[PATCH v4 2/9] btrfs: introduce a helper to locate an extent item

Qu Wenruo
2022-03-11T07:39:15Z

The new helper, find_first_extent_item(), will locate an extent item
(either EXTENT_ITEM or METADATA_ITEM) which covers *ANY* byte of the
search range.

This helper will later be used to refactor scrub code.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/scrub.c | 108 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 108 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index c2bf7bbcee67..ce33cd4aa54d 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2882,6 +2882,114 @@ static void scrub_parity_put(struct scrub_parity *sparity)
scrub_parity_check_and_repair(sparity);
}

+/*
+ * Return 0 if the extent item range covers any byte of the range.
+ * Return <0 if the extent item is before @search_start.
+ * Return >0 if the extent item is after @start_start + @search_len.
+ */
+static int compare_extent_item_range(struct btrfs_path *path,
+ u64 search_start, u64 search_len)
+{
+ struct btrfs_fs_info *fs_info = path->nodes[0]->fs_info;
+ u64 len;
+ struct btrfs_key key;
+
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ ASSERT(key.type == BTRFS_EXTENT_ITEM_KEY ||
+ key.type == BTRFS_METADATA_ITEM_KEY);
+ if (key.type == BTRFS_METADATA_ITEM_KEY)
+ len = fs_info->nodesize;
+ else
+ len = key.offset;
+
+ if (key.objectid + len <= search_start)
+ return -1;
+ if (key.objectid >= search_start + search_len)
+ return 1;
+ return 0;
+}
+
+/*
+ * Helper to locate one extent item which covers any byte in range
+ * [@search_start, @search_start + @search_length)
+ *
+ * If the path is not initialized, we will initialize the search by doing
+ * a btrfs_search_slot().
+ * If the path is already initialized, we will use the path as the initial
+ * slot, to avoid duplicated btrfs_search_slot() calls.
+ *
+ * NOTE: If an extent item starts before @search_start, we will still
+ * return the extent item. This is for data extent crossing stripe boundary.
+ *
+ * Return 0 if we found such extent item, and @path will point to the
+ * extent item.
+ * Return >0 if no such extent item can be found, and @path will be released.
+ * Return <0 if hit fatal error, and @path will be released.
+ */
+static int find_first_extent_item(struct btrfs_root *extent_root,
+ struct btrfs_path *path,
+ u64 search_start, u64 search_len)
+{
+ struct btrfs_fs_info *fs_info = extent_root->fs_info;
+ struct btrfs_key key;
+ int ret;
+
+ /* Continue using the existing path */
+ if (path->nodes[0])
+ goto search_forward;
+
+ if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
+ key.type = BTRFS_METADATA_ITEM_KEY;
+ else
+ key.type = BTRFS_EXTENT_ITEM_KEY;
+ key.objectid = search_start;
+ key.offset = (u64)-1;
+
+ ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
+ if (ret < 0)
+ return ret;
+
+ ASSERT(ret > 0);
+ /*
+ * Here we intentionally pass 0 as @min_objectid, as there could be
+ * an extent item starting before @search_start.
+ */
+ ret = btrfs_previous_extent_item(extent_root, path, 0);
+ if (ret < 0)
+ return ret;
+ /*
+ * No matter whether we have found an extent item, the next loop will
+ * properly do every check on the key.
+ */
+search_forward:
+ while (true) {
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ if (key.objectid >= search_start + search_len)
+ break;
+ if (key.type != BTRFS_METADATA_ITEM_KEY &&
+ key.type != BTRFS_EXTENT_ITEM_KEY)
+ goto next;
+
+ ret = compare_extent_item_range(path, search_start, search_len);
+ if (ret == 0)
+ return ret;
+ if (ret > 0)
+ break;
+next:
+ path->slots[0]++;
+ if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+ ret = btrfs_next_leaf(extent_root, path);
+ if (ret) {
+ /* Either no more item or fatal error */
+ btrfs_release_path(path);
+ return ret;
+ }
+ }
+ }
+ btrfs_release_path(path);
+ return 1;
+}
+
static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
struct map_lookup *map,
struct btrfs_device *sdev,
--
2.35.1