From 7f8029301a20c4cf99988a2b6bef30619524c86f Mon Sep 17 00:00:00 2001
From: Francesco Lavra <francescolavra.fl@gmail.com>
Date: Sat, 19 Oct 2024 09:58:09 +0200
Subject: [PATCH] Network socket options: add support for
 IPPROTO_IP/IP_MTU_DISCOVER

This socket option controls the setting of the DF (don't fragment)
flag in output IPv4 packets.
Depends on https://github.com/nanovms/lwip/pull/14.
---
 src/net/netsyscall.c      | 34 ++++++++++++++++++++++++++++++++++
 src/unix/system_structs.h |  1 +
 2 files changed, 35 insertions(+)

diff --git a/src/net/netsyscall.c b/src/net/netsyscall.c
index 13c48e76e..c934ffe21 100755
--- a/src/net/netsyscall.c
+++ b/src/net/netsyscall.c
@@ -412,6 +412,7 @@ static inline s64 lwip_to_errno(s8 err)
     case ERR_RST: return -ECONNRESET;
     case ERR_CLSD: return -ENOTCONN;
     case ERR_ARG: return -EIO;
+    case ERR_MSGSIZE: return -EMSGSIZE;
     }
     return -EINVAL;		/* XXX unknown - check return value */
 }
@@ -2386,6 +2387,24 @@ static sysreturn netsock_setsockopt(struct sock *sock, int level,
     int int_optval;
     sysreturn rv;
     switch (level) {
+    case IPPROTO_IP:
+        switch (optname) {
+        case IP_MTU_DISCOVER:
+            rv = sockopt_copy_from_user(optval, optlen, &int_optval, sizeof(int));
+            if (rv)
+                goto out;
+            if (s->sock.type == SOCK_STREAM) {
+                struct tcp_pcb *tcp_lw = netsock_tcp_get(s);
+                tcp_lw->pmtudisc = int_optval;
+                netsock_tcp_put(tcp_lw);
+            } else {
+                s->info.udp.lw->pmtudisc = int_optval;
+            }
+            break;
+        default:
+            goto unimplemented;
+        }
+        break;
     case IPPROTO_IPV6:
         switch (optname) {
         case IPV6_V6ONLY:
@@ -2696,6 +2715,21 @@ static sysreturn netsock_getsockopt(struct sock *sock, int level,
             goto unimplemented;
         }
         break;
+    case IPPROTO_IP:
+        switch (optname) {
+        case IP_MTU_DISCOVER:
+            if (s->sock.type == SOCK_STREAM) {
+                struct tcp_pcb *tcp_lw = netsock_tcp_get(s);
+                ret_optval.val = tcp_lw->pmtudisc;
+                netsock_tcp_put(tcp_lw);
+            } else {
+                ret_optval.val = s->info.udp.lw->pmtudisc;
+            }
+            break;
+        default:
+            goto unimplemented;
+        }
+        break;
     case IPPROTO_IPV6:
         switch (optname) {
         case IPV6_V6ONLY:
diff --git a/src/unix/system_structs.h b/src/unix/system_structs.h
index f53d3436f..524abb8ee 100644
--- a/src/unix/system_structs.h
+++ b/src/unix/system_structs.h
@@ -863,6 +863,7 @@ struct io_uring_params {
 #define IP_TOS              1
 #define IP_TTL              2
 #define IP_OPTIONS          4
+#define IP_MTU_DISCOVER     10
 #define IP_MINTTL           21
 #define IP_MULTICAST_IF     32
 #define IP_MULTICAST_TTL    33