Hi all, This is the fifth revision of a patchset that adds to XFS kernel support for online metadata scrubbing and repair. There aren't any on-disk format changes. Changes since v4 include numerous bug fixes, somewhat more aggressive log flushing so that on-disk metadata, and the ability to distinguish between metadata that's obviously corrupt and metadata that merely fails cross-referencing checks in the status that is sent back to userspace. I have also begun using it to check all my development workstations, which has been useful for flushing out more bugs. Online scrub/repair support consists of four major pieces -- first, an ioctl that maps physical extents to their owners; second, various in-kernel metadata scrubbing ioctls to examine metadata records and cross-reference them with other filesystem metadata; third, an in-kernel mechanism for rebuilding damaged metadata objects and btrees; and fourth, a userspace component to initiate kernel scrubbing, walk all inodes and the directory tree, scrub data extents, and ask the kernel to repair anything that is broken. This new utility, xfs_scrub, is separate from the existing offline xfs_repair tool. Scrub has three main modes of operation -- in its most powerful mode, it iterates all XFS metadata and asks the kernel to check the metadata and repair it if necessary. The second most powerful mode can use certain VFS methods and XFS ioctls (BULKSTAT, GETBMAP, and GETFSMAP) to check as much metadata as it reasonably can from userspace. It cannot repair anything. The least powerful mode uses only VFS functions to access as much of the directory/file/xattr graph as possible. It has no mechanism to check internal metadata and also cannot repair anything. This is good enough for scrubbing non-XFS filesystems, but the primary goal is first-class XFS support. As usual, the first patches in this series are bug fixes for problems discovered while running the code through rigorous fuzz testing. The next few patches in this series implements the GETFSMAP ioctl that maps a device number and physical extent either to filesystem metadata or to a range of file blocks. The initial implementation uses the reverse-mapping B+tree to supply the mapping information, however a fallback implementation based on the free space btrees is also provided. The flexibility of having both implementations is important when it comes to the userspace tool -- even without the owner/offset data, we still have enough information to set up a read verification. There's also a patch to enable xfs_scrub to query the per-AG block reservations so that the summary counters can be sanity-checked. The next big chunk of patches implement in-kernel scrubbing. This is implemented as a new ioctl. Pass in a metadata type and control data such as an AG number or inode (when applicable); the kernel will examine each record in that metadata structure looking for obvious logical errors. External corruption should be discoverable via the checksum embedded in each (v5) filesystem metadata block. When applicable, the metadata record will be cross-referenced with the other metadata structures to look for discrepancies. Should any errors be found, an error code is returned to userspace, which in the old days would require the administrator to take the filesystem offline and repair it. I've hidden the new online scrubber behind CONFIG_XFS_DEBUG to keep it disabled by default. Last comes the online *repair* functionality, which largely uses the redundancy between the new reverse-mapping feature introduced in 4.8 and the existing storage space records (bno, cnt, ino, fino, and bmap) to reconstruct primary metadata from the secondary, or secondary metadata from the primaries. That's right, we can regrow (some) of the XFS metadata even if parts of the filesystem go bad! Should the kernel succeed, it is not necessary to take the filesystem offline for repair. Finally, there's a patch that uses one of the new scrub features to prevent mount-time deadlocks if the refcountbt is corrupt. If you're going to start using this mess, you probably ought to just pull from my github trees. The kernel patches[1] should apply against 4.10-rc4. xfsprogs[2] and xfstests[3] can be found in their usual places. The patches have survived all of the new tests in [3] that try to fuzz every field in every data structure on disk, which has shaken out several bugs in the scrubber and in other parts of XFS. This is an extraordinary way to eat your data. 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
