[PATCH net-next] selftests: udpgso: Pull up network setup into shell script

[PATCH net-next] selftests: udpgso: Pull up network setup into shell script

[Jakub Sitnicki]

udpgso regression test configures routing and device MTU directly through
uAPI (Netlink, ioctl) to do its job. While there is nothing wrong with it,
it takes more effort than doing it from shell.

Looking forward, we would like to extend the udpgso regression tests to
cover the EIO corner case [1], once it gets addressed. That will require a
dummy device and device feature manipulation to set it up. Which means more
Netlink code.

So, in preparation, pull out network configuration into the shell script
part of the test, so it is easily extendable in the future.

Also, because it now easy to setup routing, add a second local IPv6
address. Because the second address is not managed by the kernel, we can
"replace" the corresponding local route with a reduced-MTU one. This
unblocks the disabled "ipv6 connected" test case. Add a similar setup for
IPv4 for symmetry.

[1] https://lore.kernel.org/netdev/87jzqsld6q.fsf@cloudflare.com/

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
 tools/testing/selftests/net/udpgso.c  | 134 ++------------------------
 tools/testing/selftests/net/udpgso.sh |  50 ++++++++--
 2 files changed, 48 insertions(+), 136 deletions(-)

diff --git a/tools/testing/selftests/net/udpgso.c b/tools/testing/selftests/net/udpgso.c
index 7badaf215de2..79fd3287ff60 100644
--- a/tools/testing/selftests/net/udpgso.c
+++ b/tools/testing/selftests/net/udpgso.c
@@ -56,7 +56,6 @@ static bool		cfg_do_msgmore;
 static bool		cfg_do_setsockopt;
 static int		cfg_specific_test_id = -1;
 
-static const char	cfg_ifname[] = "lo";
 static unsigned short	cfg_port = 9000;
 
 static char buf[ETH_MAX_MTU];
@@ -69,8 +68,13 @@ struct testcase {
 	int r_len_last;		/* recv(): size of last non-mss dgram, if any */
 };
 
-const struct in6_addr addr6 = IN6ADDR_LOOPBACK_INIT;
-const struct in_addr addr4 = { .s_addr = __constant_htonl(INADDR_LOOPBACK + 2) };
+const struct in6_addr addr6 = {
+	{ { 0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x01 } },
+};
+
+const struct in_addr addr4 = {
+	__constant_htonl(0xc0000201), /* 192.0.2.1 */
+};
 
 struct testcase testcases_v4[] = {
 	{
@@ -274,48 +278,6 @@ struct testcase testcases_v6[] = {
 	}
 };
 
-static unsigned int get_device_mtu(int fd, const char *ifname)
-{
-	struct ifreq ifr;
-
-	memset(&ifr, 0, sizeof(ifr));
-
-	strcpy(ifr.ifr_name, ifname);
-
-	if (ioctl(fd, SIOCGIFMTU, &ifr))
-		error(1, errno, "ioctl get mtu");
-
-	return ifr.ifr_mtu;
-}
-
-static void __set_device_mtu(int fd, const char *ifname, unsigned int mtu)
-{
-	struct ifreq ifr;
-
-	memset(&ifr, 0, sizeof(ifr));
-
-	ifr.ifr_mtu = mtu;
-	strcpy(ifr.ifr_name, ifname);
-
-	if (ioctl(fd, SIOCSIFMTU, &ifr))
-		error(1, errno, "ioctl set mtu");
-}
-
-static void set_device_mtu(int fd, int mtu)
-{
-	int val;
-
-	val = get_device_mtu(fd, cfg_ifname);
-	fprintf(stderr, "device mtu (orig): %u\n", val);
-
-	__set_device_mtu(fd, cfg_ifname, mtu);
-	val = get_device_mtu(fd, cfg_ifname);
-	if (val != mtu)
-		error(1, 0, "unable to set device mtu to %u\n", val);
-
-	fprintf(stderr, "device mtu (test): %u\n", val);
-}
-
 static void set_pmtu_discover(int fd, bool is_ipv4)
 {
 	int level, name, val;
@@ -354,81 +316,6 @@ static unsigned int get_path_mtu(int fd, bool is_ipv4)
 	return mtu;
 }
 
