On Sep 14, 2006 15:21 +0200, Alexandre Ratchov wrote: > IMHO, the natural place to do this stuff is the VFS, because it can be > common to all file-systems supporting this feature. Currently it's the same > with ctime, mtime and atime. These are in the VFS even if there are > file-systems that don't support all of them. Well, that is only partly true. I see lots of places in ext3 that are setting i_ctime and i_mtime... > > Ugh, this would definitely hurt performance, because ext3_dirty_inode() > > packs-for-disk the whole inode each time. I believe Stephen had patches > > at one time to do the inode packing at transaction commit time instead > > of when it is changed, so we only do the packing once. Having a generic > > mechanism to do pre-commit callbacks from jbd (i.e. to pack a dirty > > inode to the buffer) would also be useful for other things like doing > > the inode or group descriptor checksum only once per transaction... > > afaik, for an open file, there is always a copy of the inode in memory, > because there is a reference to it in the file structure. So, in principle, > we shouldn't need to make dirty the inode. I don't know if this is feasable > perhaps am i missing something here. The in-memory inode needs to be copied into the buffer so that it is part of the transaction being committed to disk, or updates are lost. This was a common bug with early ext3 - marking the inode dirty and then changing a field in the in-core inode - which would not be saved to disk. In other filesystems this is only a few-cycle race, but in ext3 the in-core inode is not written to disk unless the inode is again marked dirty. The potential benefit of making this a callback from the JBD layer is it avoids copying the inode for EVERY dirty, and only doing it once per transaction. Add a list of callbacks hooked onto the transaction to be called before it is committed, and the callback data is the inode pointer which does a single ext3_do_update_inode() call if the inode is still marked dirty. > it's not strictly necessary; it's not more necessary that the interface to > ctime or other attributes. It's here for completness, in my opinion the > change attribute is the same as the ctime time-stamp Then makes sense to just improve the ctime mechanism instead of adding new code and interfaces... Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - 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
