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Diffstat (limited to 'tcp.c')
-rw-r--r--tcp.c65
1 files changed, 9 insertions, 56 deletions
diff --git a/tcp.c b/tcp.c
index 13e82ca..cfcd40a 100644
--- a/tcp.c
+++ b/tcp.c
@@ -46,8 +46,8 @@
* - avoiding port and address translations whenever possible
* - mirroring TCP dynamics by observation of socket parameters (TCP_INFO
* socket option) and TCP headers of packets coming from the tap interface,
- * reapplying those parameters in both flow directions (including TCP_MSS,
- * TCP_WINDOW_CLAMP socket options)
+ * reapplying those parameters in both flow directions (including TCP_MSS
+ * socket option)
* - simplicity: only a small subset of TCP logic is implemented here and
* delegated as much as possible to the TCP implementations of guest and host
* kernel. This is achieved by:
@@ -236,12 +236,10 @@
* - update @seq_ack_from_tap from ack_seq in header
* - on two duplicated ACKs, reset @seq_to_tap to @seq_ack_from_tap, and
* resend with steps listed above
- * - set TCP_WINDOW_CLAMP from TCP header from tap
*
* - from tap/guest to socket:
* - on packet from tap/guest:
* - set @ts_tap_act
- * - set TCP_WINDOW_CLAMP from TCP header from tap
* - check seq from header against @seq_from_tap, if data is missing, send
* two ACKs with number @seq_ack_to_tap, discard packet
* - otherwise queue data to socket, set @seq_from_tap to seq from header
@@ -420,7 +418,7 @@ static const char *tcp_state_str[] __attribute((__unused__)) = {
};
static const char *tcp_flag_str[] __attribute((__unused__)) = {
- "STALLED", "LOCAL", "WND_CLAMPED", "ACTIVE_CLOSE", "ACK_TO_TAP_DUE",
+ "STALLED", "LOCAL", "ACTIVE_CLOSE", "ACK_TO_TAP_DUE",
"ACK_FROM_TAP_DUE",
};
@@ -1790,58 +1788,16 @@ static void tcp_get_tap_ws(struct tcp_tap_conn *conn,
/**
* tcp_tap_window_update() - Process an updated window from tap side
- * @c: Execution context
* @conn: Connection pointer
* @window: Window value, host order, unscaled
*/
-static void tcp_tap_window_update(const struct ctx *c,
- struct tcp_tap_conn *conn, unsigned wnd)
+static void tcp_tap_window_update(struct tcp_tap_conn *conn, unsigned wnd)
{
- uint32_t prev_scaled = conn->wnd_from_tap << conn->ws_from_tap;
- int s = conn->sock;
-
wnd = MIN(MAX_WINDOW, wnd << conn->ws_from_tap);
conn->wnd_from_tap = MIN(wnd >> conn->ws_from_tap, USHRT_MAX);
- /* TODO: With (at least) Linux kernel versions 6.1 to 6.5, if we end up
- * with a zero-sized window on a TCP socket, dropping data (once
- * acknowledged by the guest) with recv() and MSG_TRUNC doesn't appear
- * to be enough to make the kernel advertise a non-zero window to the
- * sender. Forcing a TCP_WINDOW_CLAMP setting, even with the existing
- * value, fixes this.
- *
- * The STALLED flag on a connection is a sufficient indication that we
- * might have a zero-sized window on the socket, because it's set if we
- * exhausted the tap-side window, or if everything we receive from a
- * socket is already in flight to the guest.
- *
- * So, if STALLED is set, and we received a window value from the tap,
- * force a TCP_WINDOW_CLAMP setsockopt(). This should be investigated
- * further and fixed in the kernel instead, if confirmed.
- */
- if (!(conn->flags & STALLED) && conn->flags & WND_CLAMPED) {
- if (prev_scaled == wnd)
- return;
-
- /* Discard +/- 1% updates to spare some syscalls. */
- /* TODO: cppcheck, starting from commit b4d455df487c ("Fix
- * 11349: FP negativeIndex for clamped array index (#4627)"),
- * reports wnd > prev_scaled as always being true, see also:
- *
- * https://github.com/danmar/cppcheck/pull/4627
- *
- * drop this suppression once that's resolved.
- */
- /* cppcheck-suppress [knownConditionTrueFalse, unmatchedSuppression] */
- if ((wnd > prev_scaled && wnd * 99 / 100 < prev_scaled) ||
- (wnd < prev_scaled && wnd * 101 / 100 > prev_scaled))
- return;
- }
-
- if (setsockopt(s, SOL_TCP, TCP_WINDOW_CLAMP, &wnd, sizeof(wnd)))
- trace("TCP: failed to set TCP_WINDOW_CLAMP on socket %i", s);
-
- conn_flag(c, conn, WND_CLAMPED);
+ /* FIXME: reflect the tap-side receiver's window back to the sock-side
+ * sender by adjusting SO_RCVBUF? */
}
/**
@@ -2452,7 +2408,7 @@ static int tcp_data_from_tap(struct ctx *c, struct tcp_tap_conn *conn,
if (ack && !tcp_sock_consume(conn, max_ack_seq))
tcp_update_seqack_from_tap(c, conn, max_ack_seq);
- tcp_tap_window_update(c, conn, max_ack_seq_wnd);
+ tcp_tap_window_update(conn, max_ack_seq_wnd);
if (retr) {
trace("TCP: fast re-transmit, ACK: %u, previous sequence: %u",
@@ -2537,7 +2493,7 @@ static void tcp_conn_from_sock_finish(struct ctx *c, struct tcp_tap_conn *conn,
const struct tcphdr *th,
const char *opts, size_t optlen)
{
- tcp_tap_window_update(c, conn, ntohs(th->window));
+ tcp_tap_window_update(conn, ntohs(th->window));
tcp_get_tap_ws(conn, opts, optlen);
/* First value is not scaled */
@@ -2645,7 +2601,7 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, int af,
if (!th->ack)
goto reset;
- tcp_tap_window_update(c, conn, ntohs(th->window));
+ tcp_tap_window_update(conn, ntohs(th->window));
tcp_data_from_sock(c, conn);
@@ -2669,9 +2625,6 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, int af,
if (count == -1)
goto reset;
- /* Note: STALLED matters for tcp_tap_window_update(): unset it only
- * after processing data (and window) from the tap side
- */
conn_flag(c, conn, ~STALLED);
if (conn->seq_ack_to_tap != conn->seq_from_tap)