• Dave Chinner's avatar
    xfs: Introduce an ordered buffer item · 5f6bed76
    Dave Chinner authored
    If we have a buffer that we have modified but we do not wish to
    physically log in a transaction (e.g. we've logged a logical
    change), we still need to ensure that transactional integrity is
    maintained. Hence we must not move the tail of the log past the
    transaction that the buffer is associated with before the buffer is
    written to disk.
    
    This means these special buffers still need to be included in the
    transaction and added to the AIL just like a normal buffer, but we
    do not want the modifications to the buffer written into the
    transaction. IOWs, what we want is an "ordered buffer" that
    maintains the same transactional life cycle as a physically logged
    buffer, just without the transcribing of the modifications to the
    log.
    
    Hence we need to flag the buffer as an "ordered buffer" to avoid
    including it in vector size calculations or formatting during the
    transaction. Once the transaction is committed, the buffer appears
    for all intents to be the same as a physically logged buffer as it
    transitions through the log and AIL.
    
    Relogging will also work just fine for such an ordered buffer - the
    logical transaction will be replayed before the subsequent
    modifications that relog the buffer, so everything will be
    reconstructed correctly by recovery.
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
    Reviewed-by: default avatarMark Tinguely <tinguely@sgi.com>
    Signed-off-by: default avatarBen Myers <bpm@sgi.com>
    5f6bed76
xfs_trans_buf.c 23.1 KB