During the mkfs.btrfs -b <blockcount> btrfs_prepare_device() zeros all the superblock bytenr locations only if the bytenr is below the blockcount. The problem with this is that if the BTRFS is recreated with a smaller size then we will leave the stale superblock in the disk which shall confuse the recovery. As shown in the test case below.
mkfs.btrfs -qf /dev/mapper/vg-lv mkfs.btrfs -qf -b1G /dev/mapper/vg-lv btrfs in dump-super -a /dev/mapper/vg-lv | grep '.fsid|superblock:' superblock: bytenr=65536, device=/dev/mapper/vg-lv dev_item.fsid ebc67d01-7fc5-43f0-90b4-d1925002551e [match] superblock: bytenr=67108864, device=/dev/mapper/vg-lv dev_item.fsid ebc67d01-7fc5-43f0-90b4-d1925002551e [match] superblock: bytenr=274877906944, device=/dev/mapper/vg-lv dev_item.fsid b97a9206-593b-4933-a424-c6a6ee23fe7c [match] So if we find a valid superblock zero it even if it's beyond the blockcount. Signed-off-by: Anand Jain <anand.j...@oracle.com> --- utils.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/utils.c b/utils.c index e9cb3a82fda6..6a9408b06e73 100644 --- a/utils.c +++ b/utils.c @@ -365,6 +365,41 @@ int btrfs_prepare_device(int fd, const char *file, u64 *block_count_ret, return 1; } + /* + * Check for the BTRFS SB copies up until btrfs_device_size() and zero + * it. So that kernel (or user for the manual recovery) don't have to + * confuse with the stale SB copy during recovery. + */ + if (block_count != btrfs_device_size(fd, &st)) { + for (i = 1; i < BTRFS_SUPER_MIRROR_MAX; i++) { + struct btrfs_super_block *disk_super; + char buf[BTRFS_SUPER_INFO_SIZE]; + disk_super = (struct btrfs_super_block *)buf; + + /* Already zeroed above */ + if (btrfs_sb_offset(i) < block_count) + continue; + + /* Beyond actual disk size */ + if (btrfs_sb_offset(i) >= btrfs_device_size(fd, &st)) + continue; + + /* Does not contain any stale SB */ + if (btrfs_read_dev_super(fd, disk_super, + btrfs_sb_offset(i), 0)) + continue; + + ret = zero_dev_clamped(fd, btrfs_sb_offset(i), + BTRFS_SUPER_INFO_SIZE, + btrfs_device_size(fd, &st)); + if (ret < 0) { + error("failed to zero device '%s' bytenr %llu: %s", + file, btrfs_sb_offset(i), strerror(-ret)); + return 1; + } + } + } + *block_count_ret = block_count; return 0; } -- 2.7.0 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html