proto/media: add LoadFile2Protocol

[RaitoBezarius]

The idea is to provide the LoadFile(2)Protocol family in uefi-rs with nice alloc helpers.

My goal is to use them as an alternative to the SimpleFilesystemProtocol when my bootloader is chained via PXE, which means that the SFS protocol is not available on the booted image handle, but… LoadFile(2)Protocol should, which enable me to continue downloading things like an initrd or a kernel as long as I know their exact paths.

This is a draft to open the discussion on the design.

https://uefi.org/specs/UEFI/2.10/13_Protocols_Media_Access.html#load-file-2-protocol

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[nicholasbishop]

Thanks, looks like a good addition to me. I've added a few comments.

[RaitoBezarius]

LoadFile(2)Protocol should, which enable me to continue downloading things like an initrd or a kernel as long as I know their exact paths.

Plot twist, after testing it for a while and reading the EDK2 source code, you will discover that the handle put on the thing responsible for an EFI PXE boot, which do have a LoadFileProtocol (and not a LoadFile2Protocol BTW), ignores completely the file path and calling LoadFile on it is restarting the PXE boot process.

So, it seems like the only reasonable way to download additional files yourself is to use the (M)TFTP services present on the EFI PXE base code protocol…

[RaitoBezarius]

Thanks for the review @nicholasbishop — I will work on it!

[phip1611]

Thanks for the review @nicholasbishop — I will work on it!

Any update here, @RaitoBezarius ?

[RaitoBezarius]

Thanks for the review @nicholasbishop — I will work on it!

Any update here, @RaitoBezarius ?

To be frank, I am a bit confused / blocked by the DevicePathProtocol API that seems different from the Ffi stuff I had and I don't think I can get it back in uefi-raw, so it is taking me time. If you want to finish it, please go for it, I may have too much on my plate right now…

[RaitoBezarius]

Right now, I am stuck on fixing some compilation issues, if anyone is interested to take over and I don't complete it in time, please go for it.

[phip1611]

Right now, I am stuck on fixing some compilation issues, if anyone is interested to take over and I don't complete it in time, please go for it.

...
#[unsafe_protocol(uefi_raw::protocol::media::LoadFile2::GUID)]
pub struct LoadFile2(uefi_raw::protocol::media::LoadFile2);
...

There is no uefi_raw::protocol::media::LoadFile2::GUID. If you add a new protocol, you need to add it at both places. uefi_raw for the low-level part and uefi for the high-level part. Similar to what happened here: https://github.com/rust-osdev/uefi-rs/pull/991/files

[RaitoBezarius]

Right now, I am stuck on fixing some compilation issues, if anyone is interested to take over and I don't complete it in time, please go for it.

...
#[unsafe_protocol(uefi_raw::protocol::media::LoadFile2::GUID)]
pub struct LoadFile2(uefi_raw::protocol::media::LoadFile2);
...

There is no uefi_raw::protocol::media::LoadFile2::GUID. If you add a new protocol, you need to add it at both places. uefi_raw for the low-level part and uefi for the high-level part. Similar to what happened here: #991 (files)

Yep, I just forgot to include the file, done.

[phip1611]

Any update here? We'd love to merge this