• Artem Bityutskiy's avatar
    fat: switch to fsinfo_inode · 78491189
    Artem Bityutskiy authored
    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: 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>
    78491189
fatent.c 16.6 KB