Btrfs: detect wether a device supports discard

We have a problem where if a user specifies discard but doesn't actually support
it we will return EOPNOTSUPP from btrfs_discard_extent.  This is a problem
because this gets called (in a fashion) from the tree log recovery code, which
has a nice little BUG_ON(ret) after it, which causes us to fail the tree log
replay.  So instead detect wether our devices support discard when we're adding
them and then don't issue discards if we know that the device doesn't support
it.  And just for good measure set ret = 0 in btrfs_issue_discard just in case
we still get EOPNOTSUPP so we don't screw anybody up like this again.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 66bac226944e..059dfa048cc0 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1782,6 +1782,9 @@ static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
 
 
                 for (i = 0; i < multi->num_stripes; i++, stripe++) {
+                        if (!stripe->dev->can_discard)
+                                continue;
+
                         ret = btrfs_issue_discard(stripe->dev->bdev,
                                                   stripe->physical,
                                                   stripe->length);
@@ -1789,11 +1792,16 @@ static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
                                 discarded_bytes += stripe->length;
                         else if (ret != -EOPNOTSUPP)
                                 break;
+
+                        /*
+                         * Just in case we get back EOPNOTSUPP for some reason,
+                         * just ignore the return value so we don't screw up
+                         * people calling discard_extent.
+                         */
+                        ret = 0;
                 }
                 kfree(multi);
         }
-        if (discarded_bytes && ret == -EOPNOTSUPP)
-                ret = 0;
 
         if (actual_bytes)
                 *actual_bytes = discarded_bytes;