-/* very wordy version of system("ip route add dev lo mtu 1500 127.0.0.3/32") */
-static void set_route_mtu(int mtu, bool is_ipv4)
-{
-	struct sockaddr_nl nladdr = { .nl_family = AF_NETLINK };
-	struct nlmsghdr *nh;
-	struct rtattr *rta;
-	struct rtmsg *rt;
-	char data[NLMSG_ALIGN(sizeof(*nh)) +
-		  NLMSG_ALIGN(sizeof(*rt)) +
-		  NLMSG_ALIGN(RTA_LENGTH(sizeof(addr6))) +
-		  NLMSG_ALIGN(RTA_LENGTH(sizeof(int))) +
-		  NLMSG_ALIGN(RTA_LENGTH(0) + RTA_LENGTH(sizeof(int)))];
-	int fd, ret, alen, off = 0;
-
-	alen = is_ipv4 ? sizeof(addr4) : sizeof(addr6);
-
-	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
-	if (fd == -1)
-		error(1, errno, "socket netlink");
-
-	memset(data, 0, sizeof(data));
-
-	nh = (void *)data;
-	nh->nlmsg_type = RTM_NEWROUTE;
-	nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
-	off += NLMSG_ALIGN(sizeof(*nh));
-
-	rt = (void *)(data + off);
-	rt->rtm_family = is_ipv4 ? AF_INET : AF_INET6;
-	rt->rtm_table = RT_TABLE_MAIN;
-	rt->rtm_dst_len = alen << 3;
-	rt->rtm_protocol = RTPROT_BOOT;
-	rt->rtm_scope = RT_SCOPE_UNIVERSE;
-	rt->rtm_type = RTN_UNICAST;
-	off += NLMSG_ALIGN(sizeof(*rt));
-
-	rta = (void *)(data + off);
-	rta->rta_type = RTA_DST;
-	rta->rta_len = RTA_LENGTH(alen);
-	if (is_ipv4)
-		memcpy(RTA_DATA(rta), &addr4, alen);
-	else
-		memcpy(RTA_DATA(rta), &addr6, alen);
-	off += NLMSG_ALIGN(rta->rta_len);
-
-	rta = (void *)(data + off);
-	rta->rta_type = RTA_OIF;
-	rta->rta_len = RTA_LENGTH(sizeof(int));
-	*((int *)(RTA_DATA(rta))) = 1; //if_nametoindex("lo");
-	off += NLMSG_ALIGN(rta->rta_len);
-
-	/* MTU is a subtype in a metrics type */
-	rta = (void *)(data + off);
-	rta->rta_type = RTA_METRICS;
-	rta->rta_len = RTA_LENGTH(0) + RTA_LENGTH(sizeof(int));
-	off += NLMSG_ALIGN(rta->rta_len);
-
-	/* now fill MTU subtype. Note that it fits within above rta_len */
-	rta = (void *)(((char *) rta) + RTA_LENGTH(0));
-	rta->rta_type = RTAX_MTU;
-	rta->rta_len = RTA_LENGTH(sizeof(int));
-	*((int *)(RTA_DATA(rta))) = mtu;
-
-	nh->nlmsg_len = off;
-
-	ret = sendto(fd, data, off, 0, (void *)&nladdr, sizeof(nladdr));
-	if (ret != off)
-		error(1, errno, "send netlink: %uB != %uB\n", ret, off);
-
-	if (close(fd))
-		error(1, errno, "close netlink");
-
-	fprintf(stderr, "route mtu (test): %u\n", mtu);
-}
-
 static bool __send_one(int fd, struct msghdr *msg, int flags)
 {
 	int ret;
@@ -591,15 +478,10 @@ static void run_test(struct sockaddr *addr, socklen_t alen)
 	/* Do not fragment these datagrams: only succeed if GSO works */
 	set_pmtu_discover(fdt, addr->sa_family == AF_INET);
 
