Merge branch 'raimo/linux-network-namespace-sockopt/OTP-11157' into maint

* raimo/linux-network-namespace-sockopt/OTP-11157:
  Document socket option 'netns'
  Rudimentary test
  Make netns option value a string
  Implement netns for SCTP + bugfixes
  Implement netns option for TCP and UDP
  Implement emulator netns support for TCP and UDP

8 files changed, 439 insertions, 27 deletions

diff --git a/erts/configure.in b/erts/configure.in
index 64436e933c..00c7045ea2 100644
--- a/erts/configure.in
+++ b/erts/configure.in
@@ -1679,6 +1679,10 @@ if test x"$ac_cv_header_netinet_sctp_h" = x"yes"; then
         ])
 fi
 
+dnl Check for setns
+AC_CHECK_HEADERS(sched.h setns.h)
+AC_CHECK_FUNCS([setns])
+
 HAVE_VALGRIND=no
 AC_CHECK_HEADER(valgrind/valgrind.h, HAVE_VALGRIND=yes)
 AC_SUBST(HAVE_VALGRIND)
diff --git a/erts/emulator/drivers/common/inet_drv.c b/erts/emulator/drivers/common/inet_drv.c
index 301ce2d0e2..60db50e80a 100644
--- a/erts/emulator/drivers/common/inet_drv.c
+++ b/erts/emulator/drivers/common/inet_drv.c
@@ -282,7 +282,7 @@ static BOOL (WINAPI *fpSetHandleInformation)(HANDLE,DWORD,DWORD);
 static unsigned long zero_value = 0;
 static unsigned long one_value = 1;
 
-#else
+#else /* #ifdef __WIN32__ */
 
 #include <sys/time.h>
 #ifdef NETDB_H_NEEDS_IN_H
@@ -315,9 +315,17 @@ static unsigned long one_value = 1;
 
 #include <net/if.h>
 
+#ifdef HAVE_SCHED_H
+#include <sched.h>
+#endif
+
+#ifdef HAVE_SETNS_H
+#include <setns.h>
+#endif
+
 /* SCTP support -- currently for UNIX platforms only: */
 #undef HAVE_SCTP
-#if (!defined(__WIN32__) && defined(HAVE_SCTP_H))
+#if defined(HAVE_SCTP_H)
 
 #include <netinet/sctp.h>
 
@@ -418,7 +426,7 @@ static int (*p_sctp_bindx)(int sd, struct sockaddr *addrs,
 static int (*p_sctp_peeloff)(int sd, sctp_assoc_t assoc_id) = NULL;
 #endif
 
-#endif /* SCTP supported */
+#endif /* #if defined(HAVE_SCTP_H) */
 
 #ifndef WANT_NONBLOCKING
 #define WANT_NONBLOCKING
@@ -512,7 +520,7 @@ static int my_strncasecmp(const char *s1, const char *s2, size_t n)
    } while(0)
 
 
-#endif /* __WIN32__ */
+#endif /* #ifdef __WIN32__    #else */
 
 #ifdef HAVE_SOCKLEN_T
 #  define SOCKLEN_T socklen_t
@@ -680,6 +688,7 @@ static int my_strncasecmp(const char *s1, const char *s2, size_t n)
 #define INET_LOPT_TCP_SEND_TIMEOUT_CLOSE 35  /* auto-close on send timeout or not */
 #define INET_LOPT_MSGQ_HIWTRMRK     36  /* set local msgq high watermark */
 #define INET_LOPT_MSGQ_LOWTRMRK     37  /* set local msgq low watermark */
+#define INET_LOPT_NETNS             38  /* Network namespace pathname */
 /* SCTP options: a separate range, from 100: */
 #define SCTP_OPT_RTOINFO		100
 #define SCTP_OPT_ASSOCINFO		101
@@ -955,6 +964,10 @@ typedef struct {
     int is_ignored;             /* if a fd is ignored by the inet_drv.
 				   This flag should be set to true when
 				   the fd is used outside of inet_drv. */
+#ifdef HAVE_SETNS
+    char *netns;                /* Socket network namespace name
+				   as full file path */
+#endif
 } inet_descriptor;
 
 
@@ -1181,6 +1194,7 @@ static ErlDrvTermData am_dontroute;
 static ErlDrvTermData am_priority;
 static ErlDrvTermData am_tos;
 static ErlDrvTermData am_ipv6_v6only;
+static ErlDrvTermData am_netns;
 #endif
 
 /* speical errors for bad ports and sequences */
@@ -3498,6 +3512,7 @@ static void inet_init_sctp(void) {
     INIT_ATOM(priority);
     INIT_ATOM(tos);
     INIT_ATOM(ipv6_v6only);
+    INIT_ATOM(netns);
     
     /* Option names */
     INIT_ATOM(sctp_rtoinfo);
@@ -3908,12 +3923,81 @@ static int erl_inet_close(inet_descriptor* desc)
 static ErlDrvSSizeT inet_ctl_open(inet_descriptor* desc, int domain, int type,
 				  char** rbuf, ErlDrvSizeT rsize)
 {
+    int save_errno;
+#ifdef HAVE_SETNS
+    int current_ns, new_ns;
+    current_ns = new_ns = 0;
+#endif
+    save_errno = 0;
+
     if (desc->state != INET_STATE_CLOSED)
 	return ctl_xerror(EXBADSEQ, rbuf, rsize);
+
+#ifdef HAVE_SETNS
+    if (desc->netns != NULL) {
+	/* Temporarily change network namespace for this thread
+	 * while creating the socket
+	 */
+	current_ns = open("/proc/self/ns/net", O_RDONLY);
+	if (current_ns == INVALID_SOCKET)
+	    return ctl_error(sock_errno(), rbuf, rsize);
+	new_ns = open(desc->netns, O_RDONLY);
+	if (new_ns == INVALID_SOCKET) {
+	    save_errno = sock_errno();
+	    while (close(current_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	    return ctl_error(save_errno, rbuf, rsize);
+	}
+	if (setns(new_ns, CLONE_NEWNET) != 0) {
+	    save_errno = sock_errno();
+	    while (close(new_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	    while (close(current_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	    return ctl_error(save_errno, rbuf, rsize);
+	}
+	else {
+	    while (close(new_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	}
+    }
+#endif
     if ((desc->s = sock_open(domain, type, desc->sprotocol)) == INVALID_SOCKET)
-	return ctl_error(sock_errno(), rbuf, rsize);
-    if ((desc->event = sock_create_event(desc)) == INVALID_EVENT)
-	return ctl_error(sock_errno(), rbuf, rsize);
+	save_errno = sock_errno();
+#ifdef HAVE_SETNS
+    if (desc->netns != NULL) {
+	/* Restore network namespace */
+	if (setns(current_ns, CLONE_NEWNET) != 0) {
+	    /* XXX Failed to restore network namespace.
+	     * What to do? Tidy up and return an error...
+	     * Note that the thread now might still be in the namespace.
+	     * Can this even happen? Should the emulator be aborted?
+	     */
+	    if (desc->s != INVALID_SOCKET)
+		save_errno = sock_errno();
+	    while (close(desc->s) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	    desc->s = INVALID_SOCKET;
+	    while (close(current_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	    return ctl_error(save_errno, rbuf, rsize);
+	}
+	else {
+	    while (close(current_ns) == INVALID_SOCKET &&
+		   sock_errno() == EINTR);
+	}
+    }
+#endif
+    if (desc->s == INVALID_SOCKET)
+	return ctl_error(save_errno, rbuf, rsize);
+
+    if ((desc->event = sock_create_event(desc)) == INVALID_EVENT) {
+	save_errno = sock_errno();
+	while (close(desc->s) == INVALID_SOCKET &&
+	       sock_errno() == EINTR);
+	desc->s = INVALID_SOCKET;
+	return ctl_error(save_errno, rbuf, rsize);
+    }
     SET_NONBLOCKING(desc->s);
 #ifdef __WIN32__
     driver_select(desc->port, desc->event, ERL_DRV_READ, 1);
@@ -5529,6 +5613,20 @@ static int inet_set_opts(inet_descriptor* desc, char* ptr, int len)
 	    }
 	    continue;
 
+#ifdef HAVE_SETNS
+	case INET_LOPT_NETNS:
+	    /* It is annoying that ival and len are both (signed) int */
+	    if (ival < 0) return -1;
+	    if (len < ival) return -1;
+	    if (desc->netns != NULL) FREE(desc->netns);
+	    desc->netns = ALLOC(((unsigned int) ival) + 1);
+	    memcpy(desc->netns, ptr, ival);
+	    desc->netns[ival] = '\0';
+	    ptr += ival;
+	    len -= ival;
+	    continue;
+#endif
+
 	case INET_OPT_REUSEADDR: 
 #ifdef __WIN32__
 	    continue;  /* Bjorn says */
@@ -5858,6 +5956,21 @@ static int sctp_set_opts(inet_descriptor* desc, char* ptr, int len)
 	    res = 0;
 	    continue;
 
