| 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 *, unsigned int); |
| 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, bool); |
| struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int); |
| 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); |
| int (*atomic_open)(struct inode *, struct dentry *, |
| struct file *, unsigned open_flag, |
| umode_t create_mode, int *opened); |
| int (*dentry_open)(struct dentry *, struct file *, const struct cred *); |
| |
| 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 |
| 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 |
| atomic_open: yes |
| dentry_open: no |
| |
| Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on |
| victim. |
| cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem. |
| |
| 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 *); |
| 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 |
| sync_fs: read |
| freeze_fs: write |
| unfreeze_fs: write |
| 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 *); |
| int (*swap_activate)(struct file *); |
| int (*swap_deactivate)(struct file *); |
| |
| 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 |
| swap_activate: no |
| swap_deactivate: no |
| |
| ->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. |
| |
| ->swap_activate will be called with a non-zero argument on |
| files backing (non block device backed) swapfiles. A return value |
| of zero indicates success, in which case this file can be used for |
| backing swapspace. The swapspace operations will be proxied to the |
| address space operations. |
| |
| ->swap_deactivate() will be called in the sys_swapoff() |
| path after ->swap_activate() returned success. |
| |
| ----------------------- 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_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_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) |