Re: [PATCH 01/10] Btrfs: Fix the problem that the replace destroys the seed filesystem

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 Thanks for nailing down most of the seed related bugs, scratching
 off few from my list.


On 07/24/2014 11:37 AM, Miao Xie wrote:
The seed filesystem was destroyed by the device replace, the reproduce
method is:
  # mkfs.btrfs -f <dev0>
  # btrfstune -S 1 <dev0>
  # mount <dev0> <mnt>
  # btrfs device add <dev1> <mnt>
  # umount <mnt>
  # mount <dev1> <mnt>
  # btrfs replace start -f <dev0> <dev2> <mnt>
  # umount <mnt>
  # mount <dev0> <mnt>

It is because we erase the super block on the seed device. It is wrong,
we should not change anything on the seed device.

nice fix.

Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>

Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx>
---
  fs/btrfs/volumes.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2776070f..19188df 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1853,8 +1853,12 @@ void btrfs_rm_dev_replace_srcdev(struct btrfs_fs_info *fs_info,
  	if (srcdev->bdev) {
  		fs_info->fs_devices->open_devices--;

-		/* zero out the old super */
-		btrfs_scratch_superblock(srcdev);
+		/*
+		 * zero out the old super if it is not writable
+		 * (e.g. seed device)
+		 */
+		if (srcdev->writeable)
+			btrfs_scratch_superblock(srcdev);
  	}

  	call_rcu(&srcdev->rcu, free_device);

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