[socket-nif] Add support for socket (level socket) option(s) [rcv|snd]lowat

Added support for socket level socket option RCVLOWAT and SNDLOWAT.
These are both a little strange, at least on Linux. See the man
pages for more info. For instance, sndlowat cannot be set on Linux.

OTP-14831

4 files changed, 111 insertions, 7 deletions

diff --git a/erts/doc/src/socket_usage.xml b/erts/doc/src/socket_usage.xml
index 221561c3e2..9ea585694d 100644
--- a/erts/doc/src/socket_usage.xml
+++ b/erts/doc/src/socket_usage.xml
@@ -180,6 +180,13 @@
 	<cell>none</cell>
       </row>
       <row>
+	<cell>rcvlowat</cell>
+	<cell>non_neg_integer()</cell>
+	<cell>yes</cell>
+	<cell>yes</cell>
+	<cell>none</cell>
+      </row>
+      <row>
 	<cell>rcvtimeo</cell>
 	<cell>timeval()</cell>
 	<cell>yes</cell>
@@ -202,12 +209,19 @@
       </row>
       <row>
 	<cell>sndbuf</cell>
-	<cell>integer()</cell>
+	<cell>non_neg_integer()</cell>
 	<cell>yes</cell>
 	<cell>yes</cell>
 	<cell>none</cell>
       </row>
       <row>
+	<cell>sndlowat</cell>
+	<cell>non_neg_integer()</cell>
+	<cell>yes</cell>
+	<cell>yes</cell>
+	<cell>not changeable on Linux</cell>
+      </row>
+      <row>
 	<cell>sndtimeo</cell>
 	<cell>timeval()</cell>
 	<cell>yes</cell>
diff --git a/erts/emulator/nifs/common/socket_nif.c b/erts/emulator/nifs/common/socket_nif.c
index 53122ab957..365cbd541b 100644
--- a/erts/emulator/nifs/common/socket_nif.c
+++ b/erts/emulator/nifs/common/socket_nif.c
@@ -502,10 +502,12 @@ typedef union {
 #define SOCKET_OPT_SOCK_PRIORITY      17
 #define SOCKET_OPT_SOCK_PROTOCOL      18
 #define SOCKET_OPT_SOCK_RCVBUF        19
+#define SOCKET_OPT_SOCK_RCVLOWAT      21
 #define SOCKET_OPT_SOCK_RCVTIMEO      22
 #define SOCKET_OPT_SOCK_REUSEADDR     23
 #define SOCKET_OPT_SOCK_REUSEPORT     24
 #define SOCKET_OPT_SOCK_SNDBUF        27
+#define SOCKET_OPT_SOCK_SNDLOWAT      29
 #define SOCKET_OPT_SOCK_SNDTIMEO      30
 #define SOCKET_OPT_SOCK_TYPE          32
 