-	if (cfg_do_connectionless) {
-		set_device_mtu(fdt, CONST_MTU_TEST);
+	if (cfg_do_connectionless)
 		run_all(fdt, fdr, addr, alen);
-	}
 
 	if (cfg_do_connected) {
-		set_device_mtu(fdt, CONST_MTU_TEST + 100);
-		set_route_mtu(CONST_MTU_TEST, addr->sa_family == AF_INET);
-
 		if (connect(fdt, addr, alen))
 			error(1, errno, "connect");
 
diff --git a/tools/testing/selftests/net/udpgso.sh b/tools/testing/selftests/net/udpgso.sh
index fec24f584fe9..d7fb71e132bb 100755
--- a/tools/testing/selftests/net/udpgso.sh
+++ b/tools/testing/selftests/net/udpgso.sh
@@ -3,27 +3,57 @@
 #
 # Run a series of udpgso regression tests
 
+set -o errexit
+set -o nounset
+# set -o xtrace
+
+setup_loopback() {
+  ip addr add dev lo 192.0.2.1/32
+  ip addr add dev lo 2001:db8::1/128 nodad noprefixroute
+}
+
+test_dev_mtu() {
+  setup_loopback
+  # Reduce loopback MTU
+  ip link set dev lo mtu 1500
+}
+
+test_route_mtu() {
+  setup_loopback
+  # Remove default local routes
+  ip route del local 192.0.2.1/32 table local dev lo
+  ip route del local 2001:db8::1/128 table local dev lo
+  # Install local routes with reduced MTU
+  ip route add local 192.0.2.1/32 table local dev lo mtu 1500
+  ip route add local 2001:db8::1/128 table local dev lo mtu 1500
+}
+
+if [ "$#" -gt 0 ]; then
+  "$1"
+  shift 2 # pop "test_*" function arg and "--" delimiter
+  exec "$@"
+fi
+
 echo "ipv4 cmsg"
-./in_netns.sh ./udpgso -4 -C
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C
 
 echo "ipv4 setsockopt"
-./in_netns.sh ./udpgso -4 -C -s
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C -s
 
 echo "ipv6 cmsg"
-./in_netns.sh ./udpgso -6 -C
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C
 
 echo "ipv6 setsockopt"
-./in_netns.sh ./udpgso -6 -C -s
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C -s
 
 echo "ipv4 connected"
-./in_netns.sh ./udpgso -4 -c
+./in_netns.sh "$0" test_route_mtu -- ./udpgso -4 -c
 
-# blocked on 2nd loopback address
-# echo "ipv6 connected"
-# ./in_netns.sh ./udpgso -6 -c
+echo "ipv6 connected"
+./in_netns.sh "$0" test_route_mtu -- ./udpgso -6 -c
 
 echo "ipv4 msg_more"
-./in_netns.sh ./udpgso -4 -C -m
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C -m
 
 echo "ipv6 msg_more"
-./in_netns.sh ./udpgso -6 -C -m
+./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C -m
-- 
2.43.0

Re: [PATCH net-next] selftests: udpgso: Pull up network setup into shell script

[Willem de Bruijn]

Jakub Sitnicki wrote:
> udpgso regression test configures routing and device MTU directly through
> uAPI (Netlink, ioctl) to do its job. While there is nothing wrong with it,
> it takes more effort than doing it from shell.
> 
> Looking forward, we would like to extend the udpgso regression tests to
> cover the EIO corner case [1], once it gets addressed. That will require a
> dummy device and device feature manipulation to set it up. Which means more
> Netlink code.
> 
> So, in preparation, pull out network configuration into the shell script
> part of the test, so it is easily extendable in the future.
> 
> Also, because it now easy to setup routing, add a second local IPv6
> address. Because the second address is not managed by the kernel, we can
> "replace" the corresponding local route with a reduced-MTU one. This
> unblocks the disabled "ipv6 connected" test case. Add a similar setup for
> IPv4 for symmetry.

