• Takashi Sato's avatar
    filesystem freeze: add error handling of write_super_lockfs/unlockfs · c4be0c1d
    Takashi Sato authored
    Currently, ext3 in mainline Linux doesn't have the freeze feature which
    suspends write requests.  So, we cannot take a backup which keeps the
    filesystem's consistency with the storage device's features (snapshot and
    replication) while it is mounted.
    
    In many case, a commercial filesystem (e.g.  VxFS) has the freeze feature
    and it would be used to get the consistent backup.
    
    If Linux's standard filesystem ext3 has the freeze feature, we can do it
    without a commercial filesystem.
    
    So I have implemented the ioctls of the freeze feature.
    I think we can take the consistent backup with the following steps.
    1. Freeze the filesystem with the freeze ioctl.
    2. Separate the replication volume or create the snapshot
       with the storage device's feature.
    3. Unfreeze the filesystem with the unfreeze ioctl.
    4. Take the backup from the separated replication volume
       or the snapshot.
    
    This patch:
    
    VFS:
    Changed the type of write_super_lockfs and unlockfs from "void"
    to "int" so that they can return an error.
    Rename write_super_lockfs and unlockfs of the super block operation
    freeze_fs and unfreeze_fs to avoid a confusion.
    
    ext3, ext4, xfs, gfs2, jfs:
    Changed the type of write_super_lockfs and unlockfs from "void"
    to "int" so that write_super_lockfs returns an error if needed,
    and unlockfs always returns 0.
    
    reiserfs:
    Changed the type of write_super_lockfs and unlockfs from "void"
    to "int" so that they always return 0 (success) to keep a current behavior.
    Signed-off-by: default avatarTakashi Sato <t-sato@yk.jp.nec.com>
    Signed-off-by: default avatarMasayuki Hamaguchi <m-hamaguchi@ys.jp.nec.com>
    Cc: <xfs-masters@oss.sgi.com>
    Cc: <linux-ext4@vger.kernel.org>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Dave Kleikamp <shaggy@austin.ibm.com>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Alasdair G Kergon <agk@redhat.com>
    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>
    c4be0c1d
super.c 83.8 KB