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?
projects / GitHub / LineageOS / G12 / android_kernel_amlogic_linux-4.9.git / commitdiff