@@ -1012,6 +1014,11 @@ static ERL_NIF_TERM nsetopt_lvl_sock_rcvbuf(ErlNifEnv*        env,
                                             SocketDescriptor* descP,
                                             ERL_NIF_TERM      eVal);
 #endif
+#if defined(SO_RCVLOWAT)
+static ERL_NIF_TERM nsetopt_lvl_sock_rcvlowat(ErlNifEnv*        env,
+                                              SocketDescriptor* descP,
+                                              ERL_NIF_TERM      eVal);
+#endif
 #if defined(SO_RCVTIMEO)
 static ERL_NIF_TERM nsetopt_lvl_sock_rcvtimeo(ErlNifEnv*        env,
                                               SocketDescriptor* descP,
@@ -1032,6 +1039,11 @@ static ERL_NIF_TERM nsetopt_lvl_sock_sndbuf(ErlNifEnv*        env,
                                             SocketDescriptor* descP,
                                             ERL_NIF_TERM      eVal);
 #endif
+#if defined(SO_SNDLOWAT)
+static ERL_NIF_TERM nsetopt_lvl_sock_sndlowat(ErlNifEnv*        env,
+                                              SocketDescriptor* descP,
+                                              ERL_NIF_TERM      eVal);
+#endif
 #if defined(SO_SNDTIMEO)
 static ERL_NIF_TERM nsetopt_lvl_sock_sndtimeo(ErlNifEnv*        env,
                                               SocketDescriptor* descP,
@@ -1351,6 +1363,10 @@ static ERL_NIF_TERM ngetopt_lvl_sock_protocol(ErlNifEnv*        env,
 static ERL_NIF_TERM ngetopt_lvl_sock_rcvbuf(ErlNifEnv*        env,
                                             SocketDescriptor* descP);
 #endif
+#if defined(SO_RCVLOWAT)
+static ERL_NIF_TERM ngetopt_lvl_sock_rcvlowat(ErlNifEnv*        env,
+                                              SocketDescriptor* descP);
+#endif
 #if defined(SO_RCVTIMEO)
 static ERL_NIF_TERM ngetopt_lvl_sock_rcvtimeo(ErlNifEnv*        env,
                                               SocketDescriptor* descP);
@@ -1367,6 +1383,10 @@ static ERL_NIF_TERM ngetopt_lvl_sock_reuseport(ErlNifEnv*        env,
 static ERL_NIF_TERM ngetopt_lvl_sock_sndbuf(ErlNifEnv*        env,
                                             SocketDescriptor* descP);
 #endif
+#if defined(SO_SNDLOWAT)
+static ERL_NIF_TERM ngetopt_lvl_sock_sndlowat(ErlNifEnv*        env,
+                                              SocketDescriptor* descP);
+#endif
 #if defined(SO_SNDTIMEO)
 static ERL_NIF_TERM ngetopt_lvl_sock_sndtimeo(ErlNifEnv*        env,
                                               SocketDescriptor* descP);
@@ -4379,6 +4399,12 @@ ERL_NIF_TERM nsetopt_lvl_socket(ErlNifEnv*        env,
         break;
 #endif
 
+#if defined(SO_RCVLOWAT)
+    case SOCKET_OPT_SOCK_RCVLOWAT:
+        result = nsetopt_lvl_sock_rcvlowat(env, descP, eVal);
+        break;
+#endif
+
 #if defined(SO_RCVTIMEO)
     case SOCKET_OPT_SOCK_RCVTIMEO:
         result = nsetopt_lvl_sock_rcvtimeo(env, descP, eVal);
@@ -4403,6 +4429,12 @@ ERL_NIF_TERM nsetopt_lvl_socket(ErlNifEnv*        env,
         break;
 #endif
 
+#if defined(SO_SNDLOWAT)
+    case SOCKET_OPT_SOCK_SNDLOWAT:
+        result = nsetopt_lvl_sock_sndlowat(env, descP, eVal);
+        break;
+#endif
+
 #if defined(SO_SNDTIMEO)
     case SOCKET_OPT_SOCK_SNDTIMEO:
         result = nsetopt_lvl_sock_sndtimeo(env, descP, eVal);
@@ -4550,6 +4582,17 @@ ERL_NIF_TERM nsetopt_lvl_sock_rcvbuf(ErlNifEnv*        env,
 #endif
 
 
+#if defined(SO_RCVLOWAT)
+static
+ERL_NIF_TERM nsetopt_lvl_sock_rcvlowat(ErlNifEnv*        env,
+                                     SocketDescriptor* descP,
+                                     ERL_NIF_TERM      eVal)
+{
+    return nsetopt_int_opt(env, descP, SOL_SOCKET, SO_RCVLOWAT, eVal);
+}
+#endif
+
+
 #if defined(SO_RCVTIMEO)
 static
 ERL_NIF_TERM nsetopt_lvl_sock_rcvtimeo(ErlNifEnv*        env,
@@ -4594,6 +4637,17 @@ ERL_NIF_TERM nsetopt_lvl_sock_sndbuf(ErlNifEnv*        env,
 #endif
 
