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-rw-r--r--gpxe/src/net/tcp.c67
1 files changed, 50 insertions, 17 deletions
diff --git a/gpxe/src/net/tcp.c b/gpxe/src/net/tcp.c
index da8e87b4..df87fc14 100644
--- a/gpxe/src/net/tcp.c
+++ b/gpxe/src/net/tcp.c
@@ -65,6 +65,11 @@ struct tcp_connection {
* Equivalent to RCV.NXT in RFC 793 terminology.
*/
uint32_t rcv_ack;
+ /** Receive window
+ *
+ * Equivalent to RCV.WND in RFC 793 terminology.
+ */
+ uint32_t rcv_win;
/** Most recent received timestamp
*
* Equivalent to TS.Recent in RFC 1323 terminology.
@@ -394,7 +399,7 @@ static int tcp_xmit ( struct tcp_connection *tcp, int force_send ) {
size_t len = 0;
size_t seq_len;
size_t app_win;
- size_t rcv_win;
+ size_t max_rcv_win;
/* If retransmission timer is already running, do nothing */
if ( timer_running ( &tcp->timer ) )
@@ -439,14 +444,16 @@ static int tcp_xmit ( struct tcp_connection *tcp, int force_send ) {
/* Fill data payload from transmit queue */
tcp_process_queue ( tcp, len, iobuf, 0 );
- /* Estimate window size */
- rcv_win = ( ( freemem * 3 ) / 4 );
- if ( rcv_win > TCP_MAX_WINDOW_SIZE )
- rcv_win = TCP_MAX_WINDOW_SIZE;
+ /* Expand receive window if possible */
+ max_rcv_win = ( ( freemem * 3 ) / 4 );
+ if ( max_rcv_win > TCP_MAX_WINDOW_SIZE )
+ max_rcv_win = TCP_MAX_WINDOW_SIZE;
app_win = xfer_window ( &tcp->xfer );
- if ( rcv_win > app_win )
- rcv_win = app_win;
- rcv_win &= ~0x03; /* Keep everything dword-aligned */
+ if ( max_rcv_win > app_win )
+ max_rcv_win = app_win;
+ max_rcv_win &= ~0x03; /* Keep everything dword-aligned */
+ if ( tcp->rcv_win < max_rcv_win )
+ tcp->rcv_win = max_rcv_win;
/* Fill up the TCP header */
payload = iobuf->data;
@@ -472,7 +479,7 @@ static int tcp_xmit ( struct tcp_connection *tcp, int force_send ) {
tcphdr->ack = htonl ( tcp->rcv_ack );
tcphdr->hlen = ( ( payload - iobuf->data ) << 2 );
tcphdr->flags = flags;
- tcphdr->win = htons ( rcv_win );
+ tcphdr->win = htons ( tcp->rcv_win );
tcphdr->csum = tcpip_chksum ( iobuf->data, iob_len ( iobuf ) );
/* Dump header */
@@ -633,6 +640,21 @@ static void tcp_rx_opts ( struct tcp_connection *tcp, const void *data,
}
/**
+ * Consume received sequence space
+ *
+ * @v tcp TCP connection
+ * @v seq_len Sequence space length to consume
+ */
+static void tcp_rx_seq ( struct tcp_connection *tcp, size_t seq_len ) {
+ tcp->rcv_ack += seq_len;
+ if ( tcp->rcv_win > seq_len ) {
+ tcp->rcv_win -= seq_len;
+ } else {
+ tcp->rcv_win = 0;
+ }
+}
+
+/**
* Handle TCP received SYN
*
* @v tcp TCP connection
@@ -659,7 +681,7 @@ static int tcp_rx_syn ( struct tcp_connection *tcp, uint32_t seq,
TCP_STATE_RCVD ( TCP_SYN ) );
/* Acknowledge SYN */
- tcp->rcv_ack++;
+ tcp_rx_seq ( tcp, 1 );
return 0;
}
@@ -747,7 +769,8 @@ static int tcp_rx_data ( struct tcp_connection *tcp, uint32_t seq,
return rc;
/* Acknowledge new data */
- tcp->rcv_ack += len;
+ tcp_rx_seq ( tcp, len );
+
return 0;
}
@@ -766,7 +789,7 @@ static int tcp_rx_fin ( struct tcp_connection *tcp, uint32_t seq ) {
/* Mark FIN as received and acknowledge it */
tcp->tcp_state |= TCP_STATE_RCVD ( TCP_FIN );
- tcp->rcv_ack++;
+ tcp_rx_seq ( tcp, 1 );
/* Close connection */
tcp_close ( tcp, 0 );
@@ -789,7 +812,7 @@ static int tcp_rx_rst ( struct tcp_connection *tcp, uint32_t seq ) {
* ACKed.
*/
if ( tcp->tcp_state & TCP_STATE_RCVD ( TCP_SYN ) ) {
- if ( ( tcp->rcv_ack - seq ) > 0 )
+ if ( ( seq - tcp->rcv_ack ) >= tcp->rcv_win )
return 0;
} else {
if ( ! ( tcp->tcp_state & TCP_STATE_ACKED ( TCP_SYN ) ) )
@@ -850,7 +873,8 @@ static int tcp_rx ( struct io_buffer *iobuf,
rc = -EINVAL;
goto discard;
}
- csum = tcpip_continue_chksum ( pshdr_csum, iobuf->data, iob_len ( iobuf ));
+ csum = tcpip_continue_chksum ( pshdr_csum, iobuf->data,
+ iob_len ( iobuf ) );
if ( csum != 0 ) {
DBG ( "TCP checksum incorrect (is %04x including checksum "
"field, should be 0000)\n", csum );
@@ -922,10 +946,19 @@ static int tcp_rx ( struct io_buffer *iobuf,
/* Dump out any state change as a result of the received packet */
tcp_dump_state ( tcp );
- /* Send out any pending data. If peer is expecting an ACK for
- * this packet then force sending a reply.
+ /* Send out any pending data. We force sending a reply if either
+ *
+ * a) the peer is expecting an ACK (i.e. consumed sequence space), or
+ * b) either end of the packet was outside the receive window
+ *
+ * Case (b) enables us to support TCP keepalives using
+ * zero-length packets, which we would otherwise ignore. Note
+ * that for case (b), we need *only* consider zero-length
+ * packets, since non-zero-length packets will already be
+ * caught by case (a).
*/
- tcp_xmit ( tcp, ( start_seq != seq ) );
+ tcp_xmit ( tcp, ( ( start_seq != seq ) ||
+ ( ( seq - tcp->rcv_ack ) > tcp->rcv_win ) ) );
/* If this packet was the last we expect to receive, set up
* timer to expire and cause the connection to be freed.