Assign externally open fd to gen_tcp (UDS support)

When a AF_LOCAL file descriptor is created externally (e.g. Unix
Domain Socket) and passed to `gen_tcp:listen(0, [{fd, FD}])`, the
implementation incorrectly assigned the address family to be equal
to `inet`, which in the inet_drv driver translated to AF_INET instead
of AF_LOCAL (or AF_UNIX), and an `einval` error code was returned.
This patch fixes this problem such that the file descriptors of the
`local` address family are supported in the inet:fdopen/5,
gen_tcp:connect/3, gen_tcp:listen/2, gen_udp:open/2 calls

6 files changed, 48 insertions, 11 deletions

diff --git a/lib/kernel/doc/src/gen_tcp.xml b/lib/kernel/doc/src/gen_tcp.xml
index 6a19e76c4f..20a13782ca 100644
--- a/lib/kernel/doc/src/gen_tcp.xml
+++ b/lib/kernel/doc/src/gen_tcp.xml
@@ -132,6 +132,13 @@ do_recv(Sock, Bs) ->
             <p>Set up the socket for IPv6.</p>
           </item>
 
+		  <tag><c>local</c></tag>
+		  <item>
+            <p>Set up the socket for local address family. This option is only
+               valid together with <c>{fd, integer()}</c> when the file descriptor
+               is of local address family (e.g. a Unix Domain Socket)</p>
+          </item>
+
           <tag><c>{port, Port}</c></tag>
           <item>
             <p>Specify which local port number to use.</p>
diff --git a/lib/kernel/doc/src/gen_udp.xml b/lib/kernel/doc/src/gen_udp.xml
index 79cd87dcef..72f25d8d3f 100644
--- a/lib/kernel/doc/src/gen_udp.xml
+++ b/lib/kernel/doc/src/gen_udp.xml
@@ -101,6 +101,13 @@
             <p>Set up the socket for IPv4.</p>
           </item>
 
+		  <tag><c>local</c></tag>
+		  <item>
+            <p>Set up the socket for local address family. This option is only
+               valid together with <c>{fd, integer()}</c> when the file descriptor
+               is of local address family (e.g. a Unix Domain Socket)</p>
+          </item>
+
 		  <tag><c>{udp_module, module()}</c></tag>
 		  <item> <p>
 				  Override which callback module is used. Defaults to
diff --git a/lib/kernel/src/inet.erl b/lib/kernel/src/inet.erl
index b573112445..8840f05fa1 100644
--- a/lib/kernel/src/inet.erl
+++ b/lib/kernel/src/inet.erl
@@ -40,7 +40,7 @@
 
 -export([i/0, i/1, i/2]).
 
--export([getll/1, getfd/1, open/8, fdopen/6]).
+-export([getll/1, getfd/1, open/8, fdopen/6, getfamily/1]).
 
 -export([tcp_controlling_process/2, udp_controlling_process/2,
 	 tcp_close/1, udp_close/1]).
@@ -133,7 +133,7 @@
 		 'running' | 'multicast' | 'loopback']} |
       {'hwaddr', ether_address()}.
 
