The text below describes the locking rules for VFS-related methods.It is (believed to be) up-to-date. *Please*, if you change anything inprototypes or locking protocols - update this file. And update the relevantinstances 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 tobe 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-walkd_revalidate: no no yes (ref-walk) maybed_hash no no no maybed_compare: yes no no maybed_delete: no yes no nod_release: no no yes nod_prune: no yes no nod_iput: no no yes nod_dname: no no no nod_automount: no no yes nod_manage: no no yes (ref-walk) maybe --------------------------- inode_operations --------------------------- prototypes: int (*create) (struct inode *,struct dentry *,umode_t, struct nameidata *); struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameidata *); 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 *,umode_t); int (*rmdir) (struct inode *,struct dentry *); int (*mknod) (struct inode *,struct dentry *,umode_t,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 *); int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len); void (*update_time)(struct inode *, struct timespec *, int); locking rules: all may block i_mutex(inode)lookup: yescreate: yeslink: yes (both)mknod: yessymlink: yesmkdir: yesunlink: yes (both)rmdir: yes (both) (see below)rename: yes (all) (see below)readlink: nofollow_link: noput_link: notruncate: yes (see below)setattr: yespermission: no (may not block if called in rcu-walk mode)get_acl: nogetattr: nosetxattr: yesgetxattr: nolistxattr: noremovexattr: yesfiemap: noupdate_time: no Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex onvictim. cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem. ->truncate() is never called directly - it's a callback, not amethod. It's called by vmtruncate() - deprecated library function used by->setattr(). Locking information above applies to that call (i.e. isinherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had beenpassed). See Documentation/filesystems/directory-locking for more detailed discussionof 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 dentry *); 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_umountalloc_inode:destroy_inode:dirty_inode:write_inode:drop_inode: !!!inode->i_lock!!!evict_inode:put_super: writewrite_super: readsync_fs: readfreeze_fs: readunfreeze_fs: readstatfs: maybe(read) (see below)remount_fs: writeumount_begin: noshow_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 orcompat), but that's an accident of bad API; s_umount is used to pinthe superblock down when we only have dev_t given us by userland toidentify the superblock. Everything else (statfs(), fstatfs(), etc.)doesn't hold it when calling ->statfs() - superblock is pinned downby resolving the pathname passed to syscall.->quota_read() and ->quota_write() functions are both guaranteed tobe the only ones operating on the quota file by the quota code (viadqio_sem) (unless an admin really wants to screw up something andwrites to quota files with quotas on). For other details about lockingsee also dquot_operations section.->bdev_try_to_free_page is called from the ->releasepage handler ofthe 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 blockmount yeskill_sb yes ->mount() returns ERR_PTR or the root dentry; its superblock should be lockedon 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_mutexwritepage: yes, unlocks (see below)readpage: yes, unlockssync_page: maybewritepages:set_page_dirty noreadpages:write_begin: locks the page yeswrite_end: yes, unlocks yesbmap:invalidatepage: yesreleasepage: yesfreepage: yesdirect_IO:get_xip_mem: maybemigratepage: yes (both)launder_page: yesis_partially_uptodate: yeserror_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/Ocompletion. ->readpages() populates the pagecache with the passed pages and startsI/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 differdepending upon the mode. If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) thenit *must* start I/O against the page, even if that would involveblocking 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 aspossible. So writepage should try to avoid blocking againstcurrently-in-progress I/O. If the filesystem is not called for "sync" and it determines that itwould need to block against in-progress I/O to be able to start new I/Oagainst the page the filesystem should redirty the page withredirty_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 anyin-progress I/O and then start new I/O. The filesystem should unlock the page synchronously, before returning to thecaller, unless ->writepage() returns special WRITEPAGE_ACTIVATEvalue. WRITEPAGE_ACTIVATE means that page cannot really be written outcurrently, and VM should stop calling ->writepage() on this page for sometime. VM does this by moving page to the head of the active list, hence thename. Unless the filesystem is going to redirty_page_for_writepage(), unlock the pageand return zero, writepage *must* run set_page_writeback() against the page,followed by unlocking it. Once set_page_writeback() has been run against thepage, write I/O can be submitted and the write I/O completion handler must runend_page_writeback() once the I/O is complete. If no I/O is submitted, thefilesystem must run end_page_writeback() against the page before returning fromwritepage. 