btrfs: introduce a bitmap based csum range search function

Although we have an existing function, btrfs_lookup_csums_range(), to
find all data checksums for a range, it's based on a btrfs_ordered_sum
list.

For the incoming RAID56 data checksum verification at RMW time, we don't
want to waste time by allocating temporary memory.

So this patch will introduce a new helper, btrfs_lookup_csums_bitmap().
It will use bitmap based result, which will be a perfect fit for later
RAID56 usage.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file-item.c

@@ -527,7 +527,7 @@ blk_status_t btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio, u8 *dst
 	return ret;
 }
 
-int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
+int btrfs_lookup_csums_list(struct btrfs_root *root, u64 start, u64 end,
 			    struct list_head *list, int search_commit,
 			    bool nowait)
 {
@@ -661,6 +661,127 @@ int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
 	return ret;
 }
 
+/*
+ * Do the same work as btrfs_lookup_csums_list(), the difference is in how
+ * we return the result.
+ *
+ * This version will set the corresponding bits in @csum_bitmap to represent
+ * that there is a csum found.
+ * Each bit represents a sector. Thus caller should ensure @csum_buf passed
+ * in is large enough to contain all csums.
+ */
+int btrfs_lookup_csums_bitmap(struct btrfs_root *root, u64 start, u64 end,
+			      u8 *csum_buf, unsigned long *csum_bitmap)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct btrfs_key key;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_csum_item *item;
+	const u64 orig_start = start;
+	int ret;
+
+	ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
+	       IS_ALIGNED(end + 1, fs_info->sectorsize));
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
+	key.type = BTRFS_EXTENT_CSUM_KEY;
+	key.offset = start;
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		goto fail;
+	if (ret > 0 && path->slots[0] > 0) {
+		leaf = path->nodes[0];
+		btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
+
+		/*
+		 * There are two cases we can hit here for the previous csum
+		 * item:
+		 *
+		 *		|<- search range ->|
+		 *	|<- csum item ->|
+		 *
+		 * Or
+		 *				|<- search range ->|
+		 *	|<- csum item ->|
+		 *
+		 * Check if the previous csum item covers the leading part of
+		 * the search range.  If so we have to start from previous csum
+		 * item.
+		 */
+		if (key.objectid == BTRFS_EXTENT_CSUM_OBJECTID &&
+		    key.type == BTRFS_EXTENT_CSUM_KEY) {
+			if (bytes_to_csum_size(fs_info, start - key.offset) <
+			    btrfs_item_size(leaf, path->slots[0] - 1))
+				path->slots[0]--;
+		}
+	}
+
+	while (start <= end) {
+		u64 csum_end;
+
+		leaf = path->nodes[0];
+		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret < 0)
+				goto fail;
+			if (ret > 0)
+				break;
+			leaf = path->nodes[0];
+		}
+
+		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+		if (key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
+		    key.type != BTRFS_EXTENT_CSUM_KEY ||
+		    key.offset > end)
+			break;
+
+		if (key.offset > start)
+			start = key.offset;
+
+		csum_end = key.offset + csum_size_to_bytes(fs_info,
+					btrfs_item_size(leaf, path->slots[0]));
+		if (csum_end <= start) {
+			path->slots[0]++;
+			continue;
+		}
+
+		csum_end = min(csum_end, end + 1);
+		item = btrfs_item_ptr(path->nodes[0], path->slots[0],
+				      struct btrfs_csum_item);
+		while (start < csum_end) {
+			unsigned long offset;
+			size_t size;
+			u8 *csum_dest = csum_buf + bytes_to_csum_size(fs_info,
+						start - orig_start);
+
+			size = min_t(size_t, csum_end - start, end + 1 - start);
+
+			offset = bytes_to_csum_size(fs_info, start - key.offset);
+
+			read_extent_buffer(path->nodes[0], csum_dest,
+					   ((unsigned long)item) + offset,
+					   bytes_to_csum_size(fs_info, size));
+
+			bitmap_set(csum_bitmap,
+				(start - orig_start) >> fs_info->sectorsize_bits,
+				size >> fs_info->sectorsize_bits);
+
+			start += size;
+		}
+		path->slots[0]++;
+	}
+	ret = 0;
+fail:
+	btrfs_free_path(path);
+	return ret;
+}
+
 /*
  * Calculate checksums of the data contained inside a bio.
  *

