ssh: Option max_channels added.

It actually counts the number of subsystem alive.  Allocating a channel does not consume any resources
(except some cpu cycles), but the subsystem start spawns processes.

4 files changed, 108 insertions, 7 deletions

diff --git a/lib/ssh/doc/src/ssh.xml b/lib/ssh/doc/src/ssh.xml
index cf5e8f1aff..37ed016099 100644
--- a/lib/ssh/doc/src/ssh.xml
+++ b/lib/ssh/doc/src/ssh.xml
@@ -501,6 +501,15 @@ kex is implicit but public_key is set explicitly.</p>
 	    </p>
 	  </item>
 
+	  <tag><c><![CDATA[{max_channels, pos_integer()}]]></c></tag>
+	  <item>
+	    <p>The maximum number of channels with active remote subsystem that are accepted for
+	    each connection to this daemon</p>
+	    <p>By default, this option is not set. This means that the number is not limited.
+	    </p>
+	  </item>
+
+
 	  <tag><c><![CDATA[{parallel_login, boolean()}]]></c></tag>
 	  <item>
 	    <p>If set to false (the default value), only one login is handled at a time.
diff --git a/lib/ssh/src/ssh.erl b/lib/ssh/src/ssh.erl
index 132de71aed..ee44324c12 100644
--- a/lib/ssh/src/ssh.erl
+++ b/lib/ssh/src/ssh.erl
@@ -385,6 +385,8 @@ handle_option([{rekey_limit, _} = Opt|Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{max_sessions, _} = Opt|Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
+handle_option([{max_channels, _} = Opt|Rest], SocketOptions, SshOptions) ->
+    handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{negotiation_timeout, _} = Opt|Rest], SocketOptions, SshOptions) ->
     handle_option(Rest, SocketOptions, [handle_ssh_option(Opt) | SshOptions]);
 handle_option([{parallel_login, _} = Opt|Rest], SocketOptions, SshOptions) ->
@@ -443,6 +445,8 @@ handle_ssh_option({connect_timeout, Value} = Opt) when is_integer(Value); Value
     Opt;
 handle_ssh_option({max_sessions, Value} = Opt) when is_integer(Value), Value>0 ->
     Opt;
+handle_ssh_option({max_channels, Value} = Opt) when is_integer(Value), Value>0 ->
+    Opt;
 handle_ssh_option({negotiation_timeout, Value} = Opt) when is_integer(Value); Value == infinity ->
     Opt;
 handle_ssh_option({parallel_login, Value} = Opt) when Value==true ; Value==false ->
diff --git a/lib/ssh/src/ssh_connection.erl b/lib/ssh/src/ssh_connection.erl
index 64d2113125..266c64fd4f 100644
--- a/lib/ssh/src/ssh_connection.erl
+++ b/lib/ssh/src/ssh_connection.erl
@@ -935,14 +935,27 @@ encode_ip(Addr) when is_list(Addr) ->
 	    end
     end.
 
-start_channel(Cb, Id, Args, SubSysSup) ->
-    start_channel(Cb, Id, Args, SubSysSup, undefined).
+start_channel(Cb, Id, Args, SubSysSup, Opts) ->
+    start_channel(Cb, Id, Args, SubSysSup, undefined, Opts).
 
-start_channel(Cb, Id, Args, SubSysSup, Exec) ->
+start_channel(Cb, Id, Args, SubSysSup, Exec, Opts) ->
     ChildSpec = child_spec(Cb, Id, Args, Exec),
     ChannelSup = ssh_subsystem_sup:channel_supervisor(SubSysSup),
+    assert_limit_num_channels_not_exceeded(ChannelSup, Opts),
     ssh_channel_sup:start_child(ChannelSup, ChildSpec).
     
+assert_limit_num_channels_not_exceeded(ChannelSup, Opts) ->
+    MaxNumChannels = proplists:get_value(max_channels, Opts, infinity),
+    NumChannels = length([x || {_,_,worker,[ssh_channel]} <- 
+				   supervisor:which_children(ChannelSup)]),
+    if 
+	%% Note that NumChannels is BEFORE starting a new one
+	NumChannels < MaxNumChannels ->
+	    ok;
+	true ->
+	    throw(max_num_channels_exceeded)
+    end.
+
 %%--------------------------------------------------------------------
 %%% Internal functions
 %%--------------------------------------------------------------------
@@ -998,9 +1011,11 @@ child_spec(Callback, Id, Args, Exec) ->
 
 start_cli(#connection{cli_spec = no_cli}, _) ->
     {error, cli_disabled};
-start_cli(#connection{cli_spec = {CbModule, Args}, exec = Exec,
+start_cli(#connection{options = Options,
+		      cli_spec = {CbModule, Args},
+		      exec = Exec,
 		      sub_system_supervisor = SubSysSup}, ChannelId) ->
-    start_channel(CbModule, ChannelId, Args, SubSysSup, Exec).
+    start_channel(CbModule, ChannelId, Args, SubSysSup, Exec, Options).
 