Nice!

Just a few small nits.

> 
> [1] https://lore.kernel.org/netdev/87jzqsld6q.fsf@cloudflare.com/
> 
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
>  tools/testing/selftests/net/udpgso.c  | 134 ++------------------------
>  tools/testing/selftests/net/udpgso.sh |  50 ++++++++--
>  2 files changed, 48 insertions(+), 136 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/udpgso.c b/tools/testing/selftests/net/udpgso.c
> index 7badaf215de2..79fd3287ff60 100644
> --- a/tools/testing/selftests/net/udpgso.c
> +++ b/tools/testing/selftests/net/udpgso.c
> @@ -56,7 +56,6 @@ static bool		cfg_do_msgmore;
>  static bool		cfg_do_setsockopt;
>  static int		cfg_specific_test_id = -1;
>  
> -static const char	cfg_ifname[] = "lo";
>  static unsigned short	cfg_port = 9000;
>  
>  static char buf[ETH_MAX_MTU];
> @@ -69,8 +68,13 @@ struct testcase {
>  	int r_len_last;		/* recv(): size of last non-mss dgram, if any */
>  };
>  
> -const struct in6_addr addr6 = IN6ADDR_LOOPBACK_INIT;
> -const struct in_addr addr4 = { .s_addr = __constant_htonl(INADDR_LOOPBACK + 2) };
> +const struct in6_addr addr6 = {
> +	{ { 0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x01 } },
> +};
> +
> +const struct in_addr addr4 = {
> +	__constant_htonl(0xc0000201), /* 192.0.2.1 */
> +};

Prefer an address from a private range?