 
+#if defined(SO_SNDLOWAT)
+static
+ERL_NIF_TERM nsetopt_lvl_sock_sndlowat(ErlNifEnv*        env,
+                                       SocketDescriptor* descP,
+                                       ERL_NIF_TERM      eVal)
+{
+    return nsetopt_int_opt(env, descP, SOL_SOCKET, SO_SNDLOWAT, eVal);
+}
+#endif
+
+
 #if defined(SO_SNDTIMEO)
 static
 ERL_NIF_TERM nsetopt_lvl_sock_sndtimeo(ErlNifEnv*        env,
@@ -6863,6 +6917,12 @@ ERL_NIF_TERM ngetopt_lvl_socket(ErlNifEnv*        env,
         break;
 #endif
 
+#if defined(SO_RCVLOWAT)
+    case SOCKET_OPT_SOCK_RCVLOWAT:
+        result = ngetopt_lvl_sock_rcvlowat(env, descP);
+        break;
+#endif
+
 #if defined(SO_RCVTIMEO)
     case SOCKET_OPT_SOCK_RCVTIMEO:
         result = ngetopt_lvl_sock_rcvtimeo(env, descP);
@@ -6887,6 +6947,12 @@ ERL_NIF_TERM ngetopt_lvl_socket(ErlNifEnv*        env,
         break;
 #endif
 
+#if defined(SO_SNDLOWAT)
+    case SOCKET_OPT_SOCK_SNDLOWAT:
+        result = ngetopt_lvl_sock_sndlowat(env, descP);
+        break;
+#endif
+
 #if defined(SO_SNDTIMEO)
     case SOCKET_OPT_SOCK_SNDTIMEO:
         result = ngetopt_lvl_sock_sndtimeo(env, descP);
@@ -7140,6 +7206,16 @@ ERL_NIF_TERM ngetopt_lvl_sock_rcvbuf(ErlNifEnv*        env,
 #endif
 
 
+#if defined(SO_RCVLOWAT)
+static
+ERL_NIF_TERM ngetopt_lvl_sock_rcvlowat(ErlNifEnv*        env,
+                                       SocketDescriptor* descP)
+{
+    return ngetopt_int_opt(env, descP, SOL_SOCKET, SO_RCVLOWAT);
+}
+#endif
+
+
 #if defined(SO_RCVTIMEO)
 static
 ERL_NIF_TERM ngetopt_lvl_sock_rcvtimeo(ErlNifEnv*        env,
@@ -7180,6 +7256,16 @@ ERL_NIF_TERM ngetopt_lvl_sock_sndbuf(ErlNifEnv*        env,
 #endif
 
