diff options
| -rw-r--r-- | tcp.c | 65 | ||||
| -rw-r--r-- | tcp_conn.h | 7 |
2 files changed, 12 insertions, 60 deletions
@@ -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) @@ -85,10 +85,9 @@ struct tcp_tap_conn { uint8_t flags; #define STALLED BIT(0) #define LOCAL BIT(1) -#define WND_CLAMPED BIT(2) -#define ACTIVE_CLOSE BIT(3) -#define ACK_TO_TAP_DUE BIT(4) -#define ACK_FROM_TAP_DUE BIT(5) +#define ACTIVE_CLOSE BIT(2) +#define ACK_TO_TAP_DUE BIT(3) +#define ACK_FROM_TAP_DUE BIT(4) #define TCP_MSS_BITS 14 |