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    ext4, jbd2: Add barriers for file systems with exernal journals · cc3e1bea
    Theodore Ts'o 提交于
    This is a bit complicated because we are trying to optimize when we
    send barriers to the fs data disk.  We could just throw in an extra
    barrier to the data disk whenever we send a barrier to the journal
    disk, but that's not always strictly necessary.
    
    We only need to send a barrier during a commit when there are data
    blocks which are must be written out due to an inode written in
    ordered mode, or if fsync() depends on the commit to force data blocks
    to disk.  Finally, before we drop transactions from the beginning of
    the journal during a checkpoint operation, we need to guarantee that
    any blocks that were flushed out to the data disk are firmly on the
    rust platter before we drop the transaction from the journal.
    
    Thanks to Oleg Drokin for pointing out this flaw in ext3/ext4.
    Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
    cc3e1bea
fsync.c 3.3 KB