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Commit 020ac5b6 authored by Artem Bityutskiy's avatar Artem Bityutskiy Committed by Linus Torvalds
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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 <artem.bityutskiy@linux.intel.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7bc1bac7

fs/fat/fat.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

fs/fat/inode.c

+12 −0
Original line number Diff line number Diff line
@@ -490,6 +490,7 @@ static void fat_put_super(struct super_block *sb) 
	if (sb->s_dirt)

		fat_write_super(sb);



	iput(sbi->fsinfo_inode);

	iput(sbi->fat_inode);



	unload_nls(sbi->nls_disk);
@@ -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;

	insert_inode_hash(fsinfo_inode);



	root_inode = new_inode(sb);

	if (!root_inode)

		goto out_fail;
@@ -1516,6 +1526,8 @@ out_invalid: 
		fat_msg(sb, KERN_INFO, "Can't find a valid FAT filesystem");



out_fail:

	if (fsinfo_inode)

		iput(fsinfo_inode);

	if (fat_inode)

		iput(fat_inode);

	unload_nls(sbi->nls_io);

include/linux/msdos_fs.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */