Dave Chinner <david@xxxxxxxxxxxxx> writes: > On Wed, Feb 13, 2013 at 10:13:16AM -0800, Eric W. Biederman wrote: > >> The crazy thing is that is that xfs appears to >> directly write their incore inode structure into their journal. > > Off topic, but it's actually a very sane thing to do. It's called > logical object logging, as opposed to physical logging like ext3/4 > and ocfs2 use. XFS uses a combination of logical logging > (superblock, dquots, inodes) and physical logging (via buffers). Not putting your structures in disk-endian before putting them on-disk seems silly. As far as I can tell if you switch endianness of the machine accessing your xfs filesystem and have to do a log recover it won't work because a lot of the log entries will appear corrupted. It also seems silly to require your in-memory structure to be binary compatibile with your log when you immediately copy that structure to another buffer when it comes time to queue a version of it to put into the log. The fact that you sometimes need to allocate memory and make a copy so you can stuff your data into the logvec whose only purpose is to then copy the data a second time seems silly and wasteful. Logical logging itself seems reasonable. I just find the implementation in xfs odd. It looks like with a few little changes xfs could retain backwards compatibility with today, remove extra memory copies, and completely decouple the format of the in-core structures with the format of the on-disk structures. Allowing scary comments to be removed. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
