From: Anand Jain Date: Wed, 20 Sep 2023 21:51:13 +0000 (+0800) Subject: btrfs: reject devices with CHANGING_FSID_V2 X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=197a9ecee68aa7706dea47b6dff8d2edbfb214f0;p=linux.git btrfs: reject devices with CHANGING_FSID_V2 The BTRFS_SUPER_FLAG_CHANGING_FSID_V2 flag indicates a transient state where the device in the userspace btrfstune -m|-M operation failed to complete changing the fsid. This flag makes the kernel to automatically determine the other partner devices to which a given device can be associated, based on the fsid, metadata_uuid and generation values. btrfstune -m|M feature is especially useful in virtual cloud setups, where compute instances (disk images) are quickly copied, fsid changed, and launched. Given numerous disk images with the same metadata_uuid but different fsid, there's no clear way a device can be correctly assembled with the proper partners when the CHANGING_FSID_V2 flag is set. So, the disk could be assembled incorrectly, as in the example below: Before this patch: Consider the following two filesystems: /dev/loop[2-3] are raw copies of /dev/loop[0-1] and the btrsftune -m operation fails. In this scenario, as the /dev/loop0's fsid change is interrupted, and the CHANGING_FSID_V2 flag is set as shown below. $ p="device|devid|^metadata_uuid|^fsid|^incom|^generation|^flags" $ btrfs inspect dump-super /dev/loop0 | egrep '$p' superblock: bytenr=65536, device=/dev/loop0 flags 0x1000000001 fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b generation 9 num_devices 2 incompat_flags 0x741 dev_item.devid 1 $ btrfs inspect dump-super /dev/loop1 | egrep '$p' superblock: bytenr=65536, device=/dev/loop1 flags 0x1 fsid 11d2af4d-1b71-45a9-83f6-f2100766939d metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b generation 10 num_devices 2 incompat_flags 0x741 dev_item.devid 2 $ btrfs inspect dump-super /dev/loop2 | egrep '$p' superblock: bytenr=65536, device=/dev/loop2 flags 0x1 fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b generation 8 num_devices 2 incompat_flags 0x741 dev_item.devid 1 $ btrfs inspect dump-super /dev/loop3 | egrep '$p' superblock: bytenr=65536, device=/dev/loop3 flags 0x1 fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b generation 8 num_devices 2 incompat_flags 0x741 dev_item.devid 2 It is normal that some devices aren't instantly discovered during system boot or iSCSI discovery. The controlled scan below demonstrates this. $ btrfs device scan --forget $ btrfs device scan /dev/loop0 Scanning for btrfs filesystems on '/dev/loop0' $ mount /dev/loop3 /btrfs $ btrfs filesystem show -m Label: none uuid: 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 Total devices 2 FS bytes used 144.00KiB devid 1 size 300.00MiB used 48.00MiB path /dev/loop0 devid 2 size 300.00MiB used 40.00MiB path /dev/loop3 /dev/loop0 and /dev/loop3 are incorrectly partnered. This kernel patch removes functions and code connected to the CHANGING_FSID_V2 flag. With this patch, now devices with the CHANGING_FSID_V2 flag are rejected. And its partner will fail to mount with the extra -o degraded option. The check is removed from open_ctree(), devices are rejected during scanning which in turn fails the mount. Signed-off-by: Anand Jain Reviewed-by: David Sterba Signed-off-by: David Sterba --- diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index a55acab37a51a..a970da7263b39 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -3172,7 +3172,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device u32 nodesize; u32 stripesize; u64 generation; - u64 features; u16 csum_type; struct btrfs_super_block *disk_super; struct btrfs_fs_info *fs_info = btrfs_sb(sb); @@ -3254,15 +3253,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device disk_super = fs_info->super_copy; - - features = btrfs_super_flags(disk_super); - if (features & BTRFS_SUPER_FLAG_CHANGING_FSID_V2) { - features &= ~BTRFS_SUPER_FLAG_CHANGING_FSID_V2; - btrfs_set_super_flags(disk_super, features); - btrfs_info(fs_info, - "found metadata UUID change in progress flag, clearing"); - } - memcpy(fs_info->super_for_commit, fs_info->super_copy, sizeof(*fs_info->super_for_commit)); diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index bc8d46cbc7c59..647db23ad8e65 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -791,6 +791,13 @@ static noinline struct btrfs_device *device_list_add(const char *path, bool fsid_change_in_progress = (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_CHANGING_FSID_V2); + if (fsid_change_in_progress) { + btrfs_err(NULL, +"device %s has incomplete metadata_uuid change, please use btrfstune to complete", + path); + return ERR_PTR(-EAGAIN); + } + error = lookup_bdev(path, &path_devt); if (error) { btrfs_err(NULL, "failed to lookup block device for path %s: %d",