Commit 020ac5b6 authored May 31, 2012 by Artem Bityutskiy Committed by Linus Torvalds May 31, 2012

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: 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>

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 */

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