>  struct testcase testcases_v4[] = {
>  	{
> @@ -274,48 +278,6 @@ struct testcase testcases_v6[] = {
>  	}
>  };
>  
> -static unsigned int get_device_mtu(int fd, const char *ifname)
> -{
> -	struct ifreq ifr;
> -
> -	memset(&ifr, 0, sizeof(ifr));
> -
> -	strcpy(ifr.ifr_name, ifname);
> -
> -	if (ioctl(fd, SIOCGIFMTU, &ifr))
> -		error(1, errno, "ioctl get mtu");
> -
> -	return ifr.ifr_mtu;
> -}
> -
> -static void __set_device_mtu(int fd, const char *ifname, unsigned int mtu)
> -{
> -	struct ifreq ifr;
> -
> -	memset(&ifr, 0, sizeof(ifr));
> -
> -	ifr.ifr_mtu = mtu;
> -	strcpy(ifr.ifr_name, ifname);
> -
> -	if (ioctl(fd, SIOCSIFMTU, &ifr))
> -		error(1, errno, "ioctl set mtu");
> -}
> -
> -static void set_device_mtu(int fd, int mtu)
> -{
> -	int val;
> -
> -	val = get_device_mtu(fd, cfg_ifname);
> -	fprintf(stderr, "device mtu (orig): %u\n", val);
> -
> -	__set_device_mtu(fd, cfg_ifname, mtu);
> -	val = get_device_mtu(fd, cfg_ifname);
> -	if (val != mtu)
> -		error(1, 0, "unable to set device mtu to %u\n", val);
> -
> -	fprintf(stderr, "device mtu (test): %u\n", val);
> -}
> -
>  static void set_pmtu_discover(int fd, bool is_ipv4)
>  {
>  	int level, name, val;
> @@ -354,81 +316,6 @@ static unsigned int get_path_mtu(int fd, bool is_ipv4)
>  	return mtu;
>  }
>  
> -/* very wordy version of system("ip route add dev lo mtu 1500 127.0.0.3/32") */
> -static void set_route_mtu(int mtu, bool is_ipv4)
> -{
> -	struct sockaddr_nl nladdr = { .nl_family = AF_NETLINK };
> -	struct nlmsghdr *nh;
> -	struct rtattr *rta;
> -	struct rtmsg *rt;
> -	char data[NLMSG_ALIGN(sizeof(*nh)) +
> -		  NLMSG_ALIGN(sizeof(*rt)) +
> -		  NLMSG_ALIGN(RTA_LENGTH(sizeof(addr6))) +
> -		  NLMSG_ALIGN(RTA_LENGTH(sizeof(int))) +
> -		  NLMSG_ALIGN(RTA_LENGTH(0) + RTA_LENGTH(sizeof(int)))];
> -	int fd, ret, alen, off = 0;
> -
> -	alen = is_ipv4 ? sizeof(addr4) : sizeof(addr6);
> -
> -	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
> -	if (fd == -1)
> -		error(1, errno, "socket netlink");
> -
> -	memset(data, 0, sizeof(data));
> -
> -	nh = (void *)data;
> -	nh->nlmsg_type = RTM_NEWROUTE;
> -	nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
> -	off += NLMSG_ALIGN(sizeof(*nh));
> -
> -	rt = (void *)(data + off);
> -	rt->rtm_family = is_ipv4 ? AF_INET : AF_INET6;
> -	rt->rtm_table = RT_TABLE_MAIN;
> -	rt->rtm_dst_len = alen << 3;
> -	rt->rtm_protocol = RTPROT_BOOT;
> -	rt->rtm_scope = RT_SCOPE_UNIVERSE;
> -	rt->rtm_type = RTN_UNICAST;
> -	off += NLMSG_ALIGN(sizeof(*rt));
> -
> -	rta = (void *)(data + off);
> -	rta->rta_type = RTA_DST;
> -	rta->rta_len = RTA_LENGTH(alen);
> -	if (is_ipv4)
> -		memcpy(RTA_DATA(rta), &addr4, alen);
> -	else
> -		memcpy(RTA_DATA(rta), &addr6, alen);
> -	off += NLMSG_ALIGN(rta->rta_len);
> -
> -	rta = (void *)(data + off);
> -	rta->rta_type = RTA_OIF;
> -	rta->rta_len = RTA_LENGTH(sizeof(int));
> -	*((int *)(RTA_DATA(rta))) = 1; //if_nametoindex("lo");
> -	off += NLMSG_ALIGN(rta->rta_len);
> -
> -	/* MTU is a subtype in a metrics type */
> -	rta = (void *)(data + off);
> -	rta->rta_type = RTA_METRICS;
> -	rta->rta_len = RTA_LENGTH(0) + RTA_LENGTH(sizeof(int));
> -	off += NLMSG_ALIGN(rta->rta_len);
> -
> -	/* now fill MTU subtype. Note that it fits within above rta_len */
> -	rta = (void *)(((char *) rta) + RTA_LENGTH(0));
> -	rta->rta_type = RTAX_MTU;
> -	rta->rta_len = RTA_LENGTH(sizeof(int));
> -	*((int *)(RTA_DATA(rta))) = mtu;
> -
> -	nh->nlmsg_len = off;
> -
> -	ret = sendto(fd, data, off, 0, (void *)&nladdr, sizeof(nladdr));
> -	if (ret != off)
> -		error(1, errno, "send netlink: %uB != %uB\n", ret, off);
> -
> -	if (close(fd))
> -		error(1, errno, "close netlink");
> -
> -	fprintf(stderr, "route mtu (test): %u\n", mtu);
> -}
> -

Oh no, my handcrafted artisanal netlink code!

Yeah, concise shell commands are a better model.