+#ifdef HAVE_SETNS
+	case INET_LOPT_NETNS:
+	{
+	    size_t ns_len;
+	    ns_len = get_int32(curr);                   curr += 4;
+	    CHKLEN(curr, ns_len);
+	    if (desc->netns != NULL) FREE(desc->netns);
+	    desc->netns = ALLOC(ns_len + 1);
+	    memcpy(desc->netns, curr, ns_len);
+	    desc->netns[ns_len] = '\0';
+	    curr += ns_len;
+	}
+	    continue;
+#endif
+
 	/* SCTP options and applicable generic INET options: */
 
 	case SCTP_OPT_RTOINFO:
@@ -6454,6 +6567,22 @@ static ErlDrvSSizeT inet_fill_opts(inet_descriptor* desc,
 	    }
 	    continue;
 
+#ifdef HAVE_SETNS
+	case INET_LOPT_NETNS:
+	    if (desc->netns != NULL) {
+		size_t netns_len;
+		netns_len = strlen(desc->netns);
+		*ptr++ = opt;
+		put_int32(netns_len, ptr);
+		PLACE_FOR(netns_len, ptr);
+		memcpy(ptr, desc->netns, netns_len);
+		ptr += netns_len;
+	    } else {
+		TRUNCATE_TO(0,ptr);
+	    }
+	    continue;
+#endif
+
 	case INET_OPT_PRIORITY:
 #ifdef SO_PRIORITY
 	    type = SO_PRIORITY;
@@ -6737,6 +6866,22 @@ static ErlDrvSSizeT sctp_fill_opts(inet_descriptor* desc,
 	    break;
 	}
 
+#ifdef HAVE_SETNS
+	case INET_LOPT_NETNS:
+	    if (desc->netns != NULL) {
+		PLACE_FOR
+		    (spec, i,
+		     LOAD_ATOM_CNT + LOAD_BUF2BINARY_CNT + LOAD_TUPLE_CNT);
+		i = LOAD_ATOM (spec, i, am_netns);
+		i = LOAD_BUF2BINARY
+		    (spec, i, desc->netns, strlen(desc->netns));
+		i = LOAD_TUPLE (spec, i, 2);
+		break;
+	    }
+	    else
+		continue; /* Ignore */
+#endif
+
 	/* SCTP and generic INET options: */
 
 	case SCTP_OPT_RTOINFO:
@@ -7458,6 +7603,10 @@ static ErlDrvSSizeT inet_subscribe(inet_descriptor* desc,
 static void inet_stop(inet_descriptor* desc)
 {
     erl_inet_close(desc);
+#ifdef HAVE_SETNS
+    if (desc->netns != NULL)
+	FREE(desc->netns);
+#endif
     FREE(desc);
 }
 
@@ -7537,6 +7686,10 @@ static ErlDrvData inet_start(ErlDrvPort port, int size, int protocol)
 
     desc->is_ignored = 0;
 
+#ifdef HAVE_SETNS
+    desc->netns = NULL;
+#endif
+
     return (ErlDrvData)desc;
 }
 
diff --git a/erts/preloaded/ebin/prim_inet.beam b/erts/preloaded/ebin/prim_inet.beam
index 8638ef677e..5b38871282 100644
--- a/erts/preloaded/ebin/prim_inet.beam
+++ b/erts/preloaded/ebin/prim_inet.beam
diff --git a/erts/preloaded/src/prim_inet.erl b/erts/preloaded/src/prim_inet.erl
index fb1269cf91..fa621681f3 100644
--- a/erts/preloaded/src/prim_inet.erl
+++ b/erts/preloaded/src/prim_inet.erl
@@ -25,7 +25,7 @@
 
 %% Primitive inet_drv interface
 
--export([open/3, fdopen/4, close/1]).
+-export([open/3, open/4, fdopen/4, close/1]).
 -export([bind/3, listen/1, listen/2, peeloff/2]).
 -export([connect/3, connect/4, async_connect/4]).
 -export([accept/1, accept/2, async_accept/2]).
@@ -64,22 +64,31 @@
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 open(Protocol, Family, Type) ->
-    open(Protocol, Family, Type, ?INET_REQ_OPEN, []).
+    open(Protocol, Family, Type, [], ?INET_REQ_OPEN, []).
+
+open(Protocol, Family, Type, Opts) ->
+    open(Protocol, Family, Type, Opts, ?INET_REQ_OPEN, []).
 
