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>
---
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
--
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