Missing POSIX confstr and _CS_* symbols on Linux.

[jgarzik]

Apple Darwin provides the POSIX standard confstr(3) function and associated _CS_* symbols. Tested on Darwin and is working.

Requesting the same for Linux.

Quoting src/unix/bsd/apple/mod.rs:

// `confstr` keys (only the values guaranteed by `man confstr`).
pub const _CS_PATH: ::c_int = 1;
pub const _CS_DARWIN_USER_DIR: ::c_int = 65536;
pub const _CS_DARWIN_USER_TEMP_DIR: ::c_int = 65537;
pub const _CS_DARWIN_USER_CACHE_DIR: ::c_int = 65538;
...
    #[cfg_attr(
        all(target_os = "macos", target_arch = "x86"),
        link_name = "confstr$UNIX2003"
    )]
    pub fn confstr(name: ::c_int, buf: *mut ::c_char, len: ::size_t) -> ::size_t

The Linux version for this crate should be very similar. The Linux man page for confstr(3) also helpfully lists the few key _CS_* symbols that the developer should expect to be available:

       _CS_GNU_LIBC_VERSION (GNU C library only; since glibc 2.3.2)
       _CS_GNU_LIBPTHREAD_VERSION (GNU C library only; since glibc 2.3.2)
       _CS_PATH

[devnexen]

Would you be pleased to create a PR ?

[jgarzik]

@devnexen I gave it a shot with #3771, but I do not understand why the arm test is failing, so I'm a bit stuck.

[magicant]

For the libc-0.2 branch, #3612 is awaiting review.

[jgarzik]

For the libc-0.2 branch, #3612 is awaiting review.

Would it make sense to push to the main branch first, then backport once merged?

(I'm not familiar with this project's upstreaming flows)

[magicant]

I opened #3612 in the hope that 0.2.x would get released sooner than 1.0. If 1.0 is coming out soon, I'd retarget for the main branch. Any plans for future releases?

[jgarzik]

I opened #3612 in the hope that 0.2.x would get released sooner than 1.0. If 1.0 is coming out soon, I'd retarget for the main branch. Any plans for future releases?

Maybe I'm an old greybeard, but usually the norm is to post an upstream patch first, then backport to a branch once merged upstream, regardless of date when the next upstream release will come?

That way, the open source upstraming norm, nothing is lost when users transition from 0.2.x to 1.0.x.

[magicant]

I just followed the plan written in #3248. Not sure if the plan is still effective.