[PATCH v2] tap, tcp, udp: Use rate-limited logging

[PATCH v2] tap, tcp, udp: Use rate-limited logging

[Anshu Kumari]

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
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v2:
  - removed #define FRAGMENT_MSG_RATE
  - fixed the indentation for "Invalid endpoint in TCP SYN" log.


- 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));

---
 tap.c      | 15 ++++-----------
 tcp.c      |  6 +++---
 udp.c      |  6 +++---
 udp_flow.c |  4 ++--
 4 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/tap.c b/tap.c
index 1049e02..b7270d9 100644
--- a/tap.c
+++ b/tap.c
@@ -99,7 +99,6 @@ static PACKET_POOL_NOINIT(pool_tap4, TAP_MSGS_IP4);
 static PACKET_POOL_NOINIT(pool_tap6, TAP_MSGS_IP6);
 
 #define TAP_SEQS		128 /* Different L4 tuples in one batch */
-#define FRAGMENT_MSG_RATE	10  /* # seconds between fragment warnings */
 
 /**
  * tap_l2_max_len() - Maximum frame size (including L2 header) for current mode
@@ -686,17 +685,11 @@ 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 +1108,8 @@ 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)));
 		proto_update_l2_buf(c->guest_mac);
 	}
 
diff --git a/tcp.c b/tcp.c
index 8ea9be8..964cfc2 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1688,9 +1688,9 @@ 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",
-		      inany_ntop(&ini->eaddr, sstr, sizeof(sstr)), ini->eport,
-		      inany_ntop(&ini->oaddr, dstr, sizeof(dstr)), ini->oport);
+		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);
-- 
2.53.0

Re: [PATCH v2] tap, tcp, udp: Use rate-limited logging

[Stefano Brivio]

On Mon,  6 Apr 2026 13:35:56 +0530
Anshu Kumari <anskuma@redhat.com> 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
> Signed-off-by: Anshu Kumari <anskuma@redhat.com>
> ---
> v2:
>   - removed #define FRAGMENT_MSG_RATE
>   - fixed the indentation for "Invalid endpoint in TCP SYN" log.

Sorry, I replied to v1 a couple minutes before getting your v2. Note
that you didn't really address some of the pending comments (about
indentation), see my reply for more details.

I would suggest anyway to wait one day or so before posting a new
version, thanks.

-- 
Stefano

Re: [PATCH v2] tap, tcp, udp: Use rate-limited logging

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 6599 bytes --]

On Mon, Apr 06, 2026 at 01:35:56PM +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
> Signed-off-by: Anshu Kumari <anskuma@redhat.com>

Stefano noted the minor indenting nit, and I have a couple of
suggestions for error level.  Otherwise LGTM.

> ---
> v2:
>   - removed #define FRAGMENT_MSG_RATE
>   - fixed the indentation for "Invalid endpoint in TCP SYN" log.
> 
> 
> - 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));
> 
> ---
>  tap.c      | 15 ++++-----------
>  tcp.c      |  6 +++---
>  udp.c      |  6 +++---
>  udp_flow.c |  4 ++--
>  4 files changed, 12 insertions(+), 19 deletions(-)
> 
> diff --git a/tap.c b/tap.c
> index 1049e02..b7270d9 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -99,7 +99,6 @@ static PACKET_POOL_NOINIT(pool_tap4, TAP_MSGS_IP4);
>  static PACKET_POOL_NOINIT(pool_tap6, TAP_MSGS_IP6);
>  
>  #define TAP_SEQS		128 /* Different L4 tuples in one batch */
> -#define FRAGMENT_MSG_RATE	10  /* # seconds between fragment warnings */
>  
>  /**
>   * tap_l2_max_len() - Maximum frame size (including L2 header) for current mode
> @@ -686,17 +685,11 @@ 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 +1108,8 @@ 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)));
>  		proto_update_l2_buf(c->guest_mac);
>  	}
>  
> diff --git a/tcp.c b/tcp.c
> index 8ea9be8..964cfc2 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -1688,9 +1688,9 @@ 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",
> -		      inany_ntop(&ini->eaddr, sstr, sizeof(sstr)), ini->eport,
> -		      inany_ntop(&ini->oaddr, dstr, sizeof(dstr)), ini->oport);
> +		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)));

I think this one should go up to err() status.  The previous ones
could be caused by bogus packets from guest or peer.  This one
definitely indicates we're not able to forward legitimate looking traffic.

>  		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",

Same for this one.

>  		      pif_name(pif),
>  		      inet_ntop(af, saddr, sstr, sizeof(sstr)), srcport,
>  		      inet_ntop(af, daddr, dstr, sizeof(dstr)), dstport);
> -- 
> 2.53.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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