uefi: Implement getcwd and chdir

[Ayush1325]

• Using EFI Shell Protocol. These functions do not make much sense unless a shell is present.
• Return the exe dir in case shell protocol is missing.

r? @joboet

[bors]

☔ The latest upstream changes (presumably #130724) made this pull request unmergeable. Please resolve the merge conflicts.

[Ayush1325]

ping @joboet

[joboet]

I'm very sorry for not getting back to you sooner.

The problem I see here is that GetCurDir returns a mapping, not a device path and will therefore not interoperate with our current filesystem implementation. I think there are two options we could take here:

1. Normalize the mapping to a device path using GetDevicePathFromMap
2. Use the filesystem functions from UEFI shell when available, which support both mappings and device paths.

Option 2 is more work, but has the advantage that File would support opening paths stored in environment variables, which will probably be mappings, not device paths, so I think that is the best option in the long run. If you want to get this PR merged first, then option 1 would also be fine for now.

[Ayush1325]

I'm very sorry for not getting back to you sooner.

It's fine. Everyone is doing stuff in their free time after all.

The problem I see here is that GetCurDir returns a mapping, not a device path and will therefore not interoperate with our current filesystem implementation. I think there are two options we could take here:

1. Normalize the mapping to a device path using GetDevicePathFromMap
2. Use the filesystem functions from UEFI shell when available, which support both mappings and device paths.

Option 2 is more work, but has the advantage that File would support opening paths stored in environment variables, which will probably be mappings, not device paths, so I think that is the best option in the long run. If you want to get this PR merged first, then option 1 would also be fine for now.

Thanks for pointing it out. I will add a TODO to implement it in the fs PR. Having support for mappings in file i/o is essential.

Personally, I would like to stick to the normal UEFI file APIs, and add plumbing in Rust side to handle the mapping to device path. It is fairly simple to do since we have edk2 as reference.

[joboet]

Right, then let's ship this.
@bors r+

[bors]

📌 Commit 1f718f9 has been approved by joboet

It is now in the queue for this repository.