 fdopen(Protocol, Family, Type, Fd) when is_integer(Fd) ->
-    open(Protocol, Family, Type, ?INET_REQ_FDOPEN, ?int32(Fd)).
+    open(Protocol, Family, Type, [], ?INET_REQ_FDOPEN, ?int32(Fd)).
 
-open(Protocol, Family, Type, Req, Data) ->
+open(Protocol, Family, Type, Opts, Req, Data) ->
     Drv = protocol2drv(Protocol),
     AF = enc_family(Family),
     T = enc_type(Type),
     try erlang:open_port({spawn_driver,Drv}, [binary]) of
 	S ->
-	    case ctl_cmd(S, Req, [AF,T,Data]) of
-		{ok,_} -> {ok,S};
-		{error,_}=Error ->
+	    case setopts(S, Opts) of
+		ok ->
+		    case ctl_cmd(S, Req, [AF,T,Data]) of
+			{ok,_} -> {ok,S};
+			{error,_}=E1 ->
+			    close(S),
+			    E1
+		    end;
+		{error,_}=E2 ->
 		    close(S),
-		    Error
+		    E2
 	    end
     catch
 	%% The only (?) way to get here is to try to open
@@ -1108,6 +1117,7 @@ enc_opt(send_timeout_close) -> ?INET_LOPT_TCP_SEND_TIMEOUT_CLOSE;
 enc_opt(delay_send)      -> ?INET_LOPT_TCP_DELAY_SEND;
 enc_opt(packet_size)     -> ?INET_LOPT_PACKET_SIZE;
 enc_opt(read_packets)    -> ?INET_LOPT_READ_PACKETS;
+enc_opt(netns)           -> ?INET_LOPT_NETNS;
 enc_opt(raw)             -> ?INET_OPT_RAW;
 % Names of SCTP opts:
 enc_opt(sctp_rtoinfo)	 	   -> ?SCTP_OPT_RTOINFO;
@@ -1164,6 +1174,7 @@ dec_opt(?INET_LOPT_TCP_SEND_TIMEOUT_CLOSE) -> send_timeout_close;
 dec_opt(?INET_LOPT_TCP_DELAY_SEND)   -> delay_send;
 dec_opt(?INET_LOPT_PACKET_SIZE)      -> packet_size;
 dec_opt(?INET_LOPT_READ_PACKETS)     -> read_packets;
+dec_opt(?INET_LOPT_NETNS)           -> netns;
 dec_opt(?INET_OPT_RAW)              -> raw;
 dec_opt(I) when is_integer(I)     -> undefined.
 
@@ -1261,6 +1272,7 @@ type_opt_1(send_timeout_close) -> bool;
 type_opt_1(delay_send)      -> bool;
 type_opt_1(packet_size)     -> uint;
 type_opt_1(read_packets)    -> uint;
+type_opt_1(netns)           -> binary;
 %% 
 %% SCTP options (to be set). If the type is a record type, the corresponding
 %% record signature is returned, otherwise, an "elementary" type tag 
@@ -1487,9 +1499,12 @@ type_value_2({bitenumlist,List,_}, EnumList) ->
 	Ls when is_list(Ls)                         -> true;
 	false                                       -> false
     end;
-type_value_2(binary,Bin) when is_binary(Bin) -> true;
-type_value_2(binary_or_uint,Bin) when is_binary(Bin) -> true;
-type_value_2(binary_or_uint,Int) when is_integer(Int), Int >= 0 -> true;
+type_value_2(binary,Bin)
+  when is_binary(Bin), byte_size(Bin) < (1 bsl 32)  -> true;
+type_value_2(binary_or_uint,Bin)
+  when is_binary(Bin), byte_size(Bin) < (1 bsl 32)  -> true;
+type_value_2(binary_or_uint,Int)
+  when is_integer(Int), Int >= 0                    -> true;
 %% Type-checking of SCTP options
 type_value_2(sctp_assoc_id, X)
   when X band 16#ffffffff =:= X                     -> true;
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index 254dfbf034..fd62f778a2 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -722,6 +722,59 @@ fe80::204:acff:fe17:bf38
 			  <p>Received <c>Packet</c> is delivered as defined by Mode.</p>
 		  </item>
 
