Btrfs: adjust btrfs_discard_extent() return errors and trimmed bytes

Callers of btrfs_discard_extent() should check if we are mounted with -o discard,
as we want to make fitrim to work even the fs is not mounted with -o discard.
Also we should use REQ_DISCARD to map the free extent to get a full mapping,
last we only return errors if
1. the error is not a EOPNOTSUPP
2. no device supports discard

Signed-off-by: Li Dongyang <lidongyang@novell.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

3 files changed, 31 insertions, 19 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 9e21176cdf57..a18b7bc2b22c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2229,7 +2229,7 @@ u64 btrfs_account_ro_block_groups_free_space(struct btrfs_space_info *sinfo);
 int btrfs_error_unpin_extent_range(struct btrfs_root *root,
                                    u64 start, u64 end);
 int btrfs_error_discard_extent(struct btrfs_root *root, u64 bytenr,
-                               u64 num_bytes);
+                               u64 num_bytes, u64 *actual_bytes);
 int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root, u64 type);
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 125639ddaffe..8ecc5419d8b6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3054,7 +3054,10 @@ static int btrfs_destroy_pinned_extent(struct btrfs_root *root,
                         break;
 
                 /* opt_discard */
-                ret = btrfs_error_discard_extent(root, start, end + 1 - start);
+                if (btrfs_test_opt(root, DISCARD))
+                        ret = btrfs_error_discard_extent(root, start,
+                                                         end + 1 - start,
+                                                         NULL);
 
                 clear_extent_dirty(unpin, start, end, GFP_NOFS);
                 btrfs_error_unpin_extent_range(root, start, end);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0671f5b77eb8..e990d2d1ba4a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1738,39 +1738,45 @@ static int remove_extent_backref(struct btrfs_trans_handle *trans,
         return ret;
 }
 
-static void btrfs_issue_discard(struct block_device *bdev,
+static int btrfs_issue_discard(struct block_device *bdev,
                                 u64 start, u64 len)
 {
-        blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_NOFS, 0);
+        return blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_NOFS, 0);
 }
 
 static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
-                                u64 num_bytes)
+                                u64 num_bytes, u64 *actual_bytes)
 {
         int ret;
-        u64 map_length = num_bytes;
+        u64 discarded_bytes = 0;
         struct btrfs_multi_bio *multi = NULL;
 
-        if (!btrfs_test_opt(root, DISCARD))
-                return 0;
 
         /* Tell the block device(s) that the sectors can be discarded */
-        ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
-                              bytenr, &map_length, &multi, 0);
+        ret = btrfs_map_block(&root->fs_info->mapping_tree, REQ_DISCARD,
+                              bytenr, &num_bytes, &multi, 0);
         if (!ret) {
                 struct btrfs_bio_stripe *stripe = multi->stripes;
                 int i;
 
-                if (map_length > num_bytes)
-                        map_length = num_bytes;
 
                 for (i = 0; i < multi->num_stripes; i++, stripe++) {
-                        btrfs_issue_discard(stripe->dev->bdev,
-                                            stripe->physical,
-                                            map_length);
+                        ret = btrfs_issue_discard(stripe->dev->bdev,
+                                                  stripe->physical,
+                                                  stripe->length);
+                        if (!ret)
+                                discarded_bytes += stripe->length;
+                        else if (ret != -EOPNOTSUPP)
+                                break;
                 }
                 kfree(multi);
         }
+        if (discarded_bytes && ret == -EOPNOTSUPP)
+                ret = 0;
+
+        if (actual_bytes)
+                *actual_bytes = discarded_bytes;
+
 
         return ret;
 }
@@ -4371,7 +4377,9 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
                 if (ret)
                         break;
 
-                ret = btrfs_discard_extent(root, start, end + 1 - start);
+                if (btrfs_test_opt(root, DISCARD))
+                        ret = btrfs_discard_extent(root, start,
+                                                   end + 1 - start, NULL);
 
                 clear_extent_dirty(unpin, start, end, GFP_NOFS);
                 unpin_extent_range(root, start, end);
@@ -5427,7 +5435,8 @@ int btrfs_free_reserved_extent(struct btrfs_root *root, u64 start, u64 len)
                 return -ENOSPC;
         }
 
-        ret = btrfs_discard_extent(root, start, len);
+        if (btrfs_test_opt(root, DISCARD))
+                ret = btrfs_discard_extent(root, start, len, NULL);
 
         btrfs_add_free_space(cache, start, len);
         btrfs_update_reserved_bytes(cache, len, 0, 1);
@@ -8765,7 +8774,7 @@ int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
 }
 
 int btrfs_error_discard_extent(struct btrfs_root *root, u64 bytenr,
-                               u64 num_bytes)
+                               u64 num_bytes, u64 *actual_bytes)
 {
-        return btrfs_discard_extent(root, bytenr, num_bytes);
+        return btrfs_discard_extent(root, bytenr, num_bytes, actual_bytes);
 }