[PATCH v3 06/14] btrfs: fix deletion of a range spanning parts two RAID stripe extents

[Johannes Thumshirn <jth@kernel.org>]

From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

When a user requests the deletion of a range that spans multiple stripe
extents and btrfs_search_slot() returns us the second RAID stripe extent,
we need to pick the previous item and truncate it, if there's still a
range to delete left, move on to the next item.

The following diagram illustrates the operation:

 |--- RAID Stripe Extent ---||--- RAID Stripe Extent ---|
        |--- keep  ---|--- drop ---|

While at it, comment the trivial case of a whole item delete as well.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/raid-stripe-tree.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
index ef76202c3a38460c5a36d7309ac0a616f73b0cc0..7ddc139ae1cf2d4844b1955ed3ecfe1b91f40049 100644
--- a/fs/btrfs/raid-stripe-tree.c
+++ b/fs/btrfs/raid-stripe-tree.c
@@ -99,6 +99,31 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
 		found_end = found_start + key.offset;
 		ret = 0;
 
+		/*
+		 * The stripe extent starts before the range we want to delete,
+		 * but the range spans more than one stripe extent:
+		 *
+		 * |--- RAID Stripe Extent ---||--- RAID Stripe Extent ---|
+		 *        |--- keep  ---|--- drop ---|
+		 *
+		 * This means we have to get the previous item, truncate its
+		 * length and then restart the search.
+		 */
+		if (found_start > start) {
+
+			ret = btrfs_previous_item(stripe_root, path, start,
+						  BTRFS_RAID_STRIPE_KEY);
+			if (ret < 0)
+				break;
+			ret = 0;
+
+			leaf = path->nodes[0];
+			slot = path->slots[0];
+			btrfs_item_key_to_cpu(leaf, &key, slot);
+			found_start = key.objectid;
+			found_end = found_start + key.offset;
+		}
+
 		if (key.type != BTRFS_RAID_STRIPE_KEY)
 			break;
 
@@ -152,6 +177,9 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
 			break;
 		}
 
+		/*
+		 * Finally we can delete the whole item, no more special cases.
+		 */
 		ret = btrfs_del_item(trans, stripe_root, path);
 		if (ret)
 			break;

-- 
2.43.0