+	  <tag><c>{netns, Namespace :: file:filename_all()}</c></tag>
+	  <item>
+	    <p>Set a network namespace for the socket. The <c>Namespace</c>
+	    parameter is a filename defining the namespace for example
+	    <c>"/var/run/netns/example"</c> typically created by the command
+	    <c>ip netns add example</c>. This option must be used in a
+	    function call that creates a socket i.e
+	    <seealso marker="gen_tcp#connect/3">
+	      gen_tcp:connect/3,4</seealso>,
+	    <seealso marker="gen_tcp#listen/2">
+	      gen_tcp:listen/2</seealso>,
+	    <seealso marker="gen_udp#open/1">
+	      gen_udp:open/1,2</seealso> or
+	    <seealso marker="gen_sctp#open/0">
+	      gen_sctp:open/0-2</seealso>.
+	    </p>
+	    <p>This option uses the Linux specific syscall
+	    <c>setns()</c> such as in Linux kernel 3.0 or later
+	    and therefore only exists when the runtime system
+	    has been compiled for such an operating system.
+	    </p>
+	    <p>
+	    The virtual machine also needs elevated privileges either
+	    running as superuser or (for Linux) having the capability
+	    <c>CAP_SYS_ADMIN</c> according to the documentation for setns(2).
+	    However, during testing also <c>CAP_SYS_PTRACE</c>
+	    and <c>CAP_DAC_READ_SEARCH</c> has proven to be necessary.
+	    Example:<code>
+setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp
+</code>
+            Note also that the filesystem containing the virtual machine
+	    executable (<c>beam.smp</c> in the example above) has to be local,
+	    mounted without the <c>nosetuid</c> flag,
+	    support extended attributes and that
+	    the kernel has to support file capabilities.
+	    All this runs out of the box on at least Ubuntu 12.04 LTS,
+	    except that SCTP sockets appears to not support
+	    network namespaces.
+	    </p>
+	    <p>The <c>Namespace</c> is a file name and is encoded
+	    and decoded as discussed in
+	    <seealso marker="file">file</seealso>
+	    except that the emulator flag <c>+fnu</c> is ignored and
+	    <seealso marker="#getopts/2">getopts/2</seealso>
+	    for this option will return a binary for the filename
+	    if the stored filename can not be decoded,
+	    which should only happen if you set the option using a binary
+	    that can not be decoded with the emulator's filename encoding:
+	    <seealso marker="file#native_name_encoding/0">
+	      file:native_name_encoding/0</seealso>.
+	    </p>
+	  </item>
+
 		  <tag><c>list</c></tag>
           <item>
 			  <p>Received <c>Packet</c> is delivered as a list.</p>
diff --git a/lib/kernel/src/inet.erl b/lib/kernel/src/inet.erl
index 5749027acd..27f085c3aa 100644
--- a/lib/kernel/src/inet.erl
+++ b/lib/kernel/src/inet.erl
@@ -200,7 +200,14 @@ send(Socket, Packet) ->
       Options :: [socket_setopt()].
 
 setopts(Socket, Opts) -> 
-    prim_inet:setopts(Socket, Opts).
+    SocketOpts =
+	[case Opt of
+	     {netns,NS} ->
+		 {netns,filename2binary(NS)};
+	     _ ->
+		 Opt
+	 end || Opt <- Opts],
+    prim_inet:setopts(Socket, SocketOpts).
 
 -spec getopts(Socket, Options) ->
 	{'ok', OptionValues} | {'error', posix()} when
@@ -209,7 +216,18 @@ setopts(Socket, Opts) ->
       OptionValues :: [socket_setopt()].
 
 getopts(Socket, Opts) ->
-    prim_inet:getopts(Socket, Opts).
+    case prim_inet:getopts(Socket, Opts) of
+	{ok,OptionValues} ->
+	    {ok,
+	     [case OptionValue of
+		  {netns,Bin} ->
+		      {netns,binary2filename(Bin)};
+		  _ ->
+		      OptionValue
+	      end || OptionValue <- OptionValues]};
+	Other ->
+	    Other
+    end.
 
