[PATCH RFC 09/10] btrfs-progs: mkfs/sprout: introduce a helper to remove empty system chunks from seed device

[Qu Wenruo <wqu@suse.com>]

Even if an empty system chunk is still in sys_chunk_array, kernel will
reject the mount.

So here we introduce the helper to do the removal, by iterating through
all block groups, and remove the block group if it's a system chunk and
contains stripe which points to the seed device.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 mkfs/sprout.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/mkfs/sprout.c b/mkfs/sprout.c
index 38d80d789084..049098872d3e 100644
--- a/mkfs/sprout.c
+++ b/mkfs/sprout.c
@@ -241,3 +241,56 @@ static int sprout_relocate_chunk_tree(struct btrfs_trans_handle *trans)
 	btrfs_release_path(&path);
 	return ret;
 }
+
+static int sprout_remove_seed_sys_chunk(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *bg;
+	struct btrfs_device *seed_dev;
+	int ret;
+
+	/* We should have exacly one seed device */
+	ASSERT(fs_info->fs_devices->seed);
+	ASSERT(fs_info->fs_devices->seed->devices.next ==
+	       fs_info->fs_devices->seed->devices.prev);
+	seed_dev = list_entry(fs_info->fs_devices->seed->devices.next,
+			      struct btrfs_device, dev_list);
+	bg = btrfs_lookup_first_block_group(fs_info, 0);
+	while (bg) {
+		const u64 cur = bg->start + bg->length;
+
+		struct cache_extent *ce;
+		struct map_lookup *map;
+		bool delete = false;
+		int i;
+
+		if (!(bg->flags & BTRFS_BLOCK_GROUP_SYSTEM))
+			goto next;
+
+		ce = search_cache_extent(&fs_info->mapping_tree.cache_tree,
+					 bg->start);
+		if (!ce) {
+			/* No chunk map for an bg, a big problem */
+			error("no chunk map for block group at %llu", bg->start);
+			return -EUCLEAN;
+		}
+		map = container_of(ce, struct map_lookup, ce);
+
+		for (i = 0; i < map->num_stripes; i++) {
+			if (map->stripes[i].dev == seed_dev) {
+				delete = true;
+				break;
+			}
+		}
+		if (!delete)
+			goto next;
+
+		ret = btrfs_remove_block_group(trans, bg->start, bg->length);
+		if (ret < 0)
+			return ret;
+next:
+		/* Has to using @cur, as the current bg may has been deleted */
+		bg = btrfs_lookup_first_block_group(fs_info, cur);
+	}
+	return 0;
+}
-- 
2.35.1