Commit 020ac5b6 authored by Artem Bityutskiy's avatar Artem Bityutskiy Committed by Linus Torvalds

fat: introduce special inode for managing the FSINFO block

This is patchset makes fatfs stop using the VFS '->write_super()' method
for writing out the FSINFO block.

The final goal is to get rid of the 'sync_supers()' kernel thread.  This
kernel thread wakes up every 5 seconds (by default) and calls
'->write_super()' for all mounted file-systems.  And the bad thing is that
this is done even if all the superblocks are clean.  Moreover, some
file-systems do not even need this end they do not register the
'->write_super()' method at all (e.g., btrfs).

So 'sync_supers()' most often just generates useless wake-ups and wastes
power.  I am trying to make all file-systems independent of
'->write_super()' and plan to remove 'sync_supers()' and '->write_super'
completely once there are no more users.

The '->write_supers()' method is mostly used by baroque file-systems like
hfs, udf, etc.  Modern file-systems like btrfs and xfs do not use it.
This justifies removing this stuff from VFS completely and make every FS
self-manage own superblock.

Tested with xfstests.

This patch:

Preparation for further changes.  It introduces a special inode
('fsinfo_inode') in FAT file-system which we'll later use for managing the
FSINFO block.  Note, this there is already one special inode ('fat_inode')
which is used for managing the FAT tables.

Introduce new 'MSDOS_FSINFO_INO' constant for this special inode.  It is
safe to do because FAT file-system does not store inode numbers on the
media but generates them run-time.

I've also cleaned up the comment to existing 'MSDOS_ROOT_INO' constant,
while on it.
Signed-off-by: default avatarArtem Bityutskiy <>
Cc: OGAWA Hirofumi <>
Cc: Al Viro <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7bc1bac7
......@@ -82,6 +82,7 @@ struct msdos_sb_info {
int fatent_shift;
struct fatent_operations *fatent_ops;
struct inode *fat_inode;
struct inode *fsinfo_inode;
struct ratelimit_state ratelimit;
......@@ -490,6 +490,7 @@ static void fat_put_super(struct super_block *sb)
if (sb->s_dirt)
......@@ -1244,6 +1245,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
void (*setup)(struct super_block *))
struct inode *root_inode = NULL, *fat_inode = NULL;
struct inode *fsinfo_inode = NULL;
struct buffer_head *bh;
struct fat_boot_sector *b;
struct msdos_sb_info *sbi;
......@@ -1490,6 +1492,14 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
goto out_fail;
MSDOS_I(fat_inode)->i_pos = 0;
sbi->fat_inode = fat_inode;
fsinfo_inode = new_inode(sb);
if (!fsinfo_inode)
goto out_fail;
fsinfo_inode->i_ino = MSDOS_FSINFO_INO;
sbi->fsinfo_inode = fsinfo_inode;
root_inode = new_inode(sb);
if (!root_inode)
goto out_fail;
......@@ -1516,6 +1526,8 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
fat_msg(sb, KERN_INFO, "Can't find a valid FAT filesystem");
if (fsinfo_inode)
if (fat_inode)
......@@ -21,8 +21,9 @@
#define CT_LE_W(v) cpu_to_le16(v)
#define CT_LE_L(v) cpu_to_le32(v)
#define MSDOS_ROOT_INO 1 /* The root inode number */
#define MSDOS_FSINFO_INO 2 /* Used for managing the FSINFO block */
#define MSDOS_ROOT_INO 1 /* == MINIX_ROOT_INO */
#define MSDOS_DIR_BITS 5 /* log2(sizeof(struct msdos_dir_entry)) */
/* directory limit */
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