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    xfs: skip verification on initial "guess" superblock read · daba5427
    Eric Sandeen 提交于
    When xfs_readsb() does the very first read of the superblock,
    it makes a guess at the length of the buffer, based on the
    sector size of the underlying storage.  This may or may
    not match the filesystem sector size in sb_sectsize, so
    we can't i.e. do a CRC check on it; it might be too short.
    
    In fact, mounting a filesystem with sb_sectsize larger
    than the device sector size will cause a mount failure
    if CRCs are enabled, because we are checksumming a length
    which exceeds the buffer passed to it.
    
    So always read twice; the first time we read with NULL
    buffer ops to skip verification; then set the proper
    read length, hook up the proper verifier, and give it
    another go.
    
    Once we are sure that we've got the right buffer length,
    we can also use bp->b_length in the xfs_sb_read_verify,
    rather than the less-trusted on-disk sectorsize for
    secondary superblocks.  Before this we ran the risk of
    passing junk to the crc32c routines, which didn't always
    handle extreme values.
    Signed-off-by: NEric Sandeen <sandeen@redhat.com>
    Reviewed-by: NDave Chinner <dchinner@redhat.com>
    Signed-off-by: NDave Chinner <david@fromorbit.com>
    daba5427
xfs_sb.c 24.5 KB