Merge branch 'akpm' (patches from Andrew)

	about doing this.

	The idea is, first at flush_dcache_page() time, if

	page->mapping->i_mmap is an empty tree and ->i_mmap_nonlinear

	an empty list, just mark the architecture private page flag bit.

	Later, in update_mmu_cache(), a check is made of this flag bit,

	and if set the flush is done and the flag bit is cleared.

	page->mapping->i_mmap is an empty tree, just mark the architecture

	private page flag bit.  Later, in update_mmu_cache(), a check is

	made of this flag bit, and if set the flush is done and the flag

	bit is cleared.

	IMPORTANT NOTE: It is often important, if you defer the flush,

			that the actual flush occurs on the same CPU

};

It is intended that the file system should not need to access any of this

structure directly.

structure directly. Filesystem handlers should be tolerant to signals and return

EINTR once fatal signal received.

Flag checking should be done at the beginning of the ->fiemap callback via the

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?

coherency=buffered	Allow concurrent O_DIRECT writes without EX lock among

			nodes, which gains high performance at risk of getting

			stale data on other nodes.

journal_async_commit	Commit block can be written to disk without waiting

			for descriptor blocks. If enabled older kernels cannot

			mount the device. This will enable 'journal_checksum'

			internally.

virtual address space. This use-case is not critical anymore since 64-bit

systems are widely available.

The plan is to deprecate the syscall and replace it with an emulation.

The emulation will create new VMAs instead of nonlinear mappings. It's

going to work slower for rare users of remap_file_pages() but ABI is

preserved.

The syscall is deprecated and replaced it with an emulation now. The

emulation creates new VMAs instead of nonlinear mappings. It's going to

work slower for rare users of remap_file_pages() but ABI is preserved.

One side effect of emulation (apart from performance) is that user can hit

vm.max_map_count limit more easily due to additional VMAs. See comment for