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L4Re Operating System Framework
Interface and Usage Documentation
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cons is an interactive multiplexer for console input and output. It buffers the output from different L4 clients and allows to switch between them to redirect input.
cons is able to connect multiple clients to multiple console I/O servers. All clients are connected to all configured multiplexers
Multiplexers and frontends come in pairs where the actual I/O is handled by the frontend. 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. Only frontends that speak the L4::Vcon protocol are supported.
A multiplexer handles and routes the I/O of each client to and from its respective frontend.
Each client's console settings (e.g. color, visibility) apply to all multiplexers and cannot be changed individually. A user can connect to all clients through all multiplexers. It is not possible to assign individual clients to distinct multiplexers.
For clients cons implements the L4::Vcon and the Virtio console interface. A client session can be requested through a create call to cons' factory. cons binds its factory capability to the cons capability. See the example below on how this can be set up.
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(), }, log = L4.Env.log, }, "rom/cons")
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. This example explicitly assigns the kernel's log capability (L4.Env.log) to cons' log capability in order to allow cons to provide input and output for its clients. The default log factory (usually provided by moe) doesn't provide input capabilities.
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 <cap>. 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. This option must be used in conjunction with the -f frontend option
-n, --defaultname
Default name for the multiplexer prompt. Default: cons.
-t, --timestamp
Prefix the output with timestamps.
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:
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.