LUA(4)

LUA(4) | Device Drivers Manual | LUA(4)

# NAME

`lua` — control in-kernel Lua states

# SYNOPSIS

`lua*`

`#include <sys/types.h>`
`#include <sys/lua.h>`

# DESCRIPTION

The `lua` device allows to create, control, and delete Lua states in the kernel through an ioctl(2) interface. Moreover, `lua` can be used to load Lua scripts into a Lua state and to assign modules to an existing state, i.e. perform the equivalent of the Lua command require. `lua` is also used to retrieve information about currently active Lua states.

# LUA MODULES

Lua modules are used to provide functionality to Lua scripts not available in the language itself, e.g. to access core kernel functionality like printing text on the console. Unlike in user space Lua, where Lua modules are files in the filesystem, modules must be provided to `lua` in the form of loadable kernel modules that register their functionality with `lua`. Modules are loaded using the `require` Lua command; whether this command is available or not is controlled by a sysctl(8) variable. `lua` by default tries to load a kernel module named luafoo.kmod when it encounters the Lua command require 'foo'.

# SYSCTL VARIABLES

The operation of `lua` can be controlled by means of the following sysctl(8) variables:

`kern.lua.autoload`
  When set to 1, `lua` tries to autoload kernel modules.

  The default value is 1.

`kern.lua.bytecode`
  When set to 1, loading of Lua bytecode is allowed.

  The default value is 0.

`kern.lua.maxcount`
  When set to a value > 0, `lua` limits the number of instructions executed to this number.

  The default value is 0.

`kern.lua.require`
  When set to 1, enables the require command in Lua.

  The default value is 1.

`kern.lua.verbose`
  When set to a value > 0, verbosity is increased.

  The default value is 0.

# IOCTL INTERFACE

The following structures and constants are defined in the `<sys/lua.h>` header file:

`LUAINFO(struct lua_info)`
  Returns information about the `lua` states in the lua_info structure:

      #define MAX_LUA_NAME		16
      #define MAX_LUA_DESC		64

      struct lua_state_info {
      	char	name[MAX_LUA_NAME];
      	char	desc[MAX_LUA_DESC];
      	bool	user;
      };

      struct lua_info {
      	int num_states;		/* total number of Lua states */
      	struct lua_state_info *states;
      };

`LUACREATE(struct lua_create)`
  Create a new named Lua state with name and description in the lua_create structure:

      struct lua_create {
      	char	name[MAX_LUA_NAME];
      	char	desc[MAX_LUA_DESC];
      };

`LUADESTROY(struct lua_create)`
  Destroy a named Lua state.

`LUAREQUIRE(struct lua_require)`
  Perform the equivalent of the Lua command require in a named state. The name of the state and of the module name is passed in the lua_require structure:

      #define LUA_MAX_MODNAME		32

      struct lua_require {
      	char	state[MAX_LUA_NAME];
      	char	module[LUA_MAX_MODNAME];
      };

`LUALOAD(struct lua_load)`
  Load Lua code from the filesystem into a named Lua state. The name of the state and the path to the Lua code are passed in the lua_load structure:

      struct lua_load {
      	char	state[MAX_LUA_NAME];
      	char	path[MAXPATHLEN];
      };

  The path element of the lua_load structure must contain at least one ‘/’ character.

# FILES

/dev/lua
  Lua device file.

# SEE ALSO

ioctl(2), luactl(8)

# HISTORY

The `lua` device first appeared in NetBSD 7.0.

# AUTHORS

The `lua` driver was written by Marc Balmer <mbalmer@NetBSD.org>.

# CAVEATS

The `lua` device is experimental. Incompatible changes might be made in the future.

July 25, 2014 | NetBSD 11.0