vfs: improve i_op->atomic_open() documentation

Fix documentation of ->atomic_open() and related functions: finish_open()
and finish_no_open().  Also add details that seem to be unclear and a
source of bugs (some of which are fixed in the following series).

Cc-ing maintainers of all filesystems implementing ->atomic_open().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Sage Weil <sage@inktank.com>
Cc: Steve French <sfrench@samba.org>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/vfs.txt

@@ -359,11 +359,9 @@ struct inode_operations {
 	ssize_t (*listxattr) (struct dentry *, char *, size_t);
 	int (*removexattr) (struct dentry *, const char *);
 	void (*update_time)(struct inode *, struct timespec *, int);
-	int (*atomic_open)(struct inode *, struct dentry *,
+	int (*atomic_open)(struct inode *, struct dentry *, struct file *,
+			unsigned open_flag, umode_t create_mode, int *opened);
 	int (*tmpfile) (struct inode *, struct dentry *, umode_t);
-} ____cacheline_aligned;
-				struct file *, unsigned open_flag,
-				umode_t create_mode, int *opened);
 };
 
 Again, all methods are called without any locks being held, unless
@@ -470,9 +468,11 @@ otherwise noted.
   	method the filesystem can look up, possibly create and open the file in
   	one atomic operation.  If it cannot perform this (e.g. the file type
   	turned out to be wrong) it may signal this by returning 1 instead of
-  	usual 0 or -ve .  This method is only called if the last
-  	component is negative or needs lookup.  Cached positive dentries are
-  	still handled by f_op->open().
+	usual 0 or -ve .  This method is only called if the last component is
+	negative or needs lookup.  Cached positive dentries are still handled by
+	f_op->open().  If the file was created, the FILE_CREATED flag should be
+	set in "opened".  In case of O_EXCL the method must only succeed if the
+	file didn't exist and hence FILE_CREATED shall always be set on success.
 
   tmpfile: called in the end of O_TMPFILE open().  Optional, equivalent to
 	atomically creating, opening and unlinking a file in given directory.