On Tue, Apr 24, 2007 at 04:53:11PM -0500, Amit Gud wrote: > Nikita Danilov wrote: > >Maybe I failed to describe the problem presicely. > > > >Suppose that all chunks have been checked. After that, for every inode > >I0 having continuations I1, I2, ... In, one has to check that every > >logical block is presented in at most one of these inodes. For this one > >has to read I0, with all its indirect (double-indirect, triple-indirect) > >blocks, then read I1 with all its indirect blocks, etc. And to repeat > >this for every inode with continuations. > > > >In the worst case (every inode has a continuation in every chunk) this > >obviously is as bad as un-chunked fsck. But even in the average case, > >total amount of io necessary for this operation is proportional to the > >_total_ file system size, rather than to the chunk size. > > > > Perhaps, I should talk about how continuation inodes are managed / > located on disk. (This is how it is in my current implementation) > > 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? 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. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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
