Refactor libc pipe tests to use utility functions for error handling and data operations

[hulxv]

Related to #4725

[rustbot]

Thank you for contributing to Miri! A reviewer will take a look at your PR, typically within a week or two.
Please remember to not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.

[RalfJung]

Thanks a lot! This looks great.

However, there are some read calls here you did not convert because we did not have the right helpers for that. I think we should explore adding more helpers so that we don't need to do a second pass over all the tests later.

View changes since this review

[RalfJung]

We should think about a way to also cover this case without having to directly invoke read (or read_all below).

I am imagining functions like this:

/// Fill `dest` by repeatedly reading from `fd`. Error if not enough bytes could be read.
fn read_all_into_slice(fd: libc::c_int, dest: &mut [u8]) -> Result<(), libc::ssize_t>;

/// Read up to `dest.len()` many bytes from `fd`. Returns a pair of the part of `dest` that has been
/// read into, and the tail that was left untouched.
fn read_into_slice(fd: libc::c_int, dest: &mut [u8]) -> Result<(&mut [u8], &mut [u8]), libc::ssize_t>;

Can you add such functions to tests/utils/libc.rs and use them here?

(Please let me know if this is too much, then I can take over for this part.)

[hulxv]

It seems clear. I will do changes very soon because currently I am busy with my exams but don't worry, I will do it!

Do you want to use these functions instead of read and read_all in all libc tests? also maybe adding them to all PRs do some conflicts so is there a way to avoid this? maybe open a separate pr?

[RalfJung]

This PR should use functions like that for all read in the pipe tests. Once this lands, the function is then available for the other PRs, so that should avoid conflicts.

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[RalfJung]

I can't tell if you intend to make more changes here or not -- as indicated above, I will wait until you mark this PR as ready before I do another review.

[hulxv]

@rustbot ready

[hulxv]

Sorry, It seems the test fails without noticing it. it's fixed now

[RalfJung]

Thanks! I made some further small tweaks, this is good to land now. :)

resolved