================================
				Dubious stuff
	
	(if you break something or notice that it is broken and do not fix it yourself
	- at least put it here)

• [ filesystems ]
• 00-INDEX
• 9p.txt
• adfs.txt
• affs.txt
• afs.txt
• autofs4-mount-control.txt
• automount-support.txt
• befs.txt
• bfs.txt
• btrfs.txt
• [ caching ]
• ceph.txt
• cifs.txt
• coda.txt
• [ configfs ]
• cramfs.txt
• debugfs.txt
• devpts.txt
• directory-locking
• dlmfs.txt
• dnotify.txt
• dnotify_test.c
• ecryptfs.txt
• exofs.txt
• ext2.txt
• ext3.txt
• ext4.txt
• fiemap.txt
• files.txt
• fuse.txt
• gfs2-glocks.txt
• gfs2-uevents.txt
• gfs2.txt
• hfs.txt
• hfsplus.txt
• hpfs.txt
• inotify.txt
• isofs.txt
• jfs.txt
• Locking
• locks.txt
• logfs.txt
• Makefile
• mandatory-locking.txt
• ncpfs.txt
• [ nfs ]
• nilfs2.txt
• ntfs.txt
• ocfs2.txt
• omfs.txt
• path-lookup.txt
• [ pohmelfs ]
• porting
• proc.txt
• quota.txt
• ramfs-rootfs-initramfs.txt
• relay.txt
• romfs.txt
• seq_file.txt
• sharedsubtree.txt
• spufs.txt
• squashfs.txt
• sysfs-pci.txt
• sysfs-tagging.txt
• sysfs.txt
• sysv-fs.txt
• tmpfs.txt
• ubifs.txt
• udf.txt
• ufs.txt
• vfat.txt
• vfs.txt
• xfs-delayed-logging-design.txt
• xfs.txt
• xip.txt
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