Hi all, This is the twelfth revision of a patchset that adds to XFS kernel support for online metadata scrubbing and repair. There aren't any on-disk format changes. The first five patches add or expose various libxfs helpers that the online repair code will use to reconstruct broken metadata. Most notably we add a NORMAP flag to the bmapi functions so that we can use rmap data to rebuild block maps. Patch six allows us to disable inode reclamation temporarily for the few things that requires full filesystem scans; at the moment that is limited to the rmap rebuilder. Patches 7-20 introduce the online repair functionality for space metadata. Our general strategy for rebuilding damaged primary metadata is to rebuild the structure completely from secondary metadata and free the old structure after the fact; we do not try to salvage anything. Consequently, online repair requires rmapbt. Rebuilding the secondary metadata (rmap) is much harder -- due to our locking rules (primary and then secondary) we have to shut down the filesystem temporarily while we scan all the primary metadata for data to put in the new secondary structure. Reconstructing inodes is difficult -- the ability to rebuild files depends on the filesystem being able to load an inode (xfs_iget), which means repair has to know how to zap any part of an inode record that might trigger corruption errors from iget. To that end, we can now reset most of an inode record or an inode fork so that we can rebuild the file. The refcount rebuilder is more or less the same algorithm that xfs_repair uses, but modified to reflect the constraints of running in kernel space. For rmap rebuilds, we cannot have anything on the filesystem taking exclusive locks and we cannot have any allocation activity at all. Therefore, we start by freezing the filesystem to allow other transactions to finish. Then, we disable periodic inode reclaim and roll the freeze back just enough so that we can create our own transactions but other writes will block. Next, we scan all other AG metadata structures, every inode, and every block map to reconstruct the rmap data. Then, we reinitialize the rmap btree root and reload the rmap btree. Finally, we release all the resource we grabbed and the filesystem returns to normal. Looking forward, the parent pointer feature that Allison Henderson is working on will enable us to reconstruct directories, at which point we'll be able to reconstruct most of a lightly damaged filesystem. But that's future talk. If you're going to start using this mess, you probably ought to just pull from my git trees. The kernel patches[1] should apply against 4.16-rc2. xfsprogs[2] and xfstests[3] can be found in their usual places. The git trees contain all four series' worth of changes. This is an extraordinary way to destroy everything. Enjoy! Comments and questions are, as always, welcome. --D [1] https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=djwong-devel [2] https://git.kernel.org/cgit/linux/kernel/git/djwong/xfsprogs-dev.git/log/?h=djwong-devel [3] https://git.kernel.org/cgit/linux/kernel/git/djwong/xfstests-dev.git/log/?h=djwong-devel -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
