Commit 78491189 authored by Artem Bityutskiy's avatar Artem Bityutskiy Committed by Linus Torvalds

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: 's avatarArtem Bityutskiy <>
Cc: OGAWA Hirofumi <>
Cc: Al Viro <>
Signed-off-by: 's avatarAndrew Morton <>
Signed-off-by: 's avatarLinus Torvalds <>
parent 330fe3c4
......@@ -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)
__mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
static inline int fat_ent_update_ptr(struct super_block *sb,
......@@ -459,37 +459,10 @@ static void fat_evict_inode(struct inode *inode)
static void fat_write_super(struct super_block *sb)
sb->s_dirt = 0;
if (!(sb->s_flags & MS_RDONLY))
static int fat_sync_fs(struct super_block *sb, int wait)
int err = 0;
if (sb->s_dirt) {
sb->s_dirt = 0;
err = fat_clusters_flush(sb);
return err;
static void fat_put_super(struct super_block *sb)
struct msdos_sb_info *sbi = MSDOS_SB(sb);
if (sb->s_dirt)
......@@ -662,7 +635,18 @@ static int __fat_write_inode(struct inode *inode, int wait)
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;
err = fat_clusters_flush(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,
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