On Apr 25, 2007 20:54 +1000, David Chinner wrote: > On Tue, Apr 24, 2007 at 04:53:11PM -0500, Amit Gud wrote: > > Right now, there is no distinction between an inode and continuation > > inode (also referred to as 'cnode' below), except for the > > EXT2_IS_CONT_FL flag. Every inode holds a list of static number of > > inodes, currently limited to 4. > > > > The structure looks like this: > > > > ---------- ---------- > > | cnode 0 |---------->| cnode 0 |----------> to another cnode or NULL > > ---------- ---------- > > | cnode 1 |----- | cnode 1 |----- > > ---------- | ---------- | > > | cnode 2 |-- | | cnode 2 |-- | > > ---------- | | ---------- | | > > | cnode 3 | | | | cnode 3 | | | > > ---------- | | ---------- | | > > | | | | | | > > > > inodes inodes or NULL > > How do you recover if fsfuzzer takes out a cnode in the chain? The > chunk is marked clean, but clearly corrupted and needs fixing and > you don't know what it was pointing at. Hence you have a pointer to > a trashed cnode *somewhere* that you need to find and fix, and a > bunch of orphaned cnodes that nobody points to *somewhere else* in > the filesystem that you have to find. That's a full scan fsck case, > isn't? Presumably, the cnodes in the other chunks contain forward and back references. Those need to contain at minimum inode + generation + chunk to avoid problem of pointing to a _different_ inode after such corruption caused the old inode to be deleted and a new one allocated in its place. If the cnode in each chunk is more than just a singly-linked list, the file as a whole could survive multiple chunk corruptions, though there would now be holes in the file. > It seems that any sort of damage to the underlying storage (e.g. > media error, I/O error or user brain explosion) results in the need > to do a full fsck and hence chunkfs gives you no benefit in this > case. There are several cases where such corruption could be found: - file access from the "parent" cnode will be missing corrupted cnode, probably causing a fsck of both the source and target chunks - a fsck of the source chunk would find the dangling cnode reference and cause a fsck of the corrupt chunk - a fsck of the later cnode chunks would find the dangling cnode reference and cause a fsck of the corrupt chunk - a fsck of the corrupt chunk would find the original corruption The case where only a fsck of the corrupt chunk is done would not find the cnode references. Maybe there needs to be per-chunk info which contains a list/bitmap of other chunks that have cnodes shared with each chunk? Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - 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