fs/btrfs/file-item.h

@@ -18,9 +18,11 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
 			   struct btrfs_ordered_sum *sums);
 blk_status_t btrfs_csum_one_bio(struct btrfs_inode *inode, struct bio *bio,
 				u64 offset, bool one_ordered);
-int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
+int btrfs_lookup_csums_list(struct btrfs_root *root, u64 start, u64 end,
 			    struct list_head *list, int search_commit,
 			    bool nowait);
+int btrfs_lookup_csums_bitmap(struct btrfs_root *root, u64 start, u64 end,
+			      u8 *csum_buf, unsigned long *csum_bitmap);
 void btrfs_extent_item_to_extent_map(struct btrfs_inode *inode,
 				     const struct btrfs_path *path,
 				     struct btrfs_file_extent_item *fi,

fs/btrfs/inode.c

@@ -1709,9 +1709,8 @@ static noinline int csum_exist_in_range(struct btrfs_fs_info *fs_info,
 	int ret;
 	LIST_HEAD(list);
 
-	ret = btrfs_lookup_csums_range(csum_root, bytenr,
-				       bytenr + num_bytes - 1, &list, 0,
-				       nowait);
+	ret = btrfs_lookup_csums_list(csum_root, bytenr, bytenr + num_bytes - 1,
+				      &list, 0, nowait);
 	if (ret == 0 && list_empty(&list))
 		return 0;
 

fs/btrfs/relocation.c

@@ -4357,7 +4357,7 @@ int btrfs_reloc_clone_csums(struct btrfs_inode *inode, u64 file_pos, u64 len)
 
 	disk_bytenr = file_pos + inode->index_cnt;
 	csum_root = btrfs_csum_root(fs_info, disk_bytenr);
-	ret = btrfs_lookup_csums_range(csum_root, disk_bytenr,
+	ret = btrfs_lookup_csums_list(csum_root, disk_bytenr,
 				      disk_bytenr + len - 1, &list, 0, false);
 	if (ret)
 		goto out;

fs/btrfs/scrub.c

@@ -3238,7 +3238,7 @@ static int scrub_raid56_data_stripe_for_parity(struct scrub_ctx *sctx,
 		extent_dev = bioc->stripes[0].dev;
 		btrfs_put_bioc(bioc);
 
-		ret = btrfs_lookup_csums_range(csum_root, extent_start,
+		ret = btrfs_lookup_csums_list(csum_root, extent_start,
 					      extent_start + extent_size - 1,
 					      &sctx->csum_list, 1, false);
 		if (ret) {
@@ -3464,7 +3464,7 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
 			    cur_logical;
 
 		if (extent_flags & BTRFS_EXTENT_FLAG_DATA) {
-			ret = btrfs_lookup_csums_range(csum_root, cur_logical,
+			ret = btrfs_lookup_csums_list(csum_root, cur_logical,
 					cur_logical + scrub_len - 1,
 					&sctx->csum_list, 1, false);
 			if (ret)

fs/btrfs/tree-log.c

@@ -826,7 +826,7 @@ static noinline int replay_one_extent(struct btrfs_trans_handle *trans,
 					btrfs_file_extent_num_bytes(eb, item);
 			}
 
-			ret = btrfs_lookup_csums_range(root->log_root,
+			ret = btrfs_lookup_csums_list(root->log_root,
 						csum_start, csum_end - 1,
 						&ordered_sums, 0, false);
 			if (ret)
@@ -4443,7 +4443,7 @@ static noinline int copy_items(struct btrfs_trans_handle *trans,
 
 		csum_root = btrfs_csum_root(trans->fs_info, disk_bytenr);
 		disk_bytenr += extent_offset;
-		ret = btrfs_lookup_csums_range(csum_root, disk_bytenr,
+		ret = btrfs_lookup_csums_list(csum_root, disk_bytenr,
 					      disk_bytenr + extent_num_bytes - 1,
 					      &ordered_sums, 0, false);
 		if (ret)
@@ -4638,8 +4638,7 @@ static int log_extent_csums(struct btrfs_trans_handle *trans,
 
 	/* block start is already adjusted for the file extent offset. */
 	csum_root = btrfs_csum_root(trans->fs_info, em->block_start);
-	ret = btrfs_lookup_csums_range(csum_root,
-				       em->block_start + csum_offset,
+	ret = btrfs_lookup_csums_list(csum_root, em->block_start + csum_offset,
 				      em->block_start + csum_offset +
 				      csum_len - 1, &ordered_sums, 0, false);
 	if (ret)