From a681e44ec60179567fb10f34351d7dfdbd2e7c7e Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 4 Feb 2026 21:41:36 +1000 Subject: tcp: Extend tcp_send_flag() to send TCP keepalive segments TCP keepalives aren't technically a flag, but they are a zero-data segment so they can be generated with only a small modification to tcp_{buf,vu}_send_flag(). Implement this, using a new "pseudo-flag" value (similar to DUP_ACK), KEEPALIVE. Signed-off-by: David Gibson [sbrivio: Fix trivial merge conflict with 812cdb802c6e] Signed-off-by: Stefano Brivio --- tcp_buf.c | 4 ++++ tcp_internal.h | 2 ++ tcp_vu.c | 3 +++ 3 files changed, 9 insertions(+) diff --git a/tcp_buf.c b/tcp_buf.c index 675ec13..41965b1 100644 --- a/tcp_buf.c +++ b/tcp_buf.c @@ -229,6 +229,10 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) tcp_frame_conns[tcp_payload_used++] = conn; l4len = optlen + sizeof(struct tcphdr); iov[TCP_IOV_PAYLOAD].iov_len = l4len; + + if (flags & KEEPALIVE) + seq--; + tcp_l2_buf_fill_headers(c, conn, iov, NULL, seq, false); tcp_l2_buf_pad(iov); diff --git a/tcp_internal.h b/tcp_internal.h index 518913b..1d335be 100644 --- a/tcp_internal.h +++ b/tcp_internal.h @@ -38,6 +38,8 @@ /* Flags for internal usage */ #define DUP_ACK (1 << 5) +#define KEEPALIVE (1 << 6) + #define OPT_EOL 0 #define OPT_NOP 1 #define OPT_MSS 2 diff --git a/tcp_vu.c b/tcp_vu.c index 171fb29..bb05fbf 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -134,6 +134,9 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) flags_elem[0].in_sg[0].iov_len = hdrlen + optlen; payload = IOV_TAIL(flags_elem[0].in_sg, 1, hdrlen); + if (flags & KEEPALIVE) + seq--; + tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload, NULL, seq, !*c->pcap); -- cgit v1.2.3