From 00ed2fff1a87372e6af37398f48527d75c00339c Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 16 Nov 2020 12:41:23 +0100
Subject: [PATCH 1/3] socket-util: add sockopt helper for controlling
 IP_RECVFRAGSIZE

---
 src/basic/missing_socket.h | 8 ++++++++
 src/basic/socket-util.h    | 4 ++++
 2 files changed, 12 insertions(+)

diff --git a/src/basic/missing_socket.h b/src/basic/missing_socket.h
index 17bc1a5a01..30ac297e17 100644
--- a/src/basic/missing_socket.h
+++ b/src/basic/missing_socket.h
@@ -67,6 +67,14 @@ struct sockaddr_vm {
 #define IPV6_FREEBIND 78
 #endif
 
+#ifndef IP_RECVFRAGSIZE
+#define IP_RECVFRAGSIZE 25
+#endif
+
+#ifndef IPV6_RECVFRAGSIZE
+#define IPV6_RECVFRAGSIZE 77
+#endif
+
 /* linux/sockios.h */
 #ifndef SIOCGSKNS
 #define SIOCGSKNS 0x894C
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index e353f82a42..7d77144f43 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -266,6 +266,7 @@ ssize_t recvmsg_safe(int sockfd, struct msghdr *msg, int flags);
 int socket_get_family(int fd, int *ret);
 int socket_set_recvpktinfo(int fd, int af, bool b);
 int socket_set_unicast_if(int fd, int af, int ifi);
+
 int socket_set_option(int fd, int af, int opt_ipv4, int opt_ipv6, int val);
 static inline int socket_set_recverr(int fd, int af, bool b) {
         return socket_set_option(fd, af, IP_RECVERR, IPV6_RECVERR, b);
@@ -282,3 +283,6 @@ static inline int socket_set_freebind(int fd, int af, bool b) {
 static inline int socket_set_transparent(int fd, int af, bool b) {
         return socket_set_option(fd, af, IP_TRANSPARENT, IPV6_TRANSPARENT, b);
 }
+static inline int socket_set_recvfragsize(int fd, int af, bool b) {
+        return socket_set_option(fd, af, IP_RECVFRAGSIZE, IPV6_RECVFRAGSIZE, b);
+}

From 4e25d4cf0f78ef7c960f2b77c941e3d8751535df Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 16 Nov 2020 12:41:39 +0100
Subject: [PATCH 2/3] socket-util: add getsockopt_int() helper

---
 src/basic/socket-util.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 7d77144f43..0dd6798d32 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -258,6 +258,19 @@ static inline int setsockopt_int(int fd, int level, int optname, int value) {
         return 0;
 }
 
+static inline int getsockopt_int(int fd, int level, int optname, int *ret) {
+        int v;
+        socklen_t sl = sizeof(v);
+
+        if (getsockopt(fd, level, optname, &v, &sl) < 0)
+                return -errno;
+        if (sl != sizeof(v))
+                return -EIO;
+
+        *ret = v;
+        return 0;
+}
+
 int socket_bind_to_ifname(int fd, const char *ifname);
 int socket_bind_to_ifindex(int fd, int ifindex);
 

From 52975f86721e4f1c612dbf39f92a590edcea2b72 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 16 Nov 2020 15:01:03 +0100
Subject: [PATCH 3/3] socket-util: add common API for querying socket MTU

---
 src/basic/socket-util.c | 32 ++++++++++++++++++++++++++++++++
 src/basic/socket-util.h |  2 ++
 2 files changed, 34 insertions(+)

diff --git a/src/basic/socket-util.c b/src/basic/socket-util.c
index 1e53ac4e86..59039bea4f 100644
--- a/src/basic/socket-util.c
+++ b/src/basic/socket-util.c
@@ -1314,3 +1314,35 @@ int socket_set_option(int fd, int af, int opt_ipv4, int opt_ipv6, int val) {
                 return -EAFNOSUPPORT;
         }
 }
+
+int socket_get_mtu(int fd, int af, size_t *ret) {
+        int mtu, r;
+
+        if (af == AF_UNSPEC) {
+                r = socket_get_family(fd, &af);
+                if (r < 0)
+                        return r;
+        }
+
+        switch (af) {
+
+        case AF_INET:
+                r = getsockopt_int(fd, IPPROTO_IP, IP_MTU, &mtu);
+                break;
+
+        case AF_INET6:
+                r = getsockopt_int(fd, IPPROTO_IPV6, IPV6_MTU, &mtu);
+                break;
+
+        default:
+                return -EAFNOSUPPORT;
+        }
+
+        if (r < 0)
+                return r;
+        if (mtu <= 0)
+                return -EINVAL;
+
+        *ret = (size_t) mtu;
+        return 0;
+}
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 0dd6798d32..240d209c14 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -299,3 +299,5 @@ static inline int socket_set_transparent(int fd, int af, bool b) {
 static inline int socket_set_recvfragsize(int fd, int af, bool b) {
         return socket_set_option(fd, af, IP_RECVFRAGSIZE, IPV6_RECVFRAGSIZE, b);
 }
+
+int socket_get_mtu(int fd, int af, size_t *ret);