Hi, > On Jan 23, 2008 11:53 -0500, Theodore Tso wrote: > > Since I'm still hoping that > > some point in the future, fs/ext4 could subsume fs/ext3 so we don't > > have to worry about bug fixes going into fs/ext2 AND fs/ext3 AND > > fs/ext4, I have my own reasons for wanting that. > > If any newbie kernel hacker wants a filesystem project, allowing ext4 > to mount ext2 filesystems w/o a journal would be very useful. I > suspect that a simple flag check in the ext4_journal_* wrappers of the > jbd2 functions would be enough in many cases. > > One of the reasons to keep ext2 around is that ext3 cannot mount the > filesystem without a journal, and removing that limitation for ext4 > would bring us one step closer to removing a ton of duplicate code. > Another reason for ext2 vs. ext3 was overhead from journaling, and > that could also be removed by allowing ext4 to mount ext2 filesystems > w/o a journal. Actually, folding ext2 into ext3/4 isn't as easy as one would guess in the beginning. For example ext2 on fsync() just sync's a single inode (and has to use private_list to track metadata buffers associated with the inode) while ext3 flushes the whole journal. Also in ext2, directory handling code is quite different. ext2 works in page cache of the directory while ext3 uses page cache of the underlying device via buffer heads - at least this second thing would be more or less mechanical thing to change and would make sence (we wouldn't have to reimplement readahead in ext3 directory handling code as we do now). I've looked at it once but then more urgent things came and ... you know it. Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
