Fix returned error from gen_tcp:accept/1,2 when running out of ports

The {error, enfile} return value is badly misleading and confusing for
this case, since the Posix ENFILE errno value has a well-defined meaning
that has nothing to do with Erlang ports. The fix changes the return
value to {error, system_limit}, which is consistent with e.g. various
file(3) functions. inet:format_error/1 has also been updated to support
system_limit in the same manner as file:format_error/1.

7 files changed, 83 insertions, 24 deletions

diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index 49cd0e5f53..f5a58f9dac 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -743,7 +743,7 @@ driver_create_port(ErlDrvPort creator_port_ix, /* Creating port */
 	return (ErlDrvTermData) -1;   /* pid does not exist */
     }
     if ((port_num = get_free_port()) < 0) {
-	errno = ENFILE;
+	errno = SYSTEM_LIMIT;
 	erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
 	erts_smp_mtx_unlock(&erts_driver_list_lock);
 	return (ErlDrvTermData) -1;
diff --git a/erts/emulator/drivers/common/inet_drv.c b/erts/emulator/drivers/common/inet_drv.c
index eeaa4d24ea..7cee4cb928 100644
--- a/erts/emulator/drivers/common/inet_drv.c
+++ b/erts/emulator/drivers/common/inet_drv.c
@@ -553,6 +553,12 @@ static int my_strncasecmp(const char *s1, const char *s2, size_t n)
 #  define VALGRIND_MAKE_MEM_DEFINED(ptr,size)
 #endif
 
+/*
+  Magic errno value used locally for return of {error, system_limit}
+  - the emulator definition of SYSTEM_LIMIT is not available here.
+*/
+#define INET_ERRNO_SYSTEM_LIMIT  (15 << 8)
+
 /*----------------------------------------------------------------------------
 ** Interface constants.
 ** 
@@ -1645,6 +1651,17 @@ static struct erl_drv_entry dummy_sctp_driver_entry =
 
 #endif
 
+/* return lowercase string form of errno value */
+static char *errno_str(int err)
+{
+    switch (err) {
+    case INET_ERRNO_SYSTEM_LIMIT:
+	return "system_limit";
+    default:
+	return erl_errno_id(err);
+    }
+}
+
 /* general control reply function */
 static ErlDrvSSizeT ctl_reply(int rep, char* buf, ErlDrvSizeT len,
 			      char** rbuf, ErlDrvSizeT rsize)
@@ -1665,13 +1682,9 @@ static ErlDrvSSizeT ctl_reply(int rep, char* buf, ErlDrvSizeT len,
 /* general control error reply function */
 static ErlDrvSSizeT ctl_error(int err, char** rbuf, ErlDrvSizeT rsize)
 {
-    char response[256];		/* Response buffer. */
-    char* s;
-    char* t;
+    char* s = errno_str(err);
 
-    for (s = erl_errno_id(err), t = response; *s; s++, t++)
-	*t = tolower(*s);
-    return ctl_reply(INET_REP_ERROR, response, t-response, rbuf, rsize);
+    return ctl_reply(INET_REP_ERROR, s, strlen(s), rbuf, rsize);
 }
 
 static ErlDrvSSizeT ctl_xerror(char* xerr, char** rbuf, ErlDrvSizeT rsize)
@@ -1683,14 +1696,7 @@ static ErlDrvSSizeT ctl_xerror(char* xerr, char** rbuf, ErlDrvSizeT rsize)
 
 static ErlDrvTermData error_atom(int err)
 {
-    char errstr[256];
-    char* s;
-    char* t;
-
-    for (s = erl_errno_id(err), t = errstr; *s; s++, t++)
-	*t = tolower(*s);
-    *t = '\0';
-    return driver_mk_atom(errstr);
+    return driver_mk_atom(errno_str(err));
 }
 
 
@@ -8050,7 +8056,7 @@ static ErlDrvData tcp_inet_start(ErlDrvPort port, char* args)
 
 /* Copy a descriptor, by creating a new port with same settings
  * as the descriptor desc.
- * return NULL on error (ENFILE no ports avail)
+ * return NULL on error (SYSTEM_LIMIT no ports avail)
  */
 static tcp_descriptor* tcp_inet_copy(tcp_descriptor* desc,SOCKET s,
 				     ErlDrvTermData owner, int* err)
@@ -8089,7 +8095,7 @@ static tcp_descriptor* tcp_inet_copy(tcp_descriptor* desc,SOCKET s,
     /* The new port will be linked and connected to the original caller */
     port = driver_create_port(port, owner, "tcp_inet", (ErlDrvData) copy_desc);
     if ((long)port == -1) {
-	*err = ENFILE;
+	*err = INET_ERRNO_SYSTEM_LIMIT;
 	FREE(copy_desc);
 	return NULL;
     }
diff --git a/lib/kernel/doc/src/gen_tcp.xml b/lib/kernel/doc/src/gen_tcp.xml
index 8a5d40bb16..9f362841ce 100644
--- a/lib/kernel/doc/src/gen_tcp.xml
+++ b/lib/kernel/doc/src/gen_tcp.xml
@@ -235,7 +235,9 @@ do_recv(Sock, Bs) ->
         <p>Returns <c>{ok, <anno>Socket</anno>}</c> if a connection is established,
           or <c>{error, closed}</c> if <c><anno>ListenSocket</anno></c> is closed,
           or <c>{error, timeout}</c> if no connection is established
-          within the specified time. May also return a POSIX error
+          within the specified time,
+          or <c>{error, system_limit}</c> if all available ports in the
+          Erlang emulator are in use. May also return a POSIX error
           value if something else goes wrong, see inet(3) for possible
           error values.</p>
         <p>Packets can be sent to the returned socket <c><anno>Socket</anno></c>
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index 1a05b4ba99..86950b3ecc 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -149,7 +149,7 @@ fe80::204:acff:fe17:bf38
       <fsummary>Return a descriptive string for an error reason</fsummary>
       <desc>
         <p>Returns a diagnostic error string. See the section below
-          for possible <c><anno>Posix</anno></c> values and the corresponding
+          for possible Posix values and the corresponding
           strings.</p>
       </desc>
     </func>
diff --git a/lib/kernel/src/gen_tcp.erl b/lib/kernel/src/gen_tcp.erl
index 4d6c7f5f1d..02a6190034 100644
--- a/lib/kernel/src/gen_tcp.erl
+++ b/lib/kernel/src/gen_tcp.erl
@@ -194,7 +194,7 @@ listen(Port, Opts) ->
 -spec accept(ListenSocket) -> {ok, Socket} | {error, Reason} when
       ListenSocket :: socket(),
       Socket :: socket(),
-      Reason :: closed | timeout | inet:posix().
+      Reason :: closed | timeout | system_limit | inet:posix().
 
