• Steven Whitehouse's avatar
    GFS2: Tag all metadata with jid · 0ab7d13f
    Steven Whitehouse authored
    There are two spare field in the header common to all GFS2
    metadata. One is just the right size to fit a journal id
    in it, and this patch updates the journal code so that each
    time a metadata block is modified, we tag it with the journal
    id of the node which is performing the modification.
    
    The reason for this is that it should make it much easier to
    debug issues which arise if we can tell which node was the
    last to modify a particular metadata block.
    
    Since the field is updated before the block is written into
    the journal, each journal should only contain metadata which
    is tagged with its own journal id. The one exception to this
    is the journal header block, which might have a different node's
    id in it, if that journal was recovered by another node in the
    cluster.
    
    Thus each journal will contain a record of which nodes recovered
    it, via the journal header.
    
    The other field in the metadata header could potentially be
    used to hold information about what kind of operation was
    performed, but for the time being we just zero it on each
    transaction so that if we use it for that in future, we'll
    know that the information (where it exists) is reliable.
    
    I did consider using the other field to hold the journal
    sequence number, however since in GFS2's journaling we write
    the modified data into the journal and not the original
    data, this gives no information as to what action caused the
    modification, so I think we can probably come up with a better
    use for those 64 bits in the future.
    Signed-off-by: default avatarSteven Whitehouse <swhiteho@redhat.com>
    0ab7d13f
log.c 23.1 KB