fat: switch to fsinfo_inode

Currently FAT file-system maps the VFS "superblock" abstraction to the
FSINFO block.  The FSINFO block contains non-essential data about the
amount of free clusters and the next free cluster.  FAT file-system can
always find out this information by scanning the FAT table, but having it
in the FSINFO block may speed things up sometimes.  So FAT file-system
relies on the VFS superblock write-out services to make sure the FSINFO
block is written out to the media from time to time.

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 superblock 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 no matter what.  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.

This patch switches the FAT FSINFO block management from
'->write_super()'/'->s_dirt' to 'fsinfo_inode'/'->write_inode'.  Now,
instead of setting the 's_dirt' flag, we just mark the special
'fsinfo_inode' inode as dirty and let VFS invoke the '->write_inode'
call-back when needed, where we write-out the FSINFO block.

This patch also makes sure we do not mark the 'fsinfo_inode' inode as
dirty if we are not FAT32 (FAT16 and FAT12 do not have the FSINFO block)
or if we are in R/O mode.

As a bonus, we can also remove the '->sync_fs()' and '->write_super()' FAT
call-back function because they become unneeded.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 18 insertions, 31 deletions

diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index 81815487e04d..31f08ab62c56 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -310,7 +310,12 @@ void fat_ent_access_init(struct super_block *sb)
 
 static void mark_fsinfo_dirty(struct super_block *sb)
 {
-        sb->s_dirt = 1;
+        struct msdos_sb_info *sbi = MSDOS_SB(sb);
+
+        if (sb->s_flags & MS_RDONLY || sbi->fat_bits != 32)
+                return;
+
+        __mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
 }
 
 static inline int fat_ent_update_ptr(struct super_block *sb,
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 84c602b4bb25..c2973ea5df9a 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -459,37 +459,10 @@ static void fat_evict_inode(struct inode *inode)
         fat_detach(inode);
 }
 
-static void fat_write_super(struct super_block *sb)
-{
-        lock_super(sb);
-        sb->s_dirt = 0;
-
-        if (!(sb->s_flags & MS_RDONLY))
-                fat_clusters_flush(sb);
-        unlock_super(sb);
-}
-
-static int fat_sync_fs(struct super_block *sb, int wait)
-{
-        int err = 0;
-
-        if (sb->s_dirt) {
-                lock_super(sb);
-                sb->s_dirt = 0;
-                err = fat_clusters_flush(sb);
-                unlock_super(sb);
-        }
-
-        return err;
-}
-
 static void fat_put_super(struct super_block *sb)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 
-        if (sb->s_dirt)
-                fat_write_super(sb);
-
         iput(sbi->fsinfo_inode);
         iput(sbi->fat_inode);
 
@@ -662,7 +635,18 @@ retry:
 
 static int fat_write_inode(struct inode *inode, struct writeback_control *wbc)
 {
-        return __fat_write_inode(inode, wbc->sync_mode == WB_SYNC_ALL);
+        int err;
+
+        if (inode->i_ino == MSDOS_FSINFO_INO) {
+                struct super_block *sb = inode->i_sb;
+
+                lock_super(sb);
+                err = fat_clusters_flush(sb);
+                unlock_super(sb);
+        } else
+                err = __fat_write_inode(inode, wbc->sync_mode == WB_SYNC_ALL);
+
+        return err;
 }
 
 int fat_sync_inode(struct inode *inode)
@@ -679,8 +663,6 @@ static const struct super_operations fat_sops = {
         .write_inode    = fat_write_inode,
         .evict_inode    = fat_evict_inode,
         .put_super      = fat_put_super,
-        .write_super    = fat_write_super,
-        .sync_fs        = fat_sync_fs,
         .statfs         = fat_statfs,
         .remount_fs     = fat_remount,