affs: get rid of affs_sync_super

This patch makes affs stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/affs/affs.h

@@ -3,6 +3,7 @@
 #include <linux/buffer_head.h>
 #include <linux/amigaffs.h>
 #include <linux/mutex.h>
+#include <linux/workqueue.h>
 
 /* AmigaOS allows file names with up to 30 characters length.
  * Names longer than that will be silently truncated. If you
@@ -101,6 +102,9 @@ struct affs_sb_info {
 	char s_volume[32];		/* Volume prefix for absolute symlinks. */
 	spinlock_t symlink_lock;	/* protects the previous two */
 	struct super_block *sb;		/* the VFS superblock object */
+	int work_queued;		/* non-zero delayed work is queued */
+	struct delayed_work sb_work;	/* superblock flush delayed work */
+	spinlock_t work_lock;		/* protects sb_work and work_queued */
 };
 
 #define SF_INTL		0x0001		/* International filesystem. */
@@ -121,6 +125,8 @@ static inline struct affs_sb_info *AFFS_SB(struct super_block *sb)
 	return sb->s_fs_info;
 }
 
+void affs_mark_sb_dirty(struct super_block *sb);
+
 /* amigaffs.c */
 
 extern int	affs_insert_hash(struct inode *inode, struct buffer_head *bh);