btrfs-progs: mkfs: discard free space

When we've finished creating a new filesystem, walk the free-space tree and
call discard for what we find - this is the approach that we use with FITRIM
in the kernel.

The ranges that are free but not already discarded are the metadata blocks
that mkfs.btrfs creates with its intermediate transactions.

Pull-request: #1021
Signed-off-by: Mark Harmstone <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: maharmstone

mkfs/main.c

@@ -1291,6 +1291,106 @@ static int parse_inode_flags(const char *option, struct list_head *inode_flags_l
 	return ret;
 }
 
+static int discard_free_space(struct btrfs_fs_info *fs_info, u64 metadata_profile)
+{
+	struct btrfs_root *free_space_root;
+	struct btrfs_path path = { 0 };
+	struct extent_buffer *leaf;
+	int ret;
+	struct btrfs_key key = {
+		.objectid = BTRFS_FREE_SPACE_TREE_OBJECTID,
+		.type = BTRFS_ROOT_ITEM_KEY,
+		.offset = 0,
+	};
+
+	if (!btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
+		return 0;
+
+	/*
+	 * Follow the kernel in not doing discard for RAID5 or 6.
+	 * We don't have to worry about data here, as --rootdir only works
+	 * with single-device filesystems, and the data block groups are
+	 * empty otherwise.
+	 */
+
+	if (metadata_profile & BTRFS_BLOCK_GROUP_RAID56_MASK)
+		return 0;
+
+	free_space_root = btrfs_global_root(fs_info, &key);
+
+	key.objectid = 0;
+	key.type = 0;
+	key.offset = 0;
+
+	ret = btrfs_search_slot(NULL, free_space_root, &key, &path, 0, 0);
+	if (ret < 0)
+		return ret;
+
+	while (true) {
+		leaf = path.nodes[0];
+
+		if (path.slots[0] >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(free_space_root, &path);
+			if (ret)
+				break;
+
+			leaf = path.nodes[0];
+		}
+
+		btrfs_item_key_to_cpu(leaf, &key, path.slots[0]);
+
+		if (key.type == BTRFS_FREE_SPACE_EXTENT_KEY) {
+			ret = discard_logical_range(fs_info, key.objectid, key.offset);
+			if (ret < 0)
+				goto out;
+		} else if (key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
+			int size, nrbits;
+			void *bitmap;
+			unsigned long start_bit, end_bit;
+
+			size = btrfs_item_size(leaf, path.slots[0]);
+			bitmap = malloc(size);
+			if (!bitmap) {
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			read_extent_buffer(leaf, bitmap,
+					   btrfs_item_ptr_offset(leaf, path.slots[0]),
+					   size);
+
+			nrbits = div_u64(key.offset, fs_info->sectorsize);
+			start_bit = find_next_bit_le(bitmap, nrbits, 0);
+
+			while (start_bit < nrbits) {
+				u64 addr, length;
+
+				end_bit = find_next_zero_bit_le(bitmap, nrbits, start_bit);
+				addr = key.objectid + (start_bit * fs_info->sectorsize);
+				length = (end_bit - start_bit) * fs_info->sectorsize;
+
+				ret = discard_logical_range(fs_info, addr, length);
+				if (ret < 0) {
+					free(bitmap);
+					goto out;
+				}
+
+				start_bit = find_next_bit_le(bitmap, nrbits, end_bit);
+			}
+
+			free(bitmap);
+		}
+
+		path.slots[0]++;
+	}
+
+	ret = 0;
+
+out:
+	btrfs_release_path(&path);
+	return ret;
+}
+
 int BOX_MAIN(mkfs)(int argc, char **argv)
 {
 	char *file;
@@ -2312,6 +2412,15 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 		}
 	}
 
+	if (opt_discard) {
+		ret = discard_free_space(fs_info, metadata_profile);
+		if (ret < 0) {
+			errno = -ret;
+			error("failed to discard free space: %m");
+			goto out;
+		}
+	}
+
 	/*
 	 * The filesystem is now fully set up, commit the remaining changes and
 	 * fix the signature as the last step before closing the devices.