Proposal: EFI boot stub configuration file

Proposal: EFI boot stub configuration file

[Shea Levy]

Hello,

In some EFI boot environments (e.g. booting from an external medium or 
non-standard systems where tools like efibootmgr don't work), it is 
currently impossible to pass the right arguments to the kernel unless an 
EFI shell is launched. To ameliorate this, I propose that if 
image->load_options_size is 0 (indicating no arguments were passed) AND 
image->parent_handle is NULL (indicating that the image was loaded 
automatically by the firmware), then the kernel looks for a file in some 
fixed, possibly configurable place (e.g. \efi\linux\params), sets 
image->load_options_size to its size, and sets image->load_options to 
its contents. On any error whatsoever (finding the file, reading it, 
getting its size, whatever), any allocated memory would be freed and 
load_options_size would be set back to 0. Since the arguments are 
already converted to ASCII and parsed during the boot process, the file 
would be expected to be in UCS-2 format and no validation would be done 
in the configuration loading code. I'll write something up over the next 
week or so and submit it as an RFC patch series, but I thought I'd post 
this here first in case anyone has immediate feedback based on this 
description.

Cheers,
Shea Levy

Re: Proposal: EFI boot stub configuration file

[H. Peter Anvin]

On 03/16/2012 02:25 PM, Shea Levy wrote:
> Hello,
> 
> In some EFI boot environments (e.g. booting from an external medium or
> non-standard systems where tools like efibootmgr don't work), it is
> currently impossible to pass the right arguments to the kernel unless an
> EFI shell is launched. To ameliorate this, I propose that if
> image->load_options_size is 0 (indicating no arguments were passed) AND
> image->parent_handle is NULL (indicating that the image was loaded
> automatically by the firmware), then the kernel looks for a file in some
> fixed, possibly configurable place (e.g. \efi\linux\params), sets
> image->load_options_size to its size, and sets image->load_options to
> its contents. On any error whatsoever (finding the file, reading it,
> getting its size, whatever), any allocated memory would be freed and
> load_options_size would be set back to 0. Since the arguments are
> already converted to ASCII and parsed during the boot process, the file
> would be expected to be in UCS-2 format and no validation would be done
> in the configuration loading code. I'll write something up over the next
> week or so and submit it as an RFC patch series, but I thought I'd post
> this here first in case anyone has immediate feedback based on this
> description.
> 

A file in UCS-2 seems messed up.

Otherwise, seems like a reasonable idea, with a major caveat... since
the whole point of this is to do something when it isn't possible to set
NVRAM variables, it would make most sense to me if the configuration
file could be founin a specific location relative to the kernel image
itself.

	-hpa

Re: Proposal: EFI boot stub configuration file

[Shea Levy]

On 3/16/12 5:28 PM, H. Peter Anvin wrote:
> A file in UCS-2 seems messed up. 

Yeah, it seemed like a good way to let the code be dumb but upon 
reflection it'd just be a confusing inefficiency.

> Otherwise, seems like a reasonable idea, with a major caveat... since 
> the whole point of this is to do something when it isn't possible to 
> set NVRAM variables, it would make most sense to me if the 
> configuration file could be founin a specific location relative to the 
> kernel image itself.

OK. I'll try both approaches to see if the code complexity is greatly 
increased in the relative path case.

Cheers,
Shea

Re: Proposal: EFI boot stub configuration file

[Shea Levy]

On 3/16/12 5:25 PM, Shea Levy wrote:
> the file would be expected to be in UCS-2 format

Actually, on second thought I could just add a check to see if the 
parent handle is NULL in an else if after the already-existing check to 
see if the command line options are NULL. Then the file can be expected 
to be ASCII.