kmc-solid: Implement FileDesc::duplicate

library/std/src/sys/solid/abi/sockets.rs

@@ -175,6 +175,9 @@ pub struct fd_set {
     #[link_name = "SOLID_NET_Close"]
     pub fn close(s: c_int) -> c_int;
 
+    #[link_name = "SOLID_NET_Dup"]
+    pub fn dup(s: c_int) -> c_int;
+
     #[link_name = "SOLID_NET_GetPeerName"]
     pub fn getpeername(s: c_int, name: *mut sockaddr, namelen: *mut socklen_t) -> c_int;
 

library/std/src/sys/solid/net.rs

@@ -107,7 +107,7 @@ fn is_write_vectored(&self) -> bool {
     }
 
     fn duplicate(&self) -> io::Result<FileDesc> {
-        super::unsupported()
+        cvt(unsafe { netc::dup(self.fd) }).map(Self::new)
     }
 }