 -spec getifaddrs(Socket :: socket()) ->
 	{'ok', [string()]} | {'error', posix()}.
@@ -641,6 +659,14 @@ con_opt([Opt | Opts], R, As) ->
 	{tcp_module,_}  -> con_opt(Opts, R, As);
 	inet        -> con_opt(Opts, R, As);
 	inet6       -> con_opt(Opts, R, As);
+	{netns,NS} ->
+	    BinNS = filename2binary(NS),
+	    case prim_inet:is_sockopt_val(netns, BinNS) of
+		true ->
+		    con_opt(Opts, R#connect_opts { fd = [{netns,BinNS}] }, As);
+		false ->
+		    {error, badarg}
+	    end;
 	{Name,Val} when is_atom(Name) -> con_add(Name, Val, R, Opts, As);
 	_ -> {error, badarg}
     end;
@@ -699,6 +725,14 @@ list_opt([Opt | Opts], R, As) ->
 	{tcp_module,_}  -> list_opt(Opts, R, As);
 	inet         -> list_opt(Opts, R, As);
 	inet6        -> list_opt(Opts, R, As);
+	{netns,NS} ->
+	    BinNS = filename2binary(NS),
+	    case prim_inet:is_sockopt_val(netns, BinNS) of
+		true ->
+		    list_opt(Opts, R#listen_opts { fd = [{netns,BinNS}] }, As);
+		false ->
+		    {error, badarg}
+	    end;
 	{Name,Val} when is_atom(Name) -> list_add(Name, Val, R, Opts, As);
 	_ -> {error, badarg}
     end;
@@ -745,6 +779,14 @@ udp_opt([Opt | Opts], R, As) ->
 	{udp_module,_} -> udp_opt(Opts, R, As);
 	inet        -> udp_opt(Opts, R, As);
 	inet6       -> udp_opt(Opts, R, As);
+	{netns,NS} ->
+	    BinNS = filename2binary(NS),
+	    case prim_inet:is_sockopt_val(netns, BinNS) of
+		true ->
+		    list_opt(Opts, R#udp_opts { fd = [{netns,BinNS}] }, As);
+		false ->
+		    {error, badarg}
+	    end;
 	{Name,Val} when is_atom(Name) -> udp_add(Name, Val, R, Opts, As);
 	_ -> {error, badarg}
     end;
@@ -814,6 +856,17 @@ sctp_opt([Opt|Opts], Mod, R, As) ->
 	{sctp_module,_}	-> sctp_opt (Opts, Mod, R, As); % Done with
 	inet		-> sctp_opt (Opts, Mod, R, As); % Done with
 	inet6		-> sctp_opt (Opts, Mod, R, As); % Done with
+	{netns,NS} ->
+	    BinNS = filename2binary(NS),
+	    case prim_inet:is_sockopt_val(netns, BinNS) of
+		true ->
+		    sctp_opt(
+		      Opts, Mod,
+		      R#sctp_opts { fd = [{netns,BinNS}] },
+		      As);
+		false ->
+		    {error, badarg}
+	    end;
 	{Name,Val}	-> sctp_opt (Opts, Mod, R, As, Name, Val);
 	_ -> {error,badarg}
     end;
@@ -858,6 +911,39 @@ add_opt(Name, Val, Opts, As) ->
     end.
 	
 
+%% Passthrough all unknown - catch type errors later
+filename2binary(List) when is_list(List) ->
+    OutEncoding = file:native_name_encoding(),
+    try unicode:characters_to_binary(List, unicode, OutEncoding) of
+	Bin when is_binary(Bin) ->
+	    Bin;
+	_ ->
+	    List
+    catch
+	error:badarg ->
+	    List
+    end;
+filename2binary(Bin) ->
+    Bin.
+
+binary2filename(Bin) ->
+    InEncoding = file:native_name_encoding(),
+    case unicode:characters_to_list(Bin, InEncoding) of
+	Filename when is_list(Filename) ->
+	    Filename;
+	_ ->
+	    %% For getopt/setopt of netns this should only happen if
+	    %% a binary with wrong encoding was used when setting the
+	    %% option, hence the user shall eat his/her own medicine.
+	    %%
+	    %% I.e passthrough here too for now.
+	    %% Future usecases will most probably not want this,
+	    %% rather Unicode error or warning
+	    %% depending on emulator flag instead.
+	    Bin
+    end.
+
+
 translate_ip(any,      inet) -> {0,0,0,0};
 translate_ip(loopback, inet) -> {127,0,0,1};
 translate_ip(any,      inet6) -> {0,0,0,0,0,0,0,0};
@@ -1070,7 +1156,7 @@ gethostbyaddr_tm_native(Addr, Timer, Opts) ->
 	Result -> Result
     end.
 