>  static bool __send_one(int fd, struct msghdr *msg, int flags)
>  {
>  	int ret;
> @@ -591,15 +478,10 @@ static void run_test(struct sockaddr *addr, socklen_t alen)
>  	/* Do not fragment these datagrams: only succeed if GSO works */
>  	set_pmtu_discover(fdt, addr->sa_family == AF_INET);
>  
> -	if (cfg_do_connectionless) {
> -		set_device_mtu(fdt, CONST_MTU_TEST);
> +	if (cfg_do_connectionless)
>  		run_all(fdt, fdr, addr, alen);
> -	}
>  
>  	if (cfg_do_connected) {
> -		set_device_mtu(fdt, CONST_MTU_TEST + 100);
> -		set_route_mtu(CONST_MTU_TEST, addr->sa_family == AF_INET);
> -
>  		if (connect(fdt, addr, alen))
>  			error(1, errno, "connect");
>  
> diff --git a/tools/testing/selftests/net/udpgso.sh b/tools/testing/selftests/net/udpgso.sh
> index fec24f584fe9..d7fb71e132bb 100755
> --- a/tools/testing/selftests/net/udpgso.sh
> +++ b/tools/testing/selftests/net/udpgso.sh
> @@ -3,27 +3,57 @@
>  #
>  # Run a series of udpgso regression tests
>  
> +set -o errexit
> +set -o nounset
> +# set -o xtrace

Leftover debug comment?

> +
> +setup_loopback() {
> +  ip addr add dev lo 192.0.2.1/32
> +  ip addr add dev lo 2001:db8::1/128 nodad noprefixroute
> +}
> +
> +test_dev_mtu() {
> +  setup_loopback
> +  # Reduce loopback MTU
> +  ip link set dev lo mtu 1500
> +}
> +
> +test_route_mtu() {
> +  setup_loopback
> +  # Remove default local routes
> +  ip route del local 192.0.2.1/32 table local dev lo
> +  ip route del local 2001:db8::1/128 table local dev lo
> +  # Install local routes with reduced MTU
> +  ip route add local 192.0.2.1/32 table local dev lo mtu 1500
> +  ip route add local 2001:db8::1/128 table local dev lo mtu 1500

ip route change?

> +}
> +
> +if [ "$#" -gt 0 ]; then
> +  "$1"
> +  shift 2 # pop "test_*" function arg and "--" delimiter
> +  exec "$@"
> +fi
> +
>  echo "ipv4 cmsg"
> -./in_netns.sh ./udpgso -4 -C
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C
>  
>  echo "ipv4 setsockopt"
> -./in_netns.sh ./udpgso -4 -C -s
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C -s
>  
>  echo "ipv6 cmsg"
> -./in_netns.sh ./udpgso -6 -C
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C
>  
>  echo "ipv6 setsockopt"
> -./in_netns.sh ./udpgso -6 -C -s
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C -s
>  
>  echo "ipv4 connected"
> -./in_netns.sh ./udpgso -4 -c
> +./in_netns.sh "$0" test_route_mtu -- ./udpgso -4 -c
>  
> -# blocked on 2nd loopback address
> -# echo "ipv6 connected"
> -# ./in_netns.sh ./udpgso -6 -c
> +echo "ipv6 connected"
> +./in_netns.sh "$0" test_route_mtu -- ./udpgso -6 -c
>  
>  echo "ipv4 msg_more"
> -./in_netns.sh ./udpgso -4 -C -m
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -4 -C -m
>  
>  echo "ipv6 msg_more"
> -./in_netns.sh ./udpgso -6 -C -m
> +./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C -m
> -- 
> 2.43.0
> 

Re: [PATCH net-next] selftests: udpgso: Pull up network setup into shell script

[Jakub Sitnicki]

On Tue, Jan 30, 2024 at 03:26 PM -05, Willem de Bruijn wrote:
> Jakub Sitnicki wrote:
>> udpgso regression test configures routing and device MTU directly through
>> uAPI (Netlink, ioctl) to do its job. While there is nothing wrong with it,
>> it takes more effort than doing it from shell.
>> 
>> Looking forward, we would like to extend the udpgso regression tests to
>> cover the EIO corner case [1], once it gets addressed. That will require a
>> dummy device and device feature manipulation to set it up. Which means more
>> Netlink code.
>> 
>> So, in preparation, pull out network configuration into the shell script
>> part of the test, so it is easily extendable in the future.
>> 
>> Also, because it now easy to setup routing, add a second local IPv6
>> address. Because the second address is not managed by the kernel, we can
>> "replace" the corresponding local route with a reduced-MTU one. This
>> unblocks the disabled "ipv6 connected" test case. Add a similar setup for
>> IPv4 for symmetry.
>
> Nice!
>
> Just a few small nits.
>

Thanks for quick feedback. Will apply it and respin.

