cons is an interactive multiplexer for console in- and output. It buffers the output from different L4 clients and allows to switch between them to redirect input.

Multiplexers and Frontends

cons is able to connect multiple clients with multiple in/output servers.

Clients are handled by a multiplexer. Each multiplexer publishes a server capability that allows to create new client connections. The default multiplexer is normally known under the cons capability.

Actual in/output is handled by separate frontends. From the point-of-view of cons, a frontend consists of an IPC channel to a server that speaks an appropriate server protocol. By default the L4.Env.log capability is used.

For clients cons implements the L4::Vcon and the Virtio console interface. The supported frontends is limited to L4::Vcon only.

Starting the service

The cons server can be started with Lua like this:

local log_server = L4.default_loader:new_channel()
L4.default_loader:start({
  caps = {
    cons = log_server:svr(),
    fe = L4.Env.log,
  },
},
"rom/cons -m l4re -f fe")

First an IPC gate (log_server) is created which is used between the cons server and a client to request a new session. The server side is assigned to the mandatory cons capability of cons. The fe capability points to a L4::Vcon capable output.

Command Line Options

cons accepts the following command line switches:

-a, --show-all

Initially show output from all clients.
-B <size>, --defaultbufsize <size>

Default buffer size per client in bytes. Default: 40960
-c <client>, --autoconnect <client>

Automatically connect to the client with the given name. That means that output of this client will be visible and input will be routed to it.
-f <cap>, --frontend <cap>

Set the frontend for the current multiplexer. Output for the multiplexer is then sent to the capability with the given name. The server connected to the capability needs to understand the L4::Vcon protocol.
-k, --keep

Keep the console buffer when a client disconnects.
-l, --no-line-buffering

By default, merge the client output to entire lines. If the client writes characters without a final newline, the following client output is merged with the current line content. Specifying this switch disables the line buffered mode by default.
--line-buffering-ms <timeout>

Timeout in milliseconds before buffered client output is written even without a newline. Default value is 50.
-m <prompt name>, --mux <prompt name>

Add a new multiplexer named <prompt name>. This is necessary if output should be sent to different frontends.
-n, --defaultname

Default multiplexer capability to use. Default: cons.
-t, --timestamp

Prefix the output with timestamps.

Connecting a client

 create(backend_type, ["client_name"], ["color"], ["option"] [,"option"] ...)

backend_type

The type of backend that should be created for the client. The type is a positive integer and currently the following types are supported:
- L4.Proto.Log: L4::Vcon client
- 1: Virtio console client

cons accepts the following per-client options:

bufsz=n

Use a buffer of n bytes for this client, deviating from the default buffer size.
keep / no-keep

The console buffer is kept / thrown away when the client disconnects.
key=<key>

Assign <key> as keyboard shortcut to this client.
line-buffering / no-linux-buffering

Line buffering is enabled / disabled for this client.
show / hide

Output from this client is initially shown / hidden.
timestamp / no-timestamp

Do / do not prefix the output of this client with timestamps.