Re: [PATCH v1 2/2] tap, tcp, udp: Use rate-limited logging

On Wed, 1 Apr 2026 23:59:10 +0530 Anshu Kumari wrote:

Now that rate-limited logging macros are available, promote several debug messages to higher severity levels. These messages were previously kept at debug to prevent guests from flooding host logs, but with rate limiting they can safely be made visible in normal operation.

In tap.c, refactor tap4_is_fragment() to use warn_ratelimit() instead of its ad-hoc rate limiting, and promote the guest MAC address change message to info level.

In tcp.c, promote the invalid TCP SYN endpoint message to warn level.

In udp.c and udp_flow.c, promote flow allocation failures and dropped datagram messages to warn level, and rate-limit the unrecoverable socket error message.

Link: https://bugs.passt.top/show_bug.cgi?id=134

By the way of this ticket, I forgot to mention that as it came up after a discussion on a series by Volker (Volker Diels-Grabsch ), it would be nice to Cc: him on the next version of this patch.

Signed-off-by: Anshu Kumari ---

- Inside udp.c - David: should this be changed to warn_ratelimit? I am not sure about it debug("%s error on UDP socket %i: %s", str_ee_origin(ee), s, strerror_(ee->ee_errno));

I had a closer look, and it looks like we're hitting that part for any error reported via ICMP that can be associated to a given UDP socket, so I would say it's part of our regular networking operation, and we should keep it as debug().

--- tap.c | 14 ++++---------- tcp.c | 2 +- udp.c | 6 +++--- udp_flow.c | 4 ++-- 4 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/tap.c b/tap.c index 1049e02..f569b61 100644 --- a/tap.c +++ b/tap.c @@ -686,17 +686,11 @@ static bool tap4_is_fragment(const struct iphdr *iph, const struct timespec *now) { if (ntohs(iph->frag_off) & ~IP_DF) { - /* Ratelimit messages */ - static time_t last_message; static unsigned num_dropped;

num_dropped++; - if (now->tv_sec - last_message > FRAGMENT_MSG_RATE) { - warn("Can't process IPv4 fragments (%u dropped)", - num_dropped); - last_message = now->tv_sec; - num_dropped = 0; - } + warn_ratelimit(now, "Can't process IPv4 fragments (%u dropped)", + num_dropped); return true; } return false; @@ -1115,8 +1109,8 @@ void tap_add_packet(struct ctx *c, struct iov_tail *data, char bufmac[ETH_ADDRSTRLEN];

memcpy(c->guest_mac, eh->h_source, ETH_ALEN); - debug("New guest MAC address observed: %s", - eth_ntop(c->guest_mac, bufmac, sizeof(bufmac))); + info_ratelimit(now, "New guest MAC address observed: %s", + eth_ntop(c->guest_mac, bufmac, sizeof(bufmac)));

Similar to the other call Laurent commented on, this should be: info_ratelimit(now, "New guest MAC address observed: %s", eth_ntop(c->guest_mac, bufmac, sizeof(bufmac))); so that arguments visually align with each other. This is the style (somewhat) suggested at: https://docs.kernel.org/process/coding-style.html#breaking-long-lines-and-st... which is the one we follow.

proto_update_l2_buf(c->guest_mac); }

diff --git a/tcp.c b/tcp.c index 8ea9be8..3d3b80d 100644 --- a/tcp.c +++ b/tcp.c @@ -1688,7 +1688,7 @@ static void tcp_conn_from_tap(const struct ctx *c, sa_family_t af, !inany_is_unicast(&ini->oaddr) || ini->oport == 0) { char sstr[INANY_ADDRSTRLEN], dstr[INANY_ADDRSTRLEN];

- debug("Invalid endpoint in TCP SYN: %s:%hu -> %s:%hu", + warn_ratelimit(now, "Invalid endpoint in TCP SYN: %s:%hu -> %s:%hu", inany_ntop(&ini->eaddr, sstr, sizeof(sstr)), ini->eport, inany_ntop(&ini->oaddr, dstr, sizeof(dstr)), ini->oport); goto cancel; diff --git a/udp.c b/udp.c index 1fc5a42..1ef5e7a 100644 --- a/udp.c +++ b/udp.c @@ -871,7 +871,7 @@ void udp_sock_fwd(const struct ctx *c, int s, int rule_hint, /* Clear errors & carry on */ if (udp_sock_errs(c, s, FLOW_SIDX_NONE, frompif, port) < 0) { - err( + err_ratelimit(now, "UDP: Unrecoverable error on listening socket: (%s port %hu)", pif_name(frompif), port); /* FIXME: what now? close/re-open socket? */ @@ -898,7 +898,7 @@ void udp_sock_fwd(const struct ctx *c, int s, int rule_hint, pif_name(frompif), pif_name(topif)); discard = true; } else { - debug("Discarding datagram without flow"); + warn_ratelimit(now, "Discarding datagram without flow"); discard = true; }

@@ -1042,7 +1042,7 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif, if (!(uflow = udp_at_sidx(tosidx))) { char sstr[INET6_ADDRSTRLEN], dstr[INET6_ADDRSTRLEN];

- debug("Dropping datagram with no flow %s %s:%hu -> %s:%hu", + warn_ratelimit(now, "Dropping datagram with no flow %s %s:%hu -> %s:%hu", pif_name(pif), inet_ntop(af, saddr, sstr, sizeof(sstr)), src, inet_ntop(af, daddr, dstr, sizeof(dstr)), dst); diff --git a/udp_flow.c b/udp_flow.c index 7e2453e..9343b4b 100644 --- a/udp_flow.c +++ b/udp_flow.c @@ -235,7 +235,7 @@ flow_sidx_t udp_flow_from_sock(const struct ctx *c, uint8_t pif, if (!(flow = flow_alloc())) { char sastr[SOCKADDR_STRLEN];

- debug("Couldn't allocate flow for UDP datagram from %s %s", + warn_ratelimit(now, "Couldn't allocate flow for UDP datagram from %s %s", pif_name(pif), sockaddr_ntop(s_in, sastr, sizeof(sastr))); return FLOW_SIDX_NONE; } @@ -292,7 +292,7 @@ flow_sidx_t udp_flow_from_tap(const struct ctx *c, if (!(flow = flow_alloc())) { char sstr[INET6_ADDRSTRLEN], dstr[INET6_ADDRSTRLEN];

- debug("Couldn't allocate flow for UDP datagram from %s %s:%hu -> %s:%hu", + warn_ratelimit(now, "Couldn't allocate flow for UDP datagram from %s %s:%hu -> %s:%hu", pif_name(pif), inet_ntop(af, saddr, sstr, sizeof(sstr)), srcport, inet_ntop(af, daddr, dstr, sizeof(dstr)), dstport);

Other than that, and other than the pending comments from Laurent, the patch looks good to me! I would suggest maybe waiting about one more day before posting the next version to give others better chances to review. -- Stefano