Module commands

Introduced in MaxScale 2.1, the module commands are special, module-specific commands. They allow the modules to expand beyond the capabilities of the module API. Currently, only MaxCtrl implements an interface to the module commands.

All registered module commands can be shown with maxctrl list commands and they can be executed with maxctrl call command <module> <name> ARGS... where <module> is the name of the module and <name> is the name of the command. ARGS is a command specific list of arguments.

Developer reference

The module command API is defined in the modulecmd.h header. It consists of various functions to register and call module commands. Read the function documentation in the header for more details.

The following example registers the module command my_command for module my_module.

#include <maxscale/modulecmd.hh>

bool my_simple_cmd(const MODULECMD_ARG *argv)
{
    printf("%d arguments given\n", argv->argc);
}

int main(int argc, char **argv)
{
    modulecmd_arg_type_t my_args[] =
    {
        {MODULECMD_ARG_BOOLEAN, "This is a boolean parameter"},
        {MODULECMD_ARG_STRING | MODULECMD_ARG_OPTIONAL, "This is an optional string parameter"}
    };

    // Register the command
    modulecmd_register_command("my_module", "my_command", my_simple_cmd, 2, my_args);

    // Find the registered command
    const MODULECMD *cmd = modulecmd_find_command("my_module", "my_command");

    // Parse the arguments for the command
    const void *arglist[] = {"true", "optional string"};
    MODULECMD_ARG *arg = modulecmd_arg_parse(cmd, arglist, 2);

    // Call the module command
    modulecmd_call_command(cmd, arg);

    // Free the parsed arguments
    modulecmd_arg_free(arg);
    return 0;
}

The array my_args of type modulecmd_arg_type_t is used to tell what kinds of arguments the command expects. The first argument is a boolean and the second argument is an optional string.

Arguments are passed to the parsing function as an array of void pointers. They are interpreted as the types the command expects.

When the module command is executed, the argv parameter for the my_simple_cmd contains the parsed arguments received from the caller of the command.