• Joel Becker's avatar
    jbd2: Add buffer triggers · e06c8227
    Joel Becker authored
    Filesystems often to do compute intensive operation on some
    metadata.  If this operation is repeated many times, it can be very
    expensive.  It would be much nicer if the operation could be performed
    once before a buffer goes to disk.
    This adds triggers to jbd2 buffer heads.  Just before writing a metadata
    buffer to the journal, jbd2 will optionally call a commit trigger associated
    with the buffer.  If the journal is aborted, an abort trigger will be
    called on any dirty buffers as they are dropped from pending
    ocfs2 will use this feature.
    Initially I tried to come up with a more generic trigger that could be
    used for non-buffer-related events like transaction completion.  It
    doesn't tie nicely, because the information a buffer trigger needs
    (specific to a journal_head) isn't the same as what a transaction
    trigger needs (specific to a tranaction_t or perhaps journal_t).  So I
    implemented a buffer set, with the understanding that
    journal/transaction wide triggers should be implemented separately.
    There is only one trigger set allowed per buffer.  I can't think of any
    reason to attach more than one set.  Contrast this with a journal or
    transaction in which multiple places may want to watch the entire
    transaction separately.
    The trigger sets are considered static allocation from the jbd2
    perspective.  ocfs2 will just have one trigger set per block type,
    setting the same set on every bh of the same type.
    Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
    Cc: "Theodore Ts'o" <tytso@mit.edu>
    Cc: <linux-ext4@vger.kernel.org>
    Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
journal-head.h 2.49 KB