--spec open(Fd :: integer(),
+-spec open(Fd_or_OpenOpts :: integer() | list(),
 	   Addr :: ip_address(),
 	   Port :: port_number(),
 	   Opts :: [socket_setopt()],
@@ -1080,8 +1166,14 @@ gethostbyaddr_tm_native(Addr, Timer, Opts) ->
 	   Module :: atom()) ->
 	{'ok', socket()} | {'error', posix()}.
 
-open(Fd, Addr, Port, Opts, Protocol, Family, Type, Module) when Fd < 0 ->
-    case prim_inet:open(Protocol, Family, Type) of
+open(FdO, Addr, Port, Opts, Protocol, Family, Type, Module)
+  when is_integer(FdO), FdO < 0;
+       is_list(FdO) ->
+    OpenOpts =
+	if  is_list(FdO) -> FdO;
+	    true -> []
+	end,
+    case prim_inet:open(Protocol, Family, Type, OpenOpts) of
 	{ok,S} ->
 	    case prim_inet:setopts(S, Opts) of
 		ok ->
@@ -1104,7 +1196,8 @@ open(Fd, Addr, Port, Opts, Protocol, Family, Type, Module) when Fd < 0 ->
 	Error ->
 	    Error
     end;
-open(Fd, _Addr, _Port, Opts, Protocol, Family, Type, Module) ->
+open(Fd, _Addr, _Port, Opts, Protocol, Family, Type, Module)
+  when is_integer(Fd) ->
     fdopen(Fd, Opts, Protocol, Family, Type, Module).
 
 bindx(S, [Addr], Port0) ->
diff --git a/lib/kernel/src/inet_int.hrl b/lib/kernel/src/inet_int.hrl
index 67a99913a1..18a4a61b2f 100644
--- a/lib/kernel/src/inet_int.hrl
+++ b/lib/kernel/src/inet_int.hrl
@@ -143,6 +143,7 @@
 -define(INET_LOPT_TCP_SEND_TIMEOUT_CLOSE, 35).
 -define(INET_LOPT_MSGQ_HIWTRMRK,  36).
 -define(INET_LOPT_MSGQ_LOWTRMRK,  37).
+-define(INET_LOPT_NETNS,          38).
 % Specific SCTP options: separate range:
 -define(SCTP_OPT_RTOINFO,	 	100).
 -define(SCTP_OPT_ASSOCINFO,	 	101).
diff --git a/lib/kernel/test/inet_SUITE.erl b/lib/kernel/test/inet_SUITE.erl
index 46c8c0b88b..ed43749cc0 100644
--- a/lib/kernel/test/inet_SUITE.erl
+++ b/lib/kernel/test/inet_SUITE.erl
@@ -38,10 +38,10 @@
 	 gethostnative_debug_level/0, gethostnative_debug_level/1,
 	 getif/1,
 	 getif_ifr_name_overflow/1,getservbyname_overflow/1, getifaddrs/1,
-	 parse_strict_address/1]).
+	 parse_strict_address/1, simple_netns/1]).
 
 -export([get_hosts/1, get_ipv6_hosts/1, parse_hosts/1, parse_address/1,
-	 kill_gethost/0, parallell_gethost/0]).
+	 kill_gethost/0, parallell_gethost/0, test_netns/0]).
 -export([init_per_testcase/2, end_per_testcase/2]).
 
 suite() -> [{ct_hooks,[ts_install_cth]}].
@@ -53,7 +53,7 @@ all() ->
      t_gethostnative, gethostnative_parallell, cname_loop,
      gethostnative_debug_level, gethostnative_soft_restart,
      getif, getif_ifr_name_overflow, getservbyname_overflow,
-     getifaddrs, parse_strict_address].
+     getifaddrs, parse_strict_address, simple_netns].
 
