rust: add to_str and as_str_unchecked to CStr

[mdaverde]

Following the std::ffi::CStr pattern of to_str, this adds
methods to convert between CStr and &str both safely and unsafely

Closes #532

Signed-off-by: Milan Landaverde [email protected]

[ojeda]

A couple more nits:

• Please add intra-doc links wherever possible, e.g. in mentions to CStr and &str.
• In the commit message: the functions are about converting CStr to &str, not "between" (this does not matter much today, since the commit messages do not go into the kernel, but eventually they will! :)

[gurugio]

Hi,

I would like to run the unit-tests in your patch.
Could you please inform me how to run the unit-tests in the patch?
I knew how to run the unit-test in normal user-mode application with Rust
but I've not seen the unit-test in kernel code.

I have a VM running the kernel with Rust and loading the modules implemented with Rust.
I ran the user-mode application unit-test with VisualStudio and Cargo in the VM.
I guess it would be very different to run the unittest of kernel code.

[mdaverde]

From @ojeda

A couple more nits:

* Please add intra-doc links wherever possible, e.g. in mentions to `CStr` and `&str`.

Went ahead and added these

* In the commit message: the functions are about converting `CStr` to `&str`, not "between" (this does not matter much today, since the commit messages do not go into the kernel, but eventually they will! :)

Updated this commit message as well

[mdaverde]

From @gurugio

I would like to run the unit-tests in your patch. Could you please inform me how to run the unit-tests in the patch? I knew how to run the unit-test in normal user-mode application with Rust but I've not seen the unit-test in kernel code.

Hello! I've been running the tests with make LLVM=1 rusttest

[ojeda]

Looks good to me! Thanks for contributing!