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> --- v1->v2: zero only the magic of the alien superblock, instead of whole of superblock. And comments updated. Thanks. utils.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/utils.c b/utils.c index 715bab0ebfb5..4e7964962d0e 100644 --- a/utils.c +++ b/utils.c @@ -367,6 +367,42 @@ int btrfs_prepare_device(int fd, const char *file, u64 *block_count_ret, return 1; } + /* + * Check and wipe alien superblock at bytenr beyond the block_count. + */ + 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; + + if (btrfs_sb_offset(i) < block_count) + continue; + + /* Beyond actual disk size */ + if (btrfs_sb_offset(i) >= btrfs_device_size(fd, &st)) + continue; + + /* + * We are reading sperblock at bytenr > block_count, and + * if there is a valid superblock then its an alien + * superblock which should be wiped. + */ + if (btrfs_read_dev_super(fd, disk_super, + btrfs_sb_offset(i), 0)) + continue; + + ret = zero_blocks(fd, btrfs_sb_offset(i) + + offsetof(struct btrfs_super_block, magic), + sizeof(u64)); + 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