From 9e5df350d63b0819f04b44bb57ea146274a6b42f Mon Sep 17 00:00:00 2001 From: David Gibson Date: Mon, 21 Oct 2024 18:40:29 +1100 Subject: tcp: Use structures to construct initial TCP options As a rule, we prefer constructing packets with matching C structures, rather than building them byte by byte. However, one case we still build byte by byte is the TCP options we include in SYN packets (in fact the only time we generate TCP options on the tap interface). Rework this to use a structure and initialisers which make it a bit clearer what's going on. Signed-off-by: David Gibson Signed-off-by; Stefano Brivio --- tcp.c | 17 +++-------------- 1 file changed, 3 insertions(+), 14 deletions(-) (limited to 'tcp.c') diff --git a/tcp.c b/tcp.c index b2155ab..0d22e07 100644 --- a/tcp.c +++ b/tcp.c @@ -1232,7 +1232,7 @@ static void tcp_update_seqack_from_tap(const struct ctx *c, * 1 otherwise */ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn, - int flags, struct tcphdr *th, char *data, + int flags, struct tcphdr *th, struct tcp_syn_opts *opts, size_t *optlen) { struct tcp_info tinfo = { 0 }; @@ -1258,12 +1258,6 @@ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn, if (flags & SYN) { int mss; - /* Options: MSS, NOP and window scale (8 bytes) */ - *optlen = OPT_MSS_LEN + 1 + OPT_WS_LEN; - - *data++ = OPT_MSS; - *data++ = OPT_MSS_LEN; - if (c->mtu == -1) { mss = tinfo.tcpi_snd_mss; } else { @@ -1279,16 +1273,11 @@ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn, else if (mss > PAGE_SIZE) mss = ROUND_DOWN(mss, PAGE_SIZE); } - *(uint16_t *)data = htons(MIN(USHRT_MAX, mss)); - - data += OPT_MSS_LEN - 2; conn->ws_to_tap = MIN(MAX_WS, tinfo.tcpi_snd_wscale); - *data++ = OPT_NOP; - *data++ = OPT_WS; - *data++ = OPT_WS_LEN; - *data++ = conn->ws_to_tap; + *opts = TCP_SYN_OPTS(mss, conn->ws_to_tap); + *optlen = sizeof(*opts); } else if (!(flags & RST)) { flags |= ACK; } -- cgit v1.2.3