Re: How to use grub2-extra-lua module

[Geoffrey Thomas]

On Thu, 15 May 2014, 张驰 wrote:

> I googled for grub2-lua, but found very few information on it. I can't 
> find an official website for grub2-lua (i.e official stable source code 
> tarball download link), except for a git/bzr clone link.
>
> Moreover, I can't find any documentation about grub lua. So I don't know 
> how to use it.
>
> I managed to compile grub2 along with lua module, then I boot into grub 
> and type "help lua" to try to get some help info. But it only says that 
> I can use command "lua script_file.lua" to execute the lua script. So I 
> just want to learn the details on how to use lua module. For example, 
> how to execute lua commands in grub.cfg file, how to return the lua 
> execution result to the grub.cfg file, and what APIs does grub provide 
> to the lua module.
>
> The reason why I want to use lua module is that I have the need of file 
> system operations in grub (i.e. mv, cp, cd, pwd, mkdir, rm, nano 
> commands). grub2 itself doesn't provide this functionality. Some posts 
> said grub-extra-lua module may provide this feature.
>
> So I just want to know how to use grub lua module to operate on files 
> and directories.

Take a look at the grub_lua_lib array at the bottom of grub_lib.h. Those 
functions are accessible in the "grub" library. Any GRUB command can be 
accessed via grub.run; for instance, grub.run("boot") will boot the loaded 
kernel. Many GRUB commands have return values, which are returned from 
grub.run.

You can use the grub.file_* functions for opening files. For instance, you 
can write local f = grub.file_open("/boot/myfile.txt", "r") to get a file 
handle, and then call grub.file_getline(f) to read lines from the file.

GRUB generally tries to avoid writing to disks, mostly because safely 
writing to disks is much harder than safely reading from them, especially 
if an fsck is needed. So you're probably not going to get mv, cp, rm, etc. 
If you need to set persistent settings, you may be interested in the 
environment block functionality. You can read and write variables via 
grub.getenv and grub.setenv, and load and store the enviornment block via 
grub.run("load_env") and grub.run("save_env"). See
http://www.gnu.org/software/grub/manual/html_node/Environment-block.html
for more details.

Hope this helps,
--
Geoffrey Thomas
address@hidden