Separate the "is data ready" function of xfer_seek() into an

xfer_window() function, which can return a scalar rather than a
boolean.

src/net/tcp.c

@@ -897,31 +897,28 @@ static void tcp_xfer_close ( struct xfer_interface *xfer, int rc ) {
 }
 
 /**
- * Seek to position
+ * Check flow control window
  *
  * @v xfer		Data transfer interface
- * @v offset		Offset to new position
- * @v whence		Basis for new position
- * @ret rc		Return status code
+ * @ret len		Length of window
  */
-static int tcp_xfer_seek ( struct xfer_interface *xfer, off_t offset,
-			   int whence ) {
+static size_t tcp_xfer_window ( struct xfer_interface *xfer ) {
 	struct tcp_connection *tcp =
 		container_of ( xfer, struct tcp_connection, xfer );
 
-	/* TCP doesn't support seeking to arbitrary positions */
-	if ( ( whence != SEEK_CUR ) || ( offset != 0 ) )
-		return -EINVAL;
-
 	/* Not ready if we're not in a suitable connection state */
 	if ( ! TCP_CAN_SEND_DATA ( tcp->tcp_state ) )
-		return -EAGAIN;
+		return 0;
 
-	/* Not ready if data queue is non-empty */
+	/* Not ready if data queue is non-empty.  This imposes a limit
+	 * of only one unACKed packet in the TX queue at any time; we
+	 * do this to conserve memory usage.
+	 */
 	if ( ! list_empty ( &tcp->queue ) )
-		return -EAGAIN;
+		return 0;
 
-	return 0;
+	/* Return TCP window length */
+	return tcp->snd_win;
 }
 
 /**
@@ -951,7 +948,8 @@ static int tcp_xfer_deliver_iob ( struct xfer_interface *xfer,
 static struct xfer_interface_operations tcp_xfer_operations = {
 	.close		= tcp_xfer_close,
 	.vredirect	= ignore_xfer_vredirect,
-	.seek		= tcp_xfer_seek,
+	.seek		= ignore_xfer_seek,
+	.window		= tcp_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= tcp_xfer_deliver_iob,
 	.deliver_raw	= xfer_deliver_as_iob,

src/net/tcp/ftp.c

@@ -297,6 +297,7 @@ static struct xfer_interface_operations ftp_control_operations = {
 	.close		= ftp_control_close,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= ftp_control_deliver_raw,
@@ -361,6 +362,7 @@ static struct xfer_interface_operations ftp_data_operations = {
 	.close		= ftp_data_closed,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= ftp_data_deliver_iob,
 	.deliver_raw	= xfer_deliver_as_iob,
@@ -393,6 +395,7 @@ static struct xfer_interface_operations ftp_xfer_operations = {
 	.close		= ftp_xfer_closed,
 	.vredirect	= ignore_xfer_vredirect,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= ignore_xfer_deliver_raw,

src/net/tcp/http.c

@@ -388,7 +388,7 @@ static void http_step ( struct process *process ) {
 	const char *query = http->uri->query;
 	int rc;
 
-	if ( xfer_ready ( &http->socket ) == 0 ) {
+	if ( xfer_window ( &http->socket ) ) {
 		process_del ( &http->process );
 		if ( ( rc = xfer_printf ( &http->socket,
 					  "GET %s%s%s HTTP/1.1\r\n"
@@ -425,6 +425,7 @@ static struct xfer_interface_operations http_socket_operations = {
 	.close		= http_socket_close,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= http_socket_deliver_iob,
 	.deliver_raw	= xfer_deliver_as_iob,
@@ -451,6 +452,7 @@ static struct xfer_interface_operations http_xfer_operations = {
 	.close		= http_xfer_close,
 	.vredirect	= ignore_xfer_vredirect,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= ignore_xfer_deliver_raw,

src/net/udp.c

@@ -415,6 +415,7 @@ static struct xfer_interface_operations udp_xfer_operations = {
 	.close		= udp_xfer_close,
 	.vredirect	= ignore_xfer_vredirect,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= udp_alloc_iob,
 	.deliver_iob	= udp_xfer_deliver_iob,
 	.deliver_raw	= xfer_deliver_as_iob,

src/net/udp/dhcp.c

@@ -722,6 +722,7 @@ static struct xfer_interface_operations dhcp_xfer_operations = {
 	.close		= ignore_xfer_close,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= dhcp_deliver_raw,
 };

src/net/udp/dns.c

@@ -433,6 +433,7 @@ static struct xfer_interface_operations dns_socket_operations = {
 	.close		= dns_xfer_close,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= dns_xfer_deliver_raw,

src/net/udp/tftp.c

@@ -583,6 +583,7 @@ static struct xfer_interface_operations tftp_socket_operations = {
 	.close		= tftp_socket_close,
 	.vredirect	= xfer_vopen,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= tftp_socket_deliver_iob,
 	.deliver_raw	= xfer_deliver_as_iob,
@@ -609,6 +610,7 @@ static struct xfer_interface_operations tftp_xfer_operations = {
 	.close		= tftp_xfer_close,
 	.vredirect	= ignore_xfer_vredirect,
 	.seek		= ignore_xfer_seek,
+	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
 	.deliver_iob	= xfer_deliver_as_raw,
 	.deliver_raw	= ignore_xfer_deliver_raw,