 start_subsytem(BinName, #connection{options = Options,
 				    sub_system_supervisor = SubSysSup},
@@ -1008,7 +1023,7 @@ start_subsytem(BinName, #connection{options = Options,
     Name = binary_to_list(BinName),
     case check_subsystem(Name, Options) of
 	{Callback, Opts} when is_atom(Callback), Callback =/= none ->
-	    start_channel(Callback, ChannelId, Opts, SubSysSup);
+	    start_channel(Callback, ChannelId, Opts, SubSysSup, Options);
 	{Other, _} when Other =/= none ->
 	    {error, legacy_option_not_supported}
     end.
diff --git a/lib/ssh/test/ssh_connection_SUITE.erl b/lib/ssh/test/ssh_connection_SUITE.erl
index fbcf06290a..37bba07440 100644
--- a/lib/ssh/test/ssh_connection_SUITE.erl
+++ b/lib/ssh/test/ssh_connection_SUITE.erl
@@ -48,7 +48,8 @@ all() ->
      gracefull_invalid_long_start,
      gracefull_invalid_long_start_no_nl,
      stop_listener,
-     start_subsystem_on_closed_channel
+     start_subsystem_on_closed_channel,
+     max_channels_option
     ].
 groups() ->
     [{openssh, [], payload() ++ ptty()}].
@@ -606,6 +607,78 @@ start_subsystem_on_closed_channel(Config) ->
     ssh:stop_daemon(Pid).
 
 %%--------------------------------------------------------------------
+max_channels_option() ->
+    [{doc, "Test max_channels option"}].
+
+max_channels_option(Config) when is_list(Config) ->
+    PrivDir = ?config(priv_dir, Config),
+    UserDir = filename:join(PrivDir, nopubkey), % to make sure we don't use public-key-auth
+    file:make_dir(UserDir),
+    SysDir = ?config(data_dir, Config),
+    {Pid, Host, Port} = ssh_test_lib:daemon([{system_dir, SysDir},
+					     {user_dir, UserDir},
+					     {password, "morot"},
+					     {max_channels, 3},
+					     {subsystems, [{"echo_n", {ssh_echo_server, [4000000]}}]}
+					    ]),
+
+    ConnectionRef = ssh_test_lib:connect(Host, Port, [{silently_accept_hosts, true},
+						      {user, "foo"},
+						      {password, "morot"},
+						      {user_interaction, true},
+						      {user_dir, UserDir}]),
+
+    {ok, ChannelId0} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, ChannelId1} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, ChannelId2} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, ChannelId3} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, ChannelId4} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, ChannelId5} = ssh_connection:session_channel(ConnectionRef, infinity),
+    {ok, _ChannelId6} = ssh_connection:session_channel(ConnectionRef, infinity),
+
+    %%%---- shell
+    ok = ssh_connection:shell(ConnectionRef,ChannelId0),
+    receive
+	{ssh_cm,ConnectionRef, {data, ChannelId0, 0, <<"Eshell",_/binary>>}} ->
+	    ok
+    after 5000 ->
+	    ct:fail("CLI Timeout")
+    end,
+
+    %%%---- subsystem "echo_n"
+    success = ssh_connection:subsystem(ConnectionRef, ChannelId1, "echo_n", infinity),
+
+    %%%---- exec #1
+    success = ssh_connection:exec(ConnectionRef, ChannelId2, "testing1.\n", infinity),
+    receive
+	{ssh_cm, ConnectionRef, {data, ChannelId2, 0, <<"testing1",_/binary>>}} ->
+	    ok
+    after 5000 ->
+	    ct:fail("Exec #1 Timeout")
+    end,
+
+    %%%---- ptty
+    success = ssh_connection:ptty_alloc(ConnectionRef, ChannelId3, []),
+
+    %%%---- exec #2
+    failure = ssh_connection:exec(ConnectionRef, ChannelId4, "testing2.\n", infinity),
+
+    %%%---- close the shell
+    ok = ssh_connection:send(ConnectionRef, ChannelId0, "exit().\n", 5000),
+    
+    %%%---- exec #3
+    success = ssh_connection:exec(ConnectionRef, ChannelId5, "testing3.\n", infinity),
+    receive
+	{ssh_cm, ConnectionRef, {data, ChannelId5, 0, <<"testing3",_/binary>>}} ->
+	    ok
+    after 5000 ->
+	    ct:fail("Exec #3 Timeout")
+    end,
+
+    ssh:close(ConnectionRef),
+    ssh:stop_daemon(Pid).
+
+%%--------------------------------------------------------------------
 %% Internal functions ------------------------------------------------
 %%--------------------------------------------------------------------
 big_cat_rx(ConnectionRef, ChannelId) ->