There are quite a lot btrfs extent tree corruption report in the mail list. Since btrfs will do mount time block group item search, one corrupted leaf containing block group item will prevent the whole fs to be mounted.
This patchset will try to address the problem by introducing a new mount option, "rescue=skipbg", as a last-resort rescue. With "rescue=skipbg", the whole extent tree will be skipped if we hit some problems at mount time. This brings some side effect that for super large fs, the mount time can be hugely reduced by this mount option. Of course this option will have a lot of restriction to prevent further screwing up the fs, including: - Permanent RO No remount rw is allowed - No dirty log Either clean the log or use rescue=no_log_replay mount option This "rescue=skipbg" has some advantage compared to user space tool like "btrfs-restore": - Unified recovery tool User can use any tool they're familiar with, as long as the kernel doesn't panic. - More info for subvolume. "btrfs subv list" can work now! Also move the following mount options to "rescue=" group: - nologreplay to rescue=nologreplay - usebackuproot to rescue=usebackuproot Old options are still available for compatibility purpose, but they are deprecated in favor of new 'rescue=' super option. Different rescue sub options can be separated by ':', like: "rescue=nologreplay:skipbg:usebackuproot". Or the traditional but longer way like: "rescue=nologreplay,rescue=skipbg" The separation character is chosen by: - No conflicts with existing character Especially no conflict with ','. - No extra escaping/quota Original plan is ';', but since it'll be interpreted by bash, it's changed to current ':'. Changelog: v2: - Introduce 'rescue=' super option. - Rename original 'usebackuproot' and 'nologreplay'. It at least makes my vim spell check happier. - Remove 'recovery' mount option. As its successor is now deprecated, not need to keep the predecessor. v2.1: - Rebase to v5.1-rc4. - Fix the typos in the cover letter. v3: - Rebased to v5.2-rc2. - Update commit message to include an example for "rescue=" options. - Remove unnecessary exclusion of super blocks spaces and block group ro. This seems to cause incorrect df output. v4: - Rebased to v5.3-rc7 Minor conflicts due to some function name and structure change. - Keep the old 'recovery' mount option - Keep the old 'usebackuproot' and 'nologreplay' naming for 'rescue=' mount options So just append 'rescue=' to existing mount option. Qu Wenruo (2): btrfs: Introduce "rescue=" mount option btrfs: Introduce new mount option to skip block group items scan fs/btrfs/ctree.h | 1 + fs/btrfs/disk-io.c | 29 ++++++++++-- fs/btrfs/extent-tree.c | 50 ++++++++++++++++++++ fs/btrfs/super.c | 102 +++++++++++++++++++++++++++++++++++++---- fs/btrfs/volumes.c | 7 +++ 5 files changed, 177 insertions(+), 12 deletions(-) -- 2.23.0
