update VFS documentation for method changes.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/Locking

@@ -92,8 +92,8 @@ prototypes:
 	void (*destroy_inode)(struct inode *);
 	void (*dirty_inode) (struct inode *);
 	int (*write_inode) (struct inode *, int);
-	void (*drop_inode) (struct inode *);
-	void (*delete_inode) (struct inode *);
+	int (*drop_inode) (struct inode *);
+	void (*evict_inode) (struct inode *);
 	void (*put_super) (struct super_block *);
 	void (*write_super) (struct super_block *);
 	int (*sync_fs)(struct super_block *sb, int wait);
@@ -101,14 +101,13 @@ prototypes:
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
-	void (*clear_inode) (struct inode *);
 	void (*umount_begin) (struct super_block *);
 	int (*show_options)(struct seq_file *, struct vfsmount *);
 	ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
 	ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
 
 locking rules:
-	All may block.
+	All may block [not true, see below]
 	None have BKL
 			s_umount
 alloc_inode:
@@ -116,22 +115,25 @@ destroy_inode:
 dirty_inode:				(must not sleep)
 write_inode:
 drop_inode:				!!!inode_lock!!!
-delete_inode:
+evict_inode:
 put_super:		write
 write_super:		read
 sync_fs:		read
 freeze_fs:		read
 unfreeze_fs:		read
-statfs:			no
-remount_fs:		maybe		(see below)
-clear_inode:
+statfs:			maybe(read)	(see below)
+remount_fs:		write
 umount_begin:		no
 show_options:		no		(namespace_sem)
 quota_read:		no		(see below)
 quota_write:		no		(see below)
 
-->remount_fs() will have the s_umount exclusive lock if it's already mounted.
-When called from get_sb_single, it does NOT have the s_umount lock.
+->statfs() has s_umount (shared) when called by ustat(2) (native or
+compat), but that's an accident of bad API; s_umount is used to pin
+the superblock down when we only have dev_t given us by userland to
+identify the superblock.  Everything else (statfs(), fstatfs(), etc.)
+doesn't hold it when calling ->statfs() - superblock is pinned down
+by resolving the pathname passed to syscall.
 ->quota_read() and ->quota_write() functions are both guaranteed to
 be the only ones operating on the quota file by the quota code (via
 dqio_sem) (unless an admin really wants to screw up something and

Documentation/filesystems/porting

@@ -291,3 +291,30 @@ be in order of zeroing blocks using block_truncate_page or similar helpers,
 size update and on finally on-disk truncation which should not fail.
 inode_change_ok now includes the size checks for ATTR_SIZE and must be called
 in the beginning of ->setattr unconditionally.
+
+[mandatory]
+
+	->clear_inode() and ->delete_inode() are gone; ->evict_inode() should
+be used instead.  It gets called whenever the inode is evicted, whether it has
+remaining links or not.  Caller does *not* evict the pagecache or inode-associated
+metadata buffers; getting rid of those is responsibility of method, as it had
+been for ->delete_inode().
+	->drop_inode() returns int now; it's called on final iput() with inode_lock
+held and it returns true if filesystems wants the inode to be dropped.  As before,
+generic_drop_inode() is still the default and it's been updated appropriately.
+generic_delete_inode() is also alive and it consists simply of return 1.  Note that
+all actual eviction work is done by caller after ->drop_inode() returns.
+	clear_inode() is gone; use end_writeback() instead.  As before, it must
+be called exactly once on each call of ->evict_inode() (as it used to be for
+each call of ->delete_inode()).  Unlike before, if you are using inode-associated
+metadata buffers (i.e. mark_buffer_dirty_inode()), it's your responsibility to
+call invalidate_inode_buffers() before end_writeback().
+	No async writeback (and thus no calls of ->write_inode()) will happen
+after end_writeback() returns, so actions that should not overlap with ->write_inode()
+(e.g. freeing on-disk inode if i_nlink is 0) ought to be done after that call.
+
+	NOTE: checking i_nlink in the beginning of ->write_inode() and bailing out
+if it's zero is not *and* *never* *had* *been* enough.  Final unlink() and iput()
+may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly
+free the on-disk inode, you may end up doing that while ->write_inode() is writing
+to it.