btrfs: allow balancing to dup with multi-device

commit 88be159c905a2b4f6d59afa352bef410afb6af02 upstream.

Currently, we don't allow the user to try and rebalance to a dup profile
on a multi-device filesystem.  In most cases, this is a perfectly sensible
restriction as raid1 uses the same amount of space and provides better
protection.

However, when reshaping a multi-device filesystem down to a single device
filesystem, this requires the user to convert metadata and system chunks
to single profile before deleting devices, and then convert again to dup,
which leaves a period of time where metadata integrity is reduced.

This patch removes the single-device-only restriction from converting to
dup profile to remove this potential data integrity reduction.

Signed-off-by: Austin S. Hemmelgarn <ahferroin7@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index adb5f697a9634e5741360c4cc52ee7e935147e50..89c2aabaea2d977027418d7351478774ce462d8e 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3699,10 +3699,8 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
                num_devices--;
        }
        btrfs_dev_replace_unlock(&fs_info->dev_replace);
-       allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
-       if (num_devices == 1)
-               allowed |= BTRFS_BLOCK_GROUP_DUP;
-       else if (num_devices > 1)
+       allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE | BTRFS_BLOCK_GROUP_DUP;
+       if (num_devices > 1)
                allowed |= (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1);
        if (num_devices > 2)
                allowed |= BTRFS_BLOCK_GROUP_RAID5;