Date:	Thu, 5 Feb 2015 15:49:16 +0100
From:	Jan Kara <jack@...e.cz>
To:	Zhang Zhen <zhenzhang.zhang@...wei.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	morgan.wang@...wei.com, eparis@...isplace.org,
	robert.w.love@...el.com, john@...nmccutchan.com,
	Heinrich Schuchardt <xypron.glpk@....de>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v2] inotify: update documentation to reflect code changes

On Wed 04-02-15 11:01:56, Zhang Zhen wrote:
> The inotify interface has changed a lot. The user interface was
> too old, and the kernel interface was removed by Eric Paris in
> commit: 2dfc1ca inotify: remove inotify in kernel interface.
> 
> Change v1 -> v2:
> - Deleted the user interface following Heinrich's and Honza's suggestion
> 
> Signed-off-by: Zhang Zhen <zhenzhang.zhang@...wei.com>
  You can add:
Acked-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  Documentation/filesystems/inotify.txt | 197 +---------------------------------
>  1 file changed, 3 insertions(+), 194 deletions(-)
> 
> diff --git a/Documentation/filesystems/inotify.txt b/Documentation/filesystems/inotify.txt
> index cfd0271..51f61db 100644
> --- a/Documentation/filesystems/inotify.txt
> +++ b/Documentation/filesystems/inotify.txt
> @@ -4,201 +4,10 @@
> 
> 
>  Document started 15 Mar 2005 by Robert Love <rml@...ell.com>
> +Document updated 4 Jan 2015 by Zhang Zhen <zhenzhang.zhang@...wei.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?
> -- 
> 1.8.5.5
> 
> 
> .
> 
> 
> 
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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