>> 
>> [1] https://lore.kernel.org/netdev/87jzqsld6q.fsf@cloudflare.com/
>> 
>> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
>> ---
>>  tools/testing/selftests/net/udpgso.c  | 134 ++------------------------
>>  tools/testing/selftests/net/udpgso.sh |  50 ++++++++--
>>  2 files changed, 48 insertions(+), 136 deletions(-)
>> 
>> diff --git a/tools/testing/selftests/net/udpgso.c b/tools/testing/selftests/net/udpgso.c
>> index 7badaf215de2..79fd3287ff60 100644
>> --- a/tools/testing/selftests/net/udpgso.c
>> +++ b/tools/testing/selftests/net/udpgso.c
>> @@ -56,7 +56,6 @@ static bool		cfg_do_msgmore;
>>  static bool		cfg_do_setsockopt;
>>  static int		cfg_specific_test_id = -1;
>>  
>> -static const char	cfg_ifname[] = "lo";
>>  static unsigned short	cfg_port = 9000;
>>  
>>  static char buf[ETH_MAX_MTU];
>> @@ -69,8 +68,13 @@ struct testcase {
>>  	int r_len_last;		/* recv(): size of last non-mss dgram, if any */
>>  };
>>  
>> -const struct in6_addr addr6 = IN6ADDR_LOOPBACK_INIT;
>> -const struct in_addr addr4 = { .s_addr = __constant_htonl(INADDR_LOOPBACK + 2) };
>> +const struct in6_addr addr6 = {
>> +	{ { 0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x01 } },
>> +};
>> +
>> +const struct in_addr addr4 = {
>> +	__constant_htonl(0xc0000201), /* 192.0.2.1 */
>> +};
>
> Prefer an address from a private range?

No preference. I saw both in use across net selftests and went with one.

[...]

>> diff --git a/tools/testing/selftests/net/udpgso.sh b/tools/testing/selftests/net/udpgso.sh
>> index fec24f584fe9..d7fb71e132bb 100755
>> --- a/tools/testing/selftests/net/udpgso.sh
>> +++ b/tools/testing/selftests/net/udpgso.sh
>> @@ -3,27 +3,57 @@
>>  #
>>  # Run a series of udpgso regression tests
>>  
>> +set -o errexit
>> +set -o nounset
>> +# set -o xtrace
>
> Leftover debug comment?
>

Left it on purpose for the next person debugging it. But can remove it.

>> +
>> +setup_loopback() {
>> +  ip addr add dev lo 192.0.2.1/32
>> +  ip addr add dev lo 2001:db8::1/128 nodad noprefixroute
>> +}
>> +
>> +test_dev_mtu() {
>> +  setup_loopback
>> +  # Reduce loopback MTU
>> +  ip link set dev lo mtu 1500
>> +}
>> +
>> +test_route_mtu() {
>> +  setup_loopback
>> +  # Remove default local routes
>> +  ip route del local 192.0.2.1/32 table local dev lo
>> +  ip route del local 2001:db8::1/128 table local dev lo
>> +  # Install local routes with reduced MTU
>> +  ip route add local 192.0.2.1/32 table local dev lo mtu 1500
>> +  ip route add local 2001:db8::1/128 table local dev lo mtu 1500
>
> ip route change?
>

I've tried it. Doesn't work as expected. Only del+add seems do to
it. You end up with two routes if you use `ip route replace`:

  # ip route replace local 2001:db8::1/128 table local dev lo mtu 1500
  # ip -6 route show table local
  local ::1 dev lo proto kernel metric 0 pref medium
  local 2001:db8::1 dev lo proto kernel metric 0 pref medium
  local 2001:db8::1 dev lo metric 1024 mtu 1500 pref medium
  #

I didn't dig into why, though.

[...]