Rethink (im)mutabiltiy of device paths (`DevicePathBuilder` / `install_protocol_interface`)

[phip1611]

DevicePathBuilder::finalize() returns a &DevicePath. If one wants to install this to a handle using install_protocol_interface, one has to cast that to a *mut c_void. It feels unhandy to change the mutability here.

Also, I'm not sure if install_protocol_interface could just consume a *const`. In the spec, I don't find something that says that this needs to be mutable:

https://uefi.org/specs/UEFI/2.10/07_Services_Boot_Services.html?highlight=install_protocol_interface

Code that uses this functionality can be found here: nix-community/lanzaboote#194

[blitz]

It would be nice to be able to build device paths as global constants as well. This would sidestep the use-after-free issues from nix-community/lanzaboote#194.

[phip1611]

🔝 I wonder if this is possible without (procedural) macros but only const functions 🤔

I have to take a closer look at device paths.

[nicholasbishop]

I agree with you that install_protocol_interface could just take a const pointer. Put up #981 for that.

Interesting idea about constructing const device paths. It's tricky in the general case since some nodes are rather dynamic. We'd also have to change our current trait-based approach (https://docs.rs/uefi/latest/uefi/proto/device_path/build/trait.BuildNode.html), since I don't think there's any way to declare const fns in traits yet.

[nicholasbishop]

I opened #983 for building device paths as constants. install_protocol_interface & co have been updated to take a const pointer, so closing this issue.