@@ -65,6 +65,19 @@ dump the stream metadata, one line per operation
 +
 Does not require the 'path' parameter. The filesystem remains unchanged.
 
+--clone-fallback::
+allow failed clone operation to fallback to buffer copy from source file.
++
+Clone operations have various requirement which can be affected by things like
+mount options (source file has no NODATASUM flag while current fs is mounted
+with NODATASUM), sectorsizes (the stream is from 4K sectorsize fs while the fs
+is in 64K page size).
++
+This option allows users to let receive to handle such failed clone with
+buffered copy from the source, at the cost of less clone operations and even
+some unexposed send bugs. Thus this behavior must be explicitly specified by
+the user.
+
 -q|--quiet::
 (deprecated) alias for global '-q' option
 

@@ -76,6 +76,8 @@ struct btrfs_receive
 	struct subvol_uuid_search sus;
 
 	int honor_end_cmd;
+
+	bool clone_fallback;
 };
 
 static int finish_subvol(struct btrfs_receive *rctx)

@@ -705,6 +707,44 @@ out:
 	return ret;
 }
 
+static int buffered_copy(int src_fd, int dst_fd, u64 src_offset, u64 len,
+			 u64 dest_offset)
+{
+	unsigned char buf[SZ_32K];
+	u64 copied = 0;
+	int ret = 0;
+
+	while (copied < len) {
+		u32 copy_len = min_t(u32, ARRAY_SIZE(buf), len - copied);
+		u32 written = 0;
+		ssize_t read_size;
+
+		read_size = pread(src_fd, buf, copy_len, src_offset + copied);
+		if (read < 0) {
+			ret = -errno;
+			error("failed to read source file: %m");
+			return ret;
+		}
+
+		/* Write the buffer to dest file */
+		while (written < read_size) {
+			ssize_t write_size;
+
+			write_size = pwrite(dst_fd, buf + written,
+					read_size - written,
+					dest_offset + copied + written);
+			if (write_size < 0) {
+				ret = -errno;
+				error("failed to write source file: %m");
+				return ret;
+			}
+			written += write_size;
+		}
+		copied += read_size;
+	}
+	return ret;
+}
+
 static int process_clone(const char *path, u64 offset, u64 len,
 			 const u8 *clone_uuid, u64 clone_ctransid,
 			 const char *clone_path, u64 clone_offset,

@@ -788,8 +828,17 @@ static int process_clone(const char *path, u64 offset, u64 len,
 	ret = ioctl(rctx->write_fd, BTRFS_IOC_CLONE_RANGE, &clone_args);
 	if (ret < 0) {
 		ret = -errno;
-		error("failed to clone extents to %s: %m", path);
-		goto out;
+		if (ret != -EINVAL || !rctx->clone_fallback) {
+			error("failed to clone extents to %s: %m", path);
+			goto out;
+		}
+
+		if (bconf.verbose >= 2)
+			warning(
+		"failed to clone extents to %s, fallback to buffered write",
+				path);
+		ret = buffered_copy(clone_fd, rctx->write_fd, clone_offset,
+				    len, offset);
 	}
 
 out:

@@ -1238,11 +1287,13 @@ static int cmd_receive(const struct cmd_struct *cmd, int argc, char **argv)
 	optind = 0;
 	while (1) {
 		int c;
-		enum { GETOPT_VAL_DUMP = 257 };
+		enum { GETOPT_VAL_DUMP = 257, GETOPT_VAL_CLONE_FALLBACK };
 		static const struct option long_opts[] = {
 			{ "max-errors", required_argument, NULL, 'E' },
 			{ "chroot", no_argument, NULL, 'C' },
 			{ "dump", no_argument, NULL, GETOPT_VAL_DUMP },
+			{ "clone-fallback", no_argument, NULL,
+				GETOPT_VAL_CLONE_FALLBACK},
 			{ "quiet", no_argument, NULL, 'q' },
 			{ NULL, 0, NULL, 0 }
 		};

@@ -1286,6 +1337,9 @@ static int cmd_receive(const struct cmd_struct *cmd, int argc, char **argv)
 		case GETOPT_VAL_DUMP:
 			dump = 1;
 			break;
+		case GETOPT_VAL_CLONE_FALLBACK:
+			rctx.clone_fallback = true;
+			break;
 		default:
 			usage_unknown_option(cmd, argv);
 		}