[ipxe-devel] [PATCH] [efi] make load file protocol optional

[Michael Brown]

On 12/02/15 14:41, Laszlo Ersek wrote:
> 1.5 After shim.efi is loaded (using EFI_LOAD_FILE_PROTOCOL, which
>      internally relies on EFI_PXE_BASE_CODE_PROTOCOL), shim.efi tries to
>      load further files, like grub<ARCH>.efi. For that it uses
>      EFI_PXE_BASE_CODE_PROTOCOL directly.
>
>      Please see findNetboot() and FetchNetbootimage() in "netboot.c".
>
>      (Requiring EFI_PXE_BASE_CODE_PROTOCOL is not unique to shim, see
>      another boot loader here:
>      <http://thread.gmane.org/gmane.comp.bios.tianocore.devel/12021>.)

OK, that makes sense now.  The issue is not (as reported) that iPXE's 
EFI_LOAD_FILE_PROTOCOL does not provide the ability to load arbitrary 
files; no other implementations of EFI_LOAD_FILE_PROTOCOL provide this 
ability, and nothing attempts to use EFI_LOAD_FILE_PROTOCOL in that way 
anyway.  Instead, the issue is that iPXE does not provide 
EFI_PXE_BASE_CODE_PROTOCOL and that other bootloaders assume that this 
protocol will be present.

> This issue might be fixable in several ways:
> (a) Rework edk2 to provide EFI_PXE_BASE_CODE_PROTOCOL independently of
>      EFI_LOAD_FILE_PROTOCOL.
>
> (b) Or, implement EFI_PXE_BASE_CODE_PROTOCOL in iPXE, and install it
>      alongside EFI_LOAD_FILE_PROTOCOL, in efi_snp_probe().
>
> (c) Or, drop EFI_LOAD_FILE_PROTOCOL from step 2.1 (dependent on build
>      time configuration).
>
> (d) Or, modify shim.efi, and possibly the other boot loader mentioned in
>      step 1.5, to use EFI_LOAD_FILE_PROTOCOL. This would also require all
>      relevant EFI_LOAD_FILE_PROTOCOL implementations to adhere to the
>      FilePath parameter.
>
> Option (c) is by far the least intrusive, and the proposed patch does
> that.

The problem is that option (c) also destroys the user's ability to use 
most features of iPXE.  It's a quick hack rather than a solution.

Option (d) sounds like the best idea, not least because it would allow 
for the use of non-braindead network protocols (i.e. almost anything 
except TFTP).  iPXE could quite easily have code in efi_snp_load_file() 
which would open and autoconfigure the network device, interpret 
FileName as a URI, and thereby allow shim.efi (or others) to download 
files via HTTP, HTTPS, etc.

Since EDK2 implementations of EFI_LOAD_FILE_PROTOCOL (also) do not 
conform to the UEFI specification, shim.efi should probably retain the 
ability to fall back to EFI_PXE_BASE_CODE_PROTOCOL if 
EFI_LOAD_FILE_PROTOCOL returns EFI_UNSUPPORTED.

Thoughts?

Michael