 groups() -> 
     [{parse, [], [parse_hosts, parse_address]}].
@@ -1099,3 +1099,96 @@ toupper([C|Cs]) when is_integer(C) ->
     end;
 toupper([]) ->
     [].
+
+
+simple_netns(Config) when is_list(Config) ->
+    {ok,U} = gen_udp:open(0),
+    case inet:setopts(U, [{netns,""}]) of
+	ok ->
+	    jog_netns_opt(U),
+	    ok = gen_udp:close(U),
+	    %%
+	    {ok,L} = gen_tcp:listen(0, []),
+	    jog_netns_opt(L),
+	    ok = gen_tcp:close(L),
+	    %%
+	    {ok,S} = gen_sctp:open(),
+	    jog_netns_opt(S),
+	    ok = gen_sctp:close(S);
+	{error,einval} ->
+	    {skip,"setns() not supported"}
+    end.
+
+jog_netns_opt(S) ->
+    %% This is just jogging the option mechanics
+    ok = inet:setopts(S, [{netns,""}]),
+    {ok,[{netns,""}]} = inet:getopts(S, [netns]),
+    ok = inet:setopts(S, [{netns,"/proc/self/ns/net"}]),
+    {ok,[{netns,"/proc/self/ns/net"}]} = inet:getopts(S, [netns]),
+    ok.
+
+
+%% Manual test to be run outside test_server in an emulator
+%% started by root, in a machine with setns() support...
+test_netns() ->
+    DefaultIF = v1,
+    DefaultIP = {192,168,1,17},
+    Namespace = "test",
+    NamespaceIF = v2,
+    NamespaceIP = {192,168,1,18},
+    %%
+    DefaultIPString = inet_parse:ntoa(DefaultIP),
+    NamespaceIPString = inet_parse:ntoa(NamespaceIP),
+    cmd("ip netns add ~s",
+	[Namespace]),
+    cmd("ip link add name ~w type veth peer name ~w netns ~s",
+        [DefaultIF,NamespaceIF,Namespace]),
+    cmd("ip netns exec ~s ip addr add ~s/30 dev ~w",
+	[Namespace,NamespaceIPString,NamespaceIF]),
+    cmd("ip netns exec ~s ip link set ~w up",
+	[Namespace,NamespaceIF]),
+    cmd("ip addr add ~s/30 dev ~w",
+	[DefaultIPString,DefaultIF]),
+    cmd("ip link set ~w up",
+	[DefaultIF]),
+    try test_netns(
+	  {DefaultIF,DefaultIP},
+	  filename:join("/var/run/netns/", Namespace),
+	  {NamespaceIF,NamespaceIP}) of
+	Result ->
+	    io:put_chars(["#### Test done",io_lib:nl()]),
+	    Result
+    after
+	cmd("ip link delete ~w type veth",
+	    [DefaultIF]),
+	cmd("ip netns delete ~s",
+	    [Namespace])
+    end.
+
+test_netns({DefaultIF,DefaultIP}, Namespace, {NamespaceIF,NamespaceIP}) ->
+    {ok,ListenSocket} = gen_tcp:listen(0, [{active,false}]),
+    {ok,[{addr,DefaultIP}]} = inet:ifget(ListenSocket, DefaultIF, [addr]),
+    {ok,ListenPort} = inet:port(ListenSocket),
+    {ok,ConnectSocket} =
+	gen_tcp:connect(
+	  DefaultIP, ListenPort, [{active,false},{netns,Namespace}], 3000),
+    {ok,[{addr,NamespaceIP}]} = inet:ifget(ConnectSocket, NamespaceIF, [addr]),
+    {ok,ConnectPort} = inet:port(ConnectSocket),
+    {ok,AcceptSocket} = gen_tcp:accept(ListenSocket, 0),
+    {ok,AcceptPort} = inet:port(AcceptSocket),
+    {ok,{NamespaceIP,ConnectPort}} = inet:peername(AcceptSocket),
+    {ok,{DefaultIP,AcceptPort}} = inet:peername(ConnectSocket),
+    ok = gen_tcp:send(ConnectSocket, "data"),
+    ok = gen_tcp:close(ConnectSocket),
+    {ok,"data"} = gen_tcp:recv(AcceptSocket, 4, 1000),
+    {error,closed} = gen_tcp:recv(AcceptSocket, 1, 1000),
+    ok = gen_tcp:close(AcceptSocket),
+    ok = gen_tcp:close(ListenSocket).
+
+cmd(Cmd, Args) ->
+    cmd(io_lib:format(Cmd, Args)).
+%%
+cmd(CmdString) ->
+    io:put_chars(["# ",CmdString,io_lib:nl()]),
+    io:put_chars([os:cmd(CmdString++" ; echo '  =>' $?")]),
+    ok.