[PATCH v3 1/2] btrfs: implement partial deletion of RAID stripe extents

[Johannes Thumshirn <jth@kernel.org>]

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

In our CI system, the RAID stripe tree configuration sometimes fails with
the following ASSERT():

 assertion failed: found_start >= start && found_end <= end, in fs/btrfs/raid-stripe-tree.c:64

This ASSERT()ion triggers, because for the initial design of RAID
stripe-tree, I had the "one ordered-extent equals one bio" rule of zoned
btrfs in mind.

But for a RAID stripe-tree based system, that is not hosted on a zoned
storage device, but on a regular device this rule doesn't apply.

So in case the range we want to delete starts in the middle of the
previous item, grab the item and "truncate" it's length. That is, clone
the item, subtract the deleted portion from the key's offset, delete the
old item and insert the new one.

In case the range to delete ends in the middle of an item, we have to
adjust both the item's key as well as the stripe extents and then
re-insert the modified clone into the tree after deleting the old stripe
extent.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/raid-stripe-tree.c | 85 +++++++++++++++++++++++++++++++++++--
 1 file changed, 81 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
index 41970bbdb05f..40cc0a392be2 100644
--- a/fs/btrfs/raid-stripe-tree.c
+++ b/fs/btrfs/raid-stripe-tree.c
@@ -13,6 +13,54 @@
 #include "volumes.h"
 #include "print-tree.h"
 
+static int btrfs_partially_delete_raid_extent(struct btrfs_trans_handle *trans,
+					      struct btrfs_path *path,
+					      struct btrfs_key *oldkey,
+					      u64 newlen, u64 frontpad)
+{
+	struct btrfs_root *stripe_root = trans->fs_info->stripe_root;
+	struct btrfs_stripe_extent *extent, *new;
+	struct extent_buffer *leaf = path->nodes[0];
+	int slot = path->slots[0];
+	const size_t item_size = btrfs_item_size(leaf, slot);
+	struct btrfs_key newkey;
+	int ret;
+	int i;
+
+	new = kzalloc(item_size, GFP_NOFS);
+	if (!new)
+		return -ENOMEM;
+
+	memcpy(&newkey, oldkey, sizeof(struct btrfs_key));
+	newkey.objectid += frontpad;
+	newkey.offset -= newlen;
+
+	extent = btrfs_item_ptr(leaf, slot, struct btrfs_stripe_extent);
+
+	for (i = 0; i < btrfs_num_raid_stripes(item_size); i++) {
+		u64 devid;
+		u64 phys;
+
+		devid = btrfs_raid_stride_devid(leaf, &extent->strides[i]);
+		btrfs_set_stack_raid_stride_devid(&new->strides[i], devid);
+
+		phys = btrfs_raid_stride_physical(leaf, &extent->strides[i]);
+		phys += frontpad;
+		btrfs_set_stack_raid_stride_physical(&new->strides[i], phys);
+	}
+
+	ret = btrfs_del_item(trans, stripe_root, path);
+	if (ret)
+		goto out;
+
+	btrfs_release_path(path);
+	ret = btrfs_insert_item(trans, stripe_root, &newkey, new, item_size);
+
+ out:
+	kfree(new);
+	return ret;
+}
+
 int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 length)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
@@ -43,9 +91,8 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
 			break;
 		if (ret > 0) {
 			ret = 0;
-			if (path->slots[0] == 0)
-				break;
-			path->slots[0]--;
+			if (path->slots[0] > 0)
+				path->slots[0]--;
 		}
 
 		leaf = path->nodes[0];
@@ -61,7 +108,37 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
 		trace_btrfs_raid_extent_delete(fs_info, start, end,
 					       found_start, found_end);
 
-		ASSERT(found_start >= start && found_end <= end);
+		/*
+		 * The stripe extent starts before the range we want to delete:
+		 *
+		 * |--- RAID Stripe Extent ---|
+		 * |--- keep  ---|--- drop ---|
+		 *
+		 * This means we have to duplicate the tree item, truncate the
+		 * length to the new size and then re-insert the item.
+		 */
+		if (found_start < start) {
+			ret = btrfs_partially_delete_raid_extent(trans, path, &key,
+							start - found_start, 0);
+			break;
+		}
+
+		/*
+		 * The stripe extent ends after the range we want to delete:
+		 *
+		 * |--- RAID Stripe Extent ---|
+		 * |--- drop  ---|--- keep ---|
+		 * This means we have to duplicate the tree item, truncate the
+		 * length to the new size and then re-insert the item.
+		 */
+		if (found_end > end) {
+			u64 diff = found_end - end;
+
+			ret = btrfs_partially_delete_raid_extent(trans, path, &key,
+								 diff, diff);
+			break;
+		}
+
 		ret = btrfs_del_item(trans, stripe_root, path);
 		if (ret)
 			break;
-- 
2.43.0