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 toset_page_writeback() and end_page_writeback(). Note, failure to run either redirty_page_for_writepage() or the combination ofset_page_writeback()/end_page_writeback() on a page submitted to writepagewill leave the page itself marked clean but it will be tagged as dirty in theradix tree. This incoherency can lead to all sorts of hard-to-debug problemsin the filesystem like having dirty inodes at umount and losing written data. ->sync_page() locking rules are not well-defined - usually it is calledwith lock on page, but that is not guaranteed. Considering the currentlyexisting instances of this method ->sync_page() itself doesn't lookwell-defined... ->writepages() is used for periodic writeback and for syscall-initiatedsync 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 iswritten. The address_space implementation may write more (or less) pagesthan *nr_to_write asks for, but it should try to be reasonably close. Ifnr_to_write is NULL, all dirty pages must be written. writepages should _only_ write pages which are present onmapping->io_pages. ->set_page_dirty() is called from various places in the kernelwhen the target page is marked as needing writeback. It may be calledunder spinlock (it cannot block) and is sometimes called with the pagenot locked. ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by somefilesystems 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 dropsome or all of the buffers from the page when it is being truncated. Itreturns zero on success. If ->invalidatepage is zero, the kernel usesblock_invalidatepage() instead. ->releasepage() is called when the kernel is about to try to drop thebuffers from the page in preparation for freeing it. It returns zero toindicate 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 pagefrom the page cache. ->launder_page() may be called prior to releasing a page ifit is still found to be dirty. It returns zero if the page was successfullycleaned, or an error value if not. Note that in order to prevent the pagegetting mapped back in and redirtied, it needs to be kept lockedacross 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 blockfl_copy_lock: yes nofl_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 blocklm_compare_owner: yes nolm_notify: yes nolm_grant: no nolm_release_private: maybe nolm_break: yes nolm_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 devicescall 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_mutexopen: yesrelease: yesioctl: nocompat_ioctl: nodirect_access: nomedia_changed: nounlock_native_capacity: norevalidate_disk: nogetgeo: noswap_slot_free_notify: no (see below) media_changed, unlock_native_capacity and revalidate_disk are called only fromcheck_disk_change(). swap_slot_free_notify is called with swap_lock and sometimes the page lockheld. --------------------------- 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 llseekimplementations. If your fs is not using generic_file_llseek, youneed to acquire and release the appropriate locks in your ->llseek().For many filesystems, it is probably safe to acquire the inodemutex or just to use i_size_read() instead.Note: this does not protect the file->f_pos against concurrent modificationssince 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'snot normally something one needs to worry about. Return values > 0 will bemapped to zero in the VFS layer. ->readdir() and ->ioctl() on directories must be changed. Ideally we wouldmove ->readdir() to inode_operations and use a separate method for directory->ioctl() or kill the latter completely. One of the problems is that foranything that resembles union-mount we won't have a struct file for allcomponents. And there are other reasons why the current interface is a mess... ->read on directories probably must go away - we should just enforce -EISDIRin 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 ensurea 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 calledwrite_dquot: yes dqonoff_sem or dqptr_semacquire_dquot: yes dqonoff_sem or dqptr_semrelease_dquot: yes dqonoff_sem or dqptr_semmark_dirty: no -write_info: yes dqonoff_sem FS recursion means calling ->quota_read() and ->quota_write() from superblockoperations. 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);Lines 1–500 of 534. Load more
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 *,umode_t, 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 *,umode_t); int (*rmdir) (struct inode *,struct dentry *); int (*mknod) (struct inode *,struct dentry *,umode_t,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 *); int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len); void (*update_time)(struct inode *, struct timespec *, int); 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 fiemap: no update_time: 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 dentry *); 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);