main/streams/streams: use copy_file_range() on Linux

copy_file_range() is a Linux-specific system call which allows
efficient copying between two file descriptors, eliminating the need
to transfer data from the kernel to userspace and back.  For
networking file systems like NFS and Ceph, it even eliminates copying
data to the client, and local filesystems like Btrfs and XFS can
create shared extents.

Author: MaxKellermann

main/streams/streams.c

@@ -1555,6 +1555,81 @@ PHPAPI zend_result _php_stream_copy_to_stream_ex(php_stream *src, php_stream *de
 		return SUCCESS;
 	}
 
+#ifdef __linux__
+	if (php_stream_is(src, PHP_STREAM_IS_STDIO) &&
+	    php_stream_is(dest, PHP_STREAM_IS_STDIO) &&
+	    src->writepos == src->readpos &&
+	    php_stream_can_cast(src, PHP_STREAM_AS_FD) == SUCCESS &&
+	    php_stream_can_cast(dest, PHP_STREAM_AS_FD) == SUCCESS) {
+		/* both php_stream instances are backed by a file
+		   descriptor, are not filtered and the read buffer is
+		   empty: we can use copy_file_range() */
+
+		int src_fd, dest_fd;
+
+		php_stream_cast(src, PHP_STREAM_AS_FD, (void*)&src_fd, 0);
+		php_stream_cast(dest, PHP_STREAM_AS_FD, (void*)&dest_fd, 0);
+
+		/* copy_file_range() is a Linux-specific system call
+		   which allows efficient copying between two file
+		   descriptors, eliminating the need to transfer data
+		   from the kernel to userspace and back.  For
+		   networking file systems like NFS and Ceph, it even
+		   eliminates copying data to the client, and local
+		   filesystems like Btrfs and XFS can create shared
+		   extents. */
+
+		ssize_t cfr = copy_file_range(src_fd, NULL,
+					      dest_fd, NULL,
+					      maxlen, 0);
+		if (cfr > 0) {
+			size_t nbytes = (size_t)cfr;
+			haveread += nbytes;
+
+			src->position += nbytes;
+			dest->position += nbytes;
+
+			if ((maxlen != PHP_STREAM_COPY_ALL && nbytes == maxlen) ||
+			    php_stream_eof(src)) {
+				/* the whole request was satisfied or
+				   end-of-file reached - done */
+				*len = haveread;
+				return SUCCESS;
+			}
+
+			/* there may be more data; continue copying
+			   using the fallback code below */
+		} else if (cfr == 0) {
+			/* end of file */
+			*len = haveread;
+			return SUCCESS;
+		} else if (cfr < 0) {
+			switch (errno) {
+			case EINVAL:
+				/* some formal error, e.g. overlapping
+				   file ranges */
+				break;
+
+			case EXDEV:
+				/* pre Linux 5.3 error */
+				break;
+
+			case ENOSYS:
+				/* not implemented by this Linux kernel */
+				break;
+
+			default:
+				/* unexpected I/O error - give up, no
+				   fallback */
+				*len = haveread;
+				return FAILURE;
+			}
+
+			/* fall back to classic copying */
+		}
+	}
+#endif
+
 	if (maxlen == PHP_STREAM_COPY_ALL) {
 		maxlen = 0;
 	}