--type address_family() :: 'inet' | 'inet6'.
+-type address_family() :: 'inet' | 'inet6' | 'local'.
 -type socket_protocol() :: 'tcp' | 'udp' | 'sctp'.
 -type socket_type() :: 'stream' | 'dgram' | 'seqpacket'.
 -type stat_option() :: 
@@ -711,6 +711,7 @@ con_opt([Opt | Opts], #connect_opts{} = R, As) ->
 	{tcp_module,_}  -> con_opt(Opts, R, As);
 	inet        -> con_opt(Opts, R, As);
 	inet6       -> con_opt(Opts, R, As);
+	local       -> con_opt(Opts, R#connect_opts { family = local }, As);
 	{netns,NS} ->
 	    BinNS = filename2binary(NS),
 	    case prim_inet:is_sockopt_val(netns, BinNS) of
@@ -783,6 +784,7 @@ list_opt([Opt | Opts], #listen_opts{} = R, As) ->
 	{tcp_module,_}  -> list_opt(Opts, R, As);
 	inet         -> list_opt(Opts, R, As);
 	inet6        -> list_opt(Opts, R, As);
+	local        -> list_opt(Opts, R#listen_opts { family = local }, As);
 	{netns,NS} ->
 	    BinNS = filename2binary(NS),
 	    case prim_inet:is_sockopt_val(netns, BinNS) of
@@ -839,8 +841,9 @@ udp_opt([Opt | Opts], #udp_opts{} = R, As) ->
 	binary      ->  udp_add(mode, binary, R, Opts, As);
 	list        ->  udp_add(mode, list, R, Opts, As);
 	{udp_module,_} -> udp_opt(Opts, R, As);
-	inet        -> udp_opt(Opts, R, As);
-	inet6       -> udp_opt(Opts, R, As);
+	inet        ->  udp_opt(Opts, R, As);
+	inet6       ->  udp_opt(Opts, R, As);
+	local       ->  udp_opt(Opts, R#udp_opts { family = local }, As);
 	{netns,NS} ->
 	    BinNS = filename2binary(NS),
 	    case prim_inet:is_sockopt_val(netns, BinNS) of
@@ -1318,7 +1321,7 @@ fdopen(Fd, Addr, Port, Opts, Protocol, Family, Type, Module) ->
     Bound = Port == 0 andalso IsAnyAddr,
     case prim_inet:fdopen(Protocol, Family, Type, Fd, Bound) of
 	{ok, S} ->
-	    case prim_inet:setopts(S, Opts) of
+	    case prim_inet:setopts(S, Opts -- [local]) of
 		ok ->
                     case if
                              Bound ->
@@ -1345,6 +1348,13 @@ fdopen(Fd, Addr, Port, Opts, Protocol, Family, Type, Module) ->
 	Error -> Error
     end.
 
+-spec getfamily(list()) -> atom().
+getfamily(Options) when is_list(Options) ->
+    case lists:member(local, Options) of
+    true  -> local;
+    false -> inet
+    end.
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%  socket stat
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
diff --git a/lib/kernel/src/inet_int.hrl b/lib/kernel/src/inet_int.hrl
index e7c6cf8ae2..0a2201298a 100644
--- a/lib/kernel/src/inet_int.hrl
+++ b/lib/kernel/src/inet_int.hrl
@@ -29,6 +29,7 @@
 -define(INET_AF_INET6,        2).
 -define(INET_AF_ANY,          3). % Fake for ANY in any address family
 -define(INET_AF_LOOPBACK,     4). % Fake for LOOPBACK in any address family
+-define(INET_AF_LOCAL,        5). % For Unix Domain address family
 
 %% type codes to open and gettype - INET_REQ_GETTYPE
 -define(INET_TYPE_STREAM,     1).
@@ -378,7 +379,8 @@
 	{ 
 	  ifaddr = any,     %% bind to interface address
 	  port   = 0,       %% bind to port (default is dynamic port)
-	  fd      = -1,     %% fd >= 0 => already bound
+	  fd     = -1,      %% fd >= 0 => already bound
+	  family = inet,    %% address family
 	  opts   = []       %% [{active,true}] added in inet:connect_options
 	 }).
 
