On 7/25/13 12:29 PM, Anand Jain wrote:
> There is a very less chance that all the copies of SB
> on the disk is zeroed unintentionally. unless device
> is removed, so this fix will ensure all copies on the
> disk is zeroed when the disk is intentionally removed.
>
> reproducer:
> -------------------
> btrfs dev del /dev/sdc /btrfs
> echo $?
> 0
> umount /btrfs
> btrfs fi show
> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c
> Total devices 1 FS bytes used 28.00KiB
> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb
Great, so dev del makes it unfindable . . .
> ./btrfs-select-super -s 1 /dev/sdc
> using SB copy 1, bytenr 67108864
Now you use a rescue tool to resurrect the fs from a backup
superblock. And:
> btrfs fi show
> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c
> Total devices 1 FS bytes used 28.00KiB
> devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG
> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb
Ok, now it's findable. Isn't that exactly how this should behave?
What is wrong about this?
> mount /dev/sdc /btrfs
> btrfs fi show --kernel
> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c mounted: /btrfs
> Group profile: metadata: single data: single
> Total devices 1 FS bytes used 28.00KiB
> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb
Oh good, you could bring it back after a potential administrative error,
using a recovery tool (btrfs-select-super)! Isn't that a good thing?
IOWS: what does this change actually fix?
-Eric
> ---------------------
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> fs/btrfs/volumes.c | 30 ++++++++++++++++++++++++++++++
> 1 files changed, 30 insertions(+), 0 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 557a743..090f57c 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1641,12 +1641,42 @@ int btrfs_rm_device(struct btrfs_root *root, char
> *device_path)
> * remove it from the devices list and zero out the old super
> */
> if (clear_super && disk_super) {
> + u64 bytenr;
> + int i;
> +
> /* make sure this device isn't detected as part of
> * the FS anymore
> */
> memset(&disk_super->magic, 0, sizeof(disk_super->magic));
> set_buffer_dirty(bh);
> sync_dirty_buffer(bh);
> +
> + /* clear the mirror copies of super block on the disk
> + * being removed, 0th copy is been taken care above and
> + * the below would take of the rest
> + */
> + for (i = 1; i < BTRFS_SUPER_MIRROR_MAX; i++) {
> + brelse(bh);
> + bytenr = btrfs_sb_offset(i);
> + if (bytenr + BTRFS_SUPER_INFO_SIZE >=
> + i_size_read(bdev->bd_inode))
> + break;
> + bh = __bread(bdev, bytenr / 4096,
> + BTRFS_SUPER_INFO_SIZE);
> + if (!bh)
> + continue;
> +
> + disk_super = (struct btrfs_super_block *)bh->b_data;
> +
> + if (btrfs_super_bytenr(disk_super) != bytenr ||
> + btrfs_super_magic(disk_super) != BTRFS_MAGIC) {
> + continue;
> + }
> + memset(&disk_super->magic, 0,
> + sizeof(disk_super->magic));
> + set_buffer_dirty(bh);
> + sync_dirty_buffer(bh);
> + }
> }
>
> ret = 0;
>
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