Hello, Here is the second posting of the fsid change support for the kernel. For background information you can refer to v1 [0]. The main changes in this version are around the handling of possible split-brain scenarios. I've changed a bit how the userspace code works and now the process is split among 2 transactions. The first one flagging "we are about to change fsid" and once it's persisted on all disks a second one does the actual change. This of course is not enough to guarantee full consistency so I had to extend the device scanning to gracefully handle such cases. I believe I have covered everything but more review will be appreciated.
So patch 1 implements the basic functionality with no split-brain handling whatsoever. Patch 2 is a minor cleanup. Patch 3 deals with a split-brain that can occur if power loss happens during the initial transaction (the one setting the beginning flag). Patch 4 adds some information that is needed in the last 2 patches. Patch 5 handles failure between transaction 1 and transaction 2 and finally patch 6 handles the case of power loss during transaction 1 but for an fs which has already undergone at least one successful fsid change. More details about the exact failure modes are in each respective patch. One thing which could be improved but I ran out of ideas is the naming of the ancillary functions - find_fsid_inprogress and find_fsid_changed. I've actually tested the split-brain handing code with specially crafted images. They will be part of the user-space submissions and I believe I have full coverage for that. [0] https://lore.kernel.org/linux-btrfs/1535531774-29830-1-git-send-email-nbori...@suse.com/ Nikolay Borisov (6): btrfs: Introduce support for FSID change without metadata rewrite btrfs: Remove fsid/metadata_fsid fields from btrfs_info btrfs: Add handling for disk split-brain scenario during fsid change btrfs: Introduce 2 more members to struct btrfs_fs_devices btrfs: Handle one more split-brain scenario during fsid change btrfs: Handle final split-brain possibility during fsid change fs/btrfs/check-integrity.c | 2 +- fs/btrfs/ctree.c | 5 +- fs/btrfs/ctree.h | 10 +- fs/btrfs/disk-io.c | 53 ++++++++--- fs/btrfs/extent-tree.c | 2 +- fs/btrfs/ioctl.c | 2 +- fs/btrfs/super.c | 2 +- fs/btrfs/volumes.c | 196 ++++++++++++++++++++++++++++++++++++---- fs/btrfs/volumes.h | 6 ++ include/trace/events/btrfs.h | 2 +- include/uapi/linux/btrfs.h | 1 + include/uapi/linux/btrfs_tree.h | 1 + 12 files changed, 241 insertions(+), 41 deletions(-) -- 2.7.4
