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>
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index b3d290c..84c602b 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -490,6 +490,7 @@
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 @@
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 @@
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 @@
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);