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Merge branch 'akpm' (patches from Andrew)
Merge misc updates from Andrew Morton: "Bite-sized chunks this time, to avoid the MTA ratelimiting woes. - fs/notify updates - ocfs2 - some of MM" That laconic "some MM" is mainly the removal of remap_file_pages(), which is a big simplification of the VM, and which gets rid of a *lot* of random cruft and special cases because we no longer support the non-linear mappings that it used. From a user interface perspective, nothing has changed, because the remap_file_pages() syscall still exists, it's just done by emulating the old behavior by creating a lot of individual small mappings instead of one non-linear one. The emulation is slower than the old "native" non-linear mappings, but nobody really uses or cares about remap_file_pages(), and simplifying the VM is a big advantage. * emailed patches from Andrew Morton <[email protected]>: (78 commits) memcg: zap memcg_slab_caches and memcg_slab_mutex memcg: zap memcg_name argument of memcg_create_kmem_cache memcg: zap __memcg_{charge,uncharge}_slab mm/page_alloc.c: place zone_id check before VM_BUG_ON_PAGE check mm: hugetlb: fix type of hugetlb_treat_as_movable variable mm, hugetlb: remove unnecessary lower bound on sysctl handlers"? mm: memory: merge shared-writable dirtying branches in do_wp_page() mm: memory: remove ->vm_file check on shared writable vmas xtensa: drop _PAGE_FILE and pte_file()-related helpers x86: drop _PAGE_FILE and pte_file()-related helpers unicore32: drop pte_file()-related helpers um: drop _PAGE_FILE and pte_file()-related helpers tile: drop pte_file()-related helpers sparc: drop pte_file()-related helpers sh: drop _PAGE_FILE and pte_file()-related helpers score: drop _PAGE_FILE and pte_file()-related helpers s390: drop pte_file()-related helpers parisc: drop _PAGE_FILE and pte_file()-related helpers openrisc: drop _PAGE_FILE and pte_file()-related helpers nios2: drop _PAGE_FILE and pte_file()-related helpers ...
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Document started 15 Mar 2005 by Robert Love <[email protected]> | ||
Document updated 4 Jan 2015 by Zhang Zhen <[email protected]> | ||
--Deleted obsoleted interface, just refer to manpages for user interface. | ||
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(i) User Interface | ||
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Inotify is controlled by a set of three system calls and normal file I/O on a | ||
returned file descriptor. | ||
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First step in using inotify is to initialise an inotify instance: | ||
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int fd = inotify_init (); | ||
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Each instance is associated with a unique, ordered queue. | ||
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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. | ||
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Watches are added via a path to the file. | ||
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Watches on a directory will return events on any files inside of the directory. | ||
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Adding a watch is simple: | ||
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int wd = inotify_add_watch (fd, path, mask); | ||
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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>). | ||
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You can update an existing watch in the same manner, by passing in a new mask. | ||
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An existing watch is removed via | ||
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int ret = inotify_rm_watch (fd, wd); | ||
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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. | ||
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You can slurp multiple events by passing a large buffer, for example | ||
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size_t len = read (fd, buf, BUF_LEN); | ||
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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. | ||
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Each inotify instance fd is also select()- and poll()-able. | ||
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You can find the size of the current event queue via the standard FIONREAD | ||
ioctl on the fd returned by inotify_init(). | ||
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All watches are destroyed and cleaned up on close. | ||
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(ii) | ||
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Prototypes: | ||
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int inotify_init (void); | ||
int inotify_add_watch (int fd, const char *path, __u32 mask); | ||
int inotify_rm_watch (int fd, __u32 mask); | ||
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(iii) Kernel Interface | ||
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Inotify's kernel API consists a set of functions for managing watches and an | ||
event callback. | ||
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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. | ||
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struct inotify_handle *ih = inotify_init(my_event_handler); | ||
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You must provide a function for processing events and a function for destroying | ||
the inotify watch. | ||
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void handle_event(struct inotify_watch *watch, u32 wd, u32 mask, | ||
u32 cookie, const char *name, struct inode *inode) | ||
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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 | ||
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void destroy_watch(struct inotify_watch *watch) | ||
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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. | ||
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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 | ||
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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(). | ||
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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. | ||
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wd = inotify_find_watch(ih, inode, &watchp); | ||
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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: | ||
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put_inotify_watch(watchp); | ||
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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. | ||
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wd = inotify_find_update_watch(ih, inode, mask); | ||
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An existing watch may be removed by calling either inotify_rm_watch() or | ||
inotify_rm_wd(). | ||
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int ret = inotify_rm_watch(ih, &my_watch->iwatch); | ||
int ret = inotify_rm_wd(ih, wd); | ||
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A watch may be removed while executing your event handler with the following: | ||
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inotify_remove_watch_locked(ih, iwatch); | ||
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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. | ||
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inotify_destroy(ih); | ||
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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. | ||
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(iv) Kernel Interface Prototypes | ||
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struct inotify_handle *inotify_init(struct inotify_operations *ops); | ||
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inotify_init_watch(struct inotify_watch *watch); | ||
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s32 inotify_add_watch(struct inotify_handle *ih, | ||
struct inotify_watch *watch, | ||
struct inode *inode, u32 mask); | ||
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s32 inotify_find_watch(struct inotify_handle *ih, struct inode *inode, | ||
struct inotify_watch **watchp); | ||
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s32 inotify_find_update_watch(struct inotify_handle *ih, | ||
struct inode *inode, u32 mask); | ||
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int inotify_rm_wd(struct inotify_handle *ih, u32 wd); | ||
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int inotify_rm_watch(struct inotify_handle *ih, | ||
struct inotify_watch *watch); | ||
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void inotify_remove_watch_locked(struct inotify_handle *ih, | ||
struct inotify_watch *watch); | ||
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void inotify_destroy(struct inotify_handle *ih); | ||
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void get_inotify_watch(struct inotify_watch *watch); | ||
void put_inotify_watch(struct inotify_watch *watch); | ||
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(v) Internal Kernel Implementation | ||
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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. | ||
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Each watch is associated with an inotify_watch structure. Watches are chained | ||
off of each associated inotify_handle and each associated inode. | ||
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See fs/notify/inotify/inotify_fsnotify.c and fs/notify/inotify/inotify_user.c | ||
for the locking and lifetime rules. | ||
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(vi) Rationale | ||
(i) Rationale | ||
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Q: What is the design decision behind not tying the watch to the open fd of | ||
the watched object? | ||
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