Linux: add getitimer()/setitimer()

[nathaniel-bennett]

Resolves #1347

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[devnexen]

not sure I follow, why not using the typedef you created above ?

[nathaniel-bennett]

This is the result of a strange combination of issues. glibc and most other libc implementations typedef __itimer_which_t as an enum when _GNU_SOURCE is set, or as an int otherwise. musl unfortunately opts to just use an int directly within the function definitions for getitimer and setitimer. As a result of this:

• Using __itimer_whiich_t directly in function definitions causes musl CI to fail as it's not a defined type
• Removing __itimer_which_t altogether for musl builds still causes CI to fail, as there is currently no way of opting out of enum semver checks (you can opt out for structs, types, everything else but enums)

By defining __itimer_which_t as a type definition in musl and then opting out of it, CI passes.

A more clean solution to this may be to develop enum opt-out functions to the ctest2 crate.

[devnexen]

Another possible approach is not to bother with enums at all.

pub type __itimer_which_t = ::c_int;
...
pub const ITIMER_REAL: __itimer_which_t = 0;
...

There are various places in this crate were C enums are handled as simple constants. Should pass in theory.

[nathaniel-bennett]

r? @tgross35