 accept(S) ->
     case inet_db:lookup_socket(S) of
diff --git a/lib/kernel/src/inet.erl b/lib/kernel/src/inet.erl
index 49f64a9236..4de3c1c6b1 100644
--- a/lib/kernel/src/inet.erl
+++ b/lib/kernel/src/inet.erl
@@ -1218,11 +1218,13 @@ port_list(Name) ->
 %%  utils
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
--spec format_error(Posix) -> string() when
-      Posix :: posix().
+-spec format_error(Reason) -> string() when
+      Reason :: posix() | system_limit.
 
 format_error(exbadport) -> "invalid port state";
 format_error(exbadseq) ->  "bad command sequence";
+format_error(system_limit) ->
+    "a system limit was hit, probably not enough ports";
 format_error(Tag) ->
     erl_posix_msg:message(Tag).
 
diff --git a/lib/kernel/test/gen_tcp_misc_SUITE.erl b/lib/kernel/test/gen_tcp_misc_SUITE.erl
index 3da4b07c05..d9bba0dbb0 100644
--- a/lib/kernel/test/gen_tcp_misc_SUITE.erl
+++ b/lib/kernel/test/gen_tcp_misc_SUITE.erl
@@ -39,7 +39,8 @@
 	 accept_timeouts_in_order/1,accept_timeouts_in_order2/1,
 	 accept_timeouts_in_order3/1,accept_timeouts_mixed/1, 
 	 killing_acceptor/1,killing_multi_acceptors/1,killing_multi_acceptors2/1,
-	 several_accepts_in_one_go/1,active_once_closed/1, send_timeout/1, send_timeout_active/1, 
+	 several_accepts_in_one_go/1, accept_system_limit/1,
+	 active_once_closed/1, send_timeout/1, send_timeout_active/1,
 	 otp_7731/1, zombie_sockets/1, otp_7816/1, otp_8102/1,
          otp_9389/1]).
 
@@ -71,7 +72,7 @@ all() ->
      accept_timeouts_in_order, accept_timeouts_in_order2,
      accept_timeouts_in_order3, accept_timeouts_mixed,
      killing_acceptor, killing_multi_acceptors,
-     killing_multi_acceptors2, several_accepts_in_one_go,
+     killing_multi_acceptors2, several_accepts_in_one_go, accept_system_limit,
      active_once_closed, send_timeout, send_timeout_active, otp_7731,
      zombie_sockets, otp_7816, otp_8102, otp_9389].
 
@@ -1837,6 +1838,54 @@ wait_until_accepting(Proc,N) ->
     end.
 
 
+accept_system_limit(suite) ->
+    [];
+accept_system_limit(doc) ->
+    ["Check that accept returns {error, system_limit} "
+     "(and not {error, enfile}) when running out of ports"];
+accept_system_limit(Config) when is_list(Config) ->
+    ?line {ok, LS} = gen_tcp:listen(0, []),
+    ?line {ok, TcpPort} = inet:port(LS),
+    ?line Connector = spawn_link(fun () -> connector(TcpPort) end),
+    ?line ok = acceptor(LS, false, []),
+    ?line Connector ! stop,
+    ok.
+
+acceptor(LS, GotSL, A) ->
+    case gen_tcp:accept(LS, 1000) of
+	{ok, S} ->
+	    acceptor(LS, GotSL, [S|A]);
+	{error, system_limit} ->
+	    acceptor(LS, true, A);
+	{error, timeout} when GotSL ->
+	    ok;
+	{error, timeout} ->
+	    error
+    end.
+
+connector(TcpPort) ->
+    ManyPorts = open_ports([]),
+    ConnF = fun (Port) ->
+		    case catch gen_tcp:connect({127,0,0,1}, TcpPort, []) of
+			{ok, Sock} ->
+			    Sock;
+			_Error ->
+			    port_close(Port)
+		    end
+	    end,
+    R = [ConnF(Port) || Port <- lists:sublist(ManyPorts, 10)],
+    receive stop -> R end.
+
+open_ports(L) ->
+    case catch open_port({spawn_driver, "ram_file_drv"}, []) of
+	Port when is_port(Port) ->
+	    open_ports([Port|L]);
+	{'EXIT', {system_limit, _}} ->
+	    {L1, L2} = lists:split(5, L),
+	    [port_close(Port) || Port <- L1],
+	    L2
+    end.
+
 
 active_once_closed(suite) ->
     [];