 
+#if defined(SO_SNDLOWAT)
+static
+ERL_NIF_TERM ngetopt_lvl_sock_sndlowat(ErlNifEnv*        env,
+                                       SocketDescriptor* descP)
+{
+    return ngetopt_int_opt(env, descP, SOL_SOCKET, SO_SNDLOWAT);
+}
+#endif
+
+
 #if defined(SO_SNDTIMEO)
 static
 ERL_NIF_TERM ngetopt_lvl_sock_sndtimeo(ErlNifEnv*        env,
diff --git a/erts/preloaded/ebin/socket.beam b/erts/preloaded/ebin/socket.beam
index cd4feb8a46..b8d0e86a20 100644
--- a/erts/preloaded/ebin/socket.beam
+++ b/erts/preloaded/ebin/socket.beam
diff --git a/erts/preloaded/src/socket.erl b/erts/preloaded/src/socket.erl
index 15f9693490..3ccba06f6b 100644
--- a/erts/preloaded/src/socket.erl
+++ b/erts/preloaded/src/socket.erl
@@ -575,7 +575,7 @@
 -define(SOCKET_OPT_SOCK_PROTOCOL,       18).
 -define(SOCKET_OPT_SOCK_RCVBUF,         19).
 %% -define(SOCKET_OPT_SOCK_RCVBUFFORCE,    20).
-%% -define(SOCKET_OPT_SOCK_RCVLOWAT,       21).
+-define(SOCKET_OPT_SOCK_RCVLOWAT,       21).
 -define(SOCKET_OPT_SOCK_RCVTIMEO,       22).
 -define(SOCKET_OPT_SOCK_REUSEADDR,      23).
 -define(SOCKET_OPT_SOCK_REUSEPORT,      24).
@@ -583,7 +583,7 @@
 %% -define(SOCKET_OPT_SOCK_SETFIB,         26).
 -define(SOCKET_OPT_SOCK_SNDBUF,         27).
 %% -define(SOCKET_OPT_SOCK_SNDBUFFORCE,    28).
-%% -define(SOCKET_OPT_SOCK_SNDLOWAT,       29).
+-define(SOCKET_OPT_SOCK_SNDLOWAT,       29).
 -define(SOCKET_OPT_SOCK_SNDTIMEO,       30).
 %% -define(SOCKET_OPT_SOCK_TIMESTAMP,      31).
 -define(SOCKET_OPT_SOCK_TYPE,           32).
@@ -2125,6 +2125,8 @@ enc_setopt_value(socket, priority, V, _D, _T, _P) when is_integer(V) ->
     V;
 enc_setopt_value(socket, rcvbuf, V, _D, _T, _P) when is_integer(V) ->
     V;
+enc_setopt_value(socket, rcvlowat, V, _D, _T, _P) when is_integer(V) ->
+    V;
 enc_setopt_value(socket, rcvtimeo, #{sec := Sec, usec := USec} = V, _D, _T, _P) 
   when is_integer(Sec) andalso is_integer(USec) ->
     V;
@@ -2134,6 +2136,8 @@ enc_setopt_value(socket, reuseport, V, _D, _T, _P) when is_boolean(V) ->
     V;
 enc_setopt_value(socket, sndbuf, V, _D, _T, _P) when is_integer(V) ->
     V;
+enc_setopt_value(socket, sndlowat, V, _D, _T, _P) when is_integer(V) ->
+    V;
 enc_setopt_value(socket, sndtimeo, #{sec := Sec, usec := USec} = V, _D, _T, _P) 
   when is_integer(Sec) andalso is_integer(USec) ->
     V;
@@ -2523,8 +2527,8 @@ enc_sockopt_key(socket, rcvbuf = _Opt, _Dir, _D, _T, _P) ->
 enc_sockopt_key(socket = L, rcvbufforce = Opt, _Dir, _D, _T, _P) ->
     not_supported({L, Opt});
 %% May not work on linux.
-enc_sockopt_key(socket = L, rcvlowat = Opt, _Dir, _D, _T, _P) ->
-    not_supported({L, Opt});
+enc_sockopt_key(socket = _L, rcvlowat = _Opt, _Dir, _D, _T, _P) ->
+    ?SOCKET_OPT_SOCK_RCVLOWAT;
 enc_sockopt_key(socket = _L, rcvtimeo = _Opt, _Dir, _D, _T, _P) ->
     ?SOCKET_OPT_SOCK_RCVTIMEO;
 enc_sockopt_key(socket = _L, reuseaddr = _Opt, _Dir, _D, _T, _P) ->
@@ -2541,8 +2545,8 @@ enc_sockopt_key(socket = _L, sndbuf = _Opt, _Dir, _D, _T, _P) ->
 enc_sockopt_key(socket = L, sndbufforce = Opt, _Dir, _D, _T, _P) ->
     not_supported({L, Opt});
 %% Not changeable on linux.
-enc_sockopt_key(socket = L, sndlowat = Opt, _Dir, _D, _T, _P) ->
-    not_supported({L, Opt});
+enc_sockopt_key(socket = _L, sndlowat = _Opt, _Dir, _D, _T, _P) ->
+    ?SOCKET_OPT_SOCK_SNDLOWAT;
 enc_sockopt_key(socket = _L, sndtimeo = _Opt, _Dir, _D, _T, _P) ->
     ?SOCKET_OPT_SOCK_SNDTIMEO;
 enc_sockopt_key(socket = L, timestamp = Opt, _Dir, _D, _T, _P) ->