On Mon, Jan 28, 2013 at 03:27:38PM -0800, David Lang wrote: > On Mon, 28 Jan 2013, Theodore Ts'o wrote: > > >On Sun, Jan 27, 2013 at 10:13:37PM -0800, Daniel Phillips wrote: > >>>The thing that jumps out at me with this is the question of how you will > >>>avoid the 'filesystem image in a file' disaster that reiserfs had (where > >>>it's fsck could mix up metadata chunks from the main filesystem with > >>>metadata chunks from any filesystem images that it happened to stumble > >>>across when scanning the disk) Did that ever get fixed in reiserfs? > >>> > >>Only superficially. Deep thoughts are in order. First, there needs to be a > >>hole in the filesystem structure, before we would even consider trying to > >>plug something in there. Once we know there is a hole, we want to > >>narrow down the list of candidates to fill it. If a candidate already lies > >>within a perfectly viable file, obviously we would not want to interpret > >>that as lost metadata. Unless the filesystem is really mess up... > >> > >>That is about as far as I have got with the analysis. Clearly, much more > >>is required. Suggestions welcome. > > > >The obvious answer is what resierfs4 ultimately ended up using. Drop > >a file system UUID in the superblock; mix the UUID into a checksum > >which protects each of the your metadata blocks. We're mixing in the > >inode number as well as the fs uuid in in ext4's new metadata checksum > >feature to protect against an inode table block getting written to the > >wrong location on disk. It will also mean that e2fsck won't mistake > >an inode table from an earlier mkfs with the current file system. > >This will allow us to avoid needing to zero the inode table for newly > >initialized file systems. > > The situation I'm thinking of is when dealing with VMs, you make a > filesystem image once and clone it multiple times. Won't that end up > with the same UUID in the superblock? Yes, but one ought to be able to change the UUID a la tune2fs -U. Even still... so long as the VM images have a different UUID than the fs that they live on, it ought to be fine. --D > > David Lang > -- > 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 -- 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
