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Diffstat (limited to 'Documentation/filesystems/inotify.txt')
| -rw-r--r-- | Documentation/filesystems/inotify.txt | 197 |
1 files changed, 3 insertions, 194 deletions
diff --git a/Documentation/filesystems/inotify.txt b/Documentation/filesystems/inotify.txt index cfd02712b83e..51f61db787fb 100644 --- a/Documentation/filesystems/inotify.txt +++ b/Documentation/filesystems/inotify.txt @@ -4,201 +4,10 @@ Document started 15 Mar 2005 by Robert Love <rml@novell.com> +Document updated 4 Jan 2015 by Zhang Zhen <zhenzhang.zhang@huawei.com> + --Deleted obsoleted interface, just refer to manpages for user interface. - -(i) User Interface - -Inotify is controlled by a set of three system calls and normal file I/O on a -returned file descriptor. - -First step in using inotify is to initialise an inotify instance: - - int fd = inotify_init (); - -Each instance is associated with a unique, ordered queue. - -Change events are managed by "watches". A watch is an (object,mask) pair where -the object is a file or directory and the mask is a bit mask of one or more -inotify events that the application wishes to receive. See <linux/inotify.h> -for valid events. A watch is referenced by a watch descriptor, or wd. - -Watches are added via a path to the file. - -Watches on a directory will return events on any files inside of the directory. - -Adding a watch is simple: - - int wd = inotify_add_watch (fd, path, mask); - -Where "fd" is the return value from inotify_init(), path is the path to the -object to watch, and mask is the watch mask (see <linux/inotify.h>). - -You can update an existing watch in the same manner, by passing in a new mask. - -An existing watch is removed via - - int ret = inotify_rm_watch (fd, wd); - -Events are provided in the form of an inotify_event structure that is read(2) -from a given inotify instance. The filename is of dynamic length and follows -the struct. It is of size len. The filename is padded with null bytes to -ensure proper alignment. This padding is reflected in len. - -You can slurp multiple events by passing a large buffer, for example - - size_t len = read (fd, buf, BUF_LEN); - -Where "buf" is a pointer to an array of "inotify_event" structures at least -BUF_LEN bytes in size. The above example will return as many events as are -available and fit in BUF_LEN. - -Each inotify instance fd is also select()- and poll()-able. - -You can find the size of the current event queue via the standard FIONREAD -ioctl on the fd returned by inotify_init(). - -All watches are destroyed and cleaned up on close. - - -(ii) - -Prototypes: - - int inotify_init (void); - int inotify_add_watch (int fd, const char *path, __u32 mask); - int inotify_rm_watch (int fd, __u32 mask); - - -(iii) Kernel Interface - -Inotify's kernel API consists a set of functions for managing watches and an -event callback. - -To use the kernel API, you must first initialize an inotify instance with a set -of inotify_operations. You are given an opaque inotify_handle, which you use -for any further calls to inotify. - - struct inotify_handle *ih = inotify_init(my_event_handler); - -You must provide a function for processing events and a function for destroying -the inotify watch. - - void handle_event(struct inotify_watch *watch, u32 wd, u32 mask, - u32 cookie, const char *name, struct inode *inode) - - watch - the pointer to the inotify_watch that triggered this call - wd - the watch descriptor - mask - describes the event that occurred - cookie - an identifier for synchronizing events - name - the dentry name for affected files in a directory-based event - inode - the affected inode in a directory-based event - - void destroy_watch(struct inotify_watch *watch) - -You may add watches by providing a pre-allocated and initialized inotify_watch -structure and specifying the inode to watch along with an inotify event mask. -You must pin the inode during the call. You will likely wish to embed the -inotify_watch structure in a structure of your own which contains other -information about the watch. Once you add an inotify watch, it is immediately -subject to removal depending on filesystem events. You must grab a reference if -you depend on the watch hanging around after the call. - - inotify_init_watch(&my_watch->iwatch); - inotify_get_watch(&my_watch->iwatch); // optional - s32 wd = inotify_add_watch(ih, &my_watch->iwatch, inode, mask); - inotify_put_watch(&my_watch->iwatch); // optional - -You may use the watch descriptor (wd) or the address of the inotify_watch for -other inotify operations. You must not directly read or manipulate data in the -inotify_watch. Additionally, you must not call inotify_add_watch() more than -once for a given inotify_watch structure, unless you have first called either -inotify_rm_watch() or inotify_rm_wd(). - -To determine if you have already registered a watch for a given inode, you may -call inotify_find_watch(), which gives you both the wd and the watch pointer for -the inotify_watch, or an error if the watch does not exist. - - wd = inotify_find_watch(ih, inode, &watchp); - -You may use container_of() on the watch pointer to access your own data -associated with a given watch. When an existing watch is found, -inotify_find_watch() bumps the refcount before releasing its locks. You must -put that reference with: - - put_inotify_watch(watchp); - -Call inotify_find_update_watch() to update the event mask for an existing watch. -inotify_find_update_watch() returns the wd of the updated watch, or an error if -the watch does not exist. - - wd = inotify_find_update_watch(ih, inode, mask); - -An existing watch may be removed by calling either inotify_rm_watch() or -inotify_rm_wd(). - - int ret = inotify_rm_watch(ih, &my_watch->iwatch); - int ret = inotify_rm_wd(ih, wd); - -A watch may be removed while executing your event handler with the following: - - inotify_remove_watch_locked(ih, iwatch); - -Call inotify_destroy() to remove all watches from your inotify instance and -release it. If there are no outstanding references, inotify_destroy() will call -your destroy_watch op for each watch. - - inotify_destroy(ih); - -When inotify removes a watch, it sends an IN_IGNORED event to your callback. -You may use this event as an indication to free the watch memory. Note that -inotify may remove a watch due to filesystem events, as well as by your request. -If you use IN_ONESHOT, inotify will remove the watch after the first event, at -which point you may call the final inotify_put_watch. - -(iv) Kernel Interface Prototypes - - struct inotify_handle *inotify_init(struct inotify_operations *ops); - - inotify_init_watch(struct inotify_watch *watch); - - s32 inotify_add_watch(struct inotify_handle *ih, - struct inotify_watch *watch, - struct inode *inode, u32 mask); - - s32 inotify_find_watch(struct inotify_handle *ih, struct inode *inode, - struct inotify_watch **watchp); - - s32 inotify_find_update_watch(struct inotify_handle *ih, - struct inode *inode, u32 mask); - - int inotify_rm_wd(struct inotify_handle *ih, u32 wd); - - int inotify_rm_watch(struct inotify_handle *ih, - struct inotify_watch *watch); - - void inotify_remove_watch_locked(struct inotify_handle *ih, - struct inotify_watch *watch); - - void inotify_destroy(struct inotify_handle *ih); - - void get_inotify_watch(struct inotify_watch *watch); - void put_inotify_watch(struct inotify_watch *watch); - - -(v) Internal Kernel Implementation - -Each inotify instance is represented by an inotify_handle structure. -Inotify's userspace consumers also have an inotify_device which is -associated with the inotify_handle, and on which events are queued. - -Each watch is associated with an inotify_watch structure. Watches are chained -off of each associated inotify_handle and each associated inode. - -See fs/notify/inotify/inotify_fsnotify.c and fs/notify/inotify/inotify_user.c -for the locking and lifetime rules. - - -(vi) Rationale +(i) Rationale Q: What is the design decision behind not tying the watch to the open fd of the watched object? |