Hi all, To prepare the XFS community and potential patch reviewers for the upstream submission of the online fsck feature, I decided to write a document capturing the broader picture behind the online repair development effort. The document begins by defining the problems that online fsck aims to solve and outlining specific use cases for the functionality. Using that as a base, the rest of the design document presents the high level algorithms that fulfill the goals set out at the start and the interactions between the large pieces of the system. Case studies round out the design documentation by adding the details of exactly how specific parts of the online fsck code integrate the algorithms with the filesystem. The goal of this effort is to help the XFS community understand how the gigantic online repair patchset works. The questions I submit to the community reviewers are: 1. As you read the design doc (and later the code), do you feel that you understand what's going on well enough to try to fix a bug if you found one? 2. What sorts of interactions between systems (or between scrub and the rest of the kernel) am I missing? 3. Do you feel confident enough in the implementation as it is now that the benefits of merging the feature (as EXPERIMENTAL) outweigh any potential disruptions to XFS at large? 4. Are there problematic interactions between subsystems that ought to be cleared up before merging? I intend to commit this document to the kernel's documentation directory around the time we start merging the patchset, albeit without the links to git.kernel.org. A much more readable version of this is posted at: https://djwong.org/docs/xfs-online-fsck-design/ v2: add missing sections about: all the in-kernel data structures and new apis that the scrub and repair functions use; how xattrs and directories are checked; how space btree records are checked; and add more details to the parts where all these bits tie together. Proofread for verb tense inconsistencies and eliminate vague 'we' usage. Move all the discussion of what we can do with pageable kernel memory into a single source file and section. Document where log incompat feature locks fit into the locking model. If you're going to start using this mess, you probably ought to just pull from my git trees, which are linked below. This is an extraordinary way to destroy everything. Enjoy! Comments and questions are, as always, welcome. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=online-fsck-design --- Documentation/filesystems/index.rst | 1 .../filesystems/xfs-online-fsck-design.rst | 4979 ++++++++++++++++++++ .../filesystems/xfs-self-describing-metadata.rst | 1 3 files changed, 4981 insertions(+) create mode 100644 Documentation/filesystems/xfs-online-fsck-design.rst
