[PATCH v2] btrfs: fix a bogus warning when converting only data or metadata

[Adam Borowski <kilobyte@angband.pl>]

If your filesystem has, eg, data:raid0 metadata:raid1, and you run "btrfs
balance -dconvert=raid1", the meta.target field will be uninitialized.
That's otherwise ok, as it's unused except for this warning.

Thus, let's use the existing set of raid levels for the comparison.

As a side effect, non-convert balances will now nag about data>metadata.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
---
To reproduce:
dd if=/dev/zero bs=1048576 count=1 seek=4095 of=ra
dd if=/dev/zero bs=1048576 count=1 seek=4095 of=rb
mkfs.btrfs ra rb     # defaults to -draid0 -mraid1
losetup -f ra
losetup -f rb
mount /dev/loop0 /mnt/vol1
btrfs balance start -dconvert=raid1 /mnt/vol1


On Tue, Mar 07, 2017 at 12:34:07PM -0800, Liu Bo wrote:
> This looks good, but this also brings another side effect, @bctl would
> also be kept in balance_item which will be used to resume balance in
> case of crash, so it may see a different bctl->meta.target.
>
> So would you please use local varibles for meta.target and data.target?

Okay.

I'm not sure why storing a bogus value that came from userspace and was
uninitialized there (0 in normal use) would be better, but here we go:
v2 doesn't overwrite what we got anymore.

Unrelated: I wonder if the profiles in the warning message shouldn't be
printk'ed as words (akin to ebce0e01), but we don't have a function to do
that, have we?


Meow!

 fs/btrfs/volumes.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3645af2749f8..987f395ddec5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3750,6 +3750,7 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
 		  struct btrfs_ioctl_balance_args *bargs)
 {
 	struct btrfs_fs_info *fs_info = bctl->fs_info;
+	__u64 meta_target, data_target;
 	u64 allowed;
 	int mixed = 0;
 	int ret;
@@ -3846,11 +3847,16 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
 		}
 	} while (read_seqretry(&fs_info->profiles_lock, seq));
 
-	if (btrfs_get_num_tolerated_disk_barrier_failures(bctl->meta.target) <
-		btrfs_get_num_tolerated_disk_barrier_failures(bctl->data.target)) {
+	/* if we're not converting, the target field is uninitialized */
+	meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
+		bctl->meta.target : fs_info->avail_metadata_alloc_bits;
+	data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
+		bctl->data.target : fs_info->avail_data_alloc_bits;
+	if (btrfs_get_num_tolerated_disk_barrier_failures(meta_target) <
+		btrfs_get_num_tolerated_disk_barrier_failures(data_target)) {
 		btrfs_warn(fs_info,
 			   "metadata profile 0x%llx has lower redundancy than data profile 0x%llx",
-			   bctl->meta.target, bctl->data.target);
+			   meta_target, data_target);
 	}
 
 	ret = insert_balance_item(fs_info, bctl);
-- 
2.11.0