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.jain@xxxxxxxxxx>
---
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
--
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