@@ -388,6 +390,7 @@
 	  port   = 0,                %% bind to port (default is dynamic port)
 	  backlog = ?LISTEN_BACKLOG, %% backlog
 	  fd      = -1,              %% %% fd >= 0 => already bound
+	  family = inet,             %% address family
 	  opts   = []                %% [{active,true}] added in 
 	                             %% inet:listen_options
 	 }).
@@ -397,6 +400,7 @@
 	  ifaddr = any,
 	  port   = 0,
 	  fd     = -1,
+	  family = inet,
 	  opts   = [{active,true}]
 	 }).
 
diff --git a/lib/kernel/src/inet_tcp.erl b/lib/kernel/src/inet_tcp.erl
index f551af9709..ad0a6159fe 100644
--- a/lib/kernel/src/inet_tcp.erl
+++ b/lib/kernel/src/inet_tcp.erl
@@ -108,9 +108,10 @@ do_connect({A,B,C,D}, Port, Opts, Time) when ?ip(A,B,C,D), ?port(Port) ->
 	{ok, #connect_opts{fd=Fd,
 			   ifaddr=BAddr={Ab,Bb,Cb,Db},
 			   port=BPort,
+			   family=Family,
 			   opts=SockOpts}}
 	when ?ip(Ab,Bb,Cb,Db), ?port(BPort) ->
-	    case inet:open(Fd,BAddr,BPort,SockOpts,tcp,inet,stream,?MODULE) of
+	    case inet:open(Fd,BAddr,BPort,SockOpts,tcp,Family,stream,?MODULE) of
 		{ok, S} ->
 		    case prim_inet:connect(S, {A,B,C,D}, Port, Time) of
 			ok    -> {ok,S};
@@ -130,9 +131,10 @@ listen(Port, Opts) ->
 	{ok, #listen_opts{fd=Fd,
 			  ifaddr=BAddr={A,B,C,D},
 			  port=BPort,
+			  family=Family,
 			  opts=SockOpts}=R}
 	when ?ip(A,B,C,D), ?port(BPort) ->
-	    case inet:open(Fd,BAddr,BPort,SockOpts,tcp,inet,stream,?MODULE) of
+	    case inet:open(Fd,BAddr,BPort,SockOpts,tcp,Family,stream,?MODULE) of
 		{ok, S} ->
 		    case prim_inet:listen(S, R#listen_opts.backlog) of
 			ok -> {ok, S};
@@ -165,4 +167,7 @@ accept(L,Timeout) ->
 %% Create a port/socket from a file descriptor 
 %%
 fdopen(Fd, Opts) ->
-    inet:fdopen(Fd, Opts, tcp, inet, stream, ?MODULE).
+    fdopen(Fd, inet:getfamily(Opts), Opts).
+
+fdopen(Fd, Family, Opts) ->
+    inet:fdopen(Fd, Opts, tcp, Family, stream, ?MODULE).
diff --git a/lib/kernel/src/inet_udp.erl b/lib/kernel/src/inet_udp.erl
index 5b2e5120c9..74b2874d5b 100644
--- a/lib/kernel/src/inet_udp.erl
+++ b/lib/kernel/src/inet_udp.erl
@@ -52,8 +52,9 @@ open(Port, Opts) ->
 	{ok, #udp_opts{fd=Fd,
 		       ifaddr=BAddr={A,B,C,D},
 		       port=BPort,
+		       family=Family,
 		       opts=SockOpts}} when ?ip(A,B,C,D), ?port(BPort) ->
-	    inet:open(Fd,BAddr,BPort,SockOpts,udp,inet,dgram,?MODULE);
+	    inet:open(Fd,BAddr,BPort,SockOpts,udp,Family,dgram,?MODULE);
 	{ok, _} -> exit(badarg)
     end.
 
@@ -92,9 +93,12 @@ controlling_process(Socket, NewOwner) ->
 %% Create a port/socket from a file descriptor 
 %%
 fdopen(Fd, Opts) ->
+    fdopen(Fd, inet:getfamily(Opts), Opts).
+
+fdopen(Fd, Family, Opts) ->
     inet:fdopen(Fd, 
 		optuniquify([{recbuf, ?RECBUF} | Opts]), 
-		udp, inet, dgram, ?MODULE).
+		udp, Family, dgram, ?MODULE).
 
 
 %% Remove all duplicate options from an option list.