Replace `kernel::str::CStr` by `core::ffi::CStr`

[y86-dev]

std::ffi::CStr was moved to core::ffi::CStr in rust 1.64, making it available to the kernel. We have our own version of CStr in kernel::str, since the standard library one wasn't available. Rust 1.77 also added C-string literals c"abc" that automatically terminate strings with \0. The kernel has a c_str! macro for this purpose. We should use the types from the standard library and remove our own versions. The things to do would be

• change uses of kernel::str::CStr to core::ffi::CStr and also change c_str!("...") into c"..."
• remove kernel::str::CStr and the macro

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This requires submitting a proper patch to the LKML and the Rust for Linux mailing list. Please recall to test your changes, to use a proper title for the commit, to sign your commit under the Developer's Certificate of Origin and so on. Please see https://docs.kernel.org/process/submitting-patches.html and https://rust-for-linux.com/contributing for details.

Please take this issue only if you are new to the kernel development process and you would like to use it as a test to submit your first patch to the kernel. Please do not take it if you do not plan to make other contributions to the kernel.

[vincenzopalazzo]

I will look into it 😸

[y86-dev]

We try to give good-first-issues to people who do not yet have commits in the kernel. It helps folks getting familiar with the kernel development process. We also try to pick easy/trivial fixes as good-first-issues. AFAIK you already submitted a good-first-issue, so it would be best to leave this up to someone else :)

[vincenzopalazzo]

Make sense!

[vadorovsky]

I can take it.

[Steffo99]

Hi!

I'd be interested in taking this issue to both learn to contribute to Rust for Linux and to submit my first patch to the Linux kernel, which is a requirement to pass the Kernel Hacking university course I've been attending.

@vadorovsky, are you still working on it?
(I'm sending you a ping on the Fediverse too as soon as I post this, just to make sure that you see it...)

Can I take this issue?

[Steffo99]

Got an answer by @vadorovsky on the Fediverse!

Seems like he's still working on it :)

I'll look for another issue!

[vadorovsky]

Yes, I'm still working on it. Here is my WIP branch: https://gitlab.com/vadorovsky/linux/-/commits/rust-cstr

Before sending it, I still want to polish it a bit. I'm also thinking how to handle the fact that alloc::CString doesn't have any equivalent of try_from_fmt, but my idea for now is to add CStringExt. I'm coding it right now. If I'm happy from the result, I will add it and send it to the ML.

[vadorovsky]

Sent a patch, only with CStr removal:

https://lore.kernel.org/rust-for-linux/20240714160238.238708-1-vadorovsky@gmail.com/T/#u