Added std.os.linux.sigtimedwait

[GrayHatter]

I wanted to name this fn sigTimedWait to match zig style. But decided not to given all (most?) other functions here duplicate the C-API style.

I'm not up to date on the current recommendations for how the stdlib should look. I considered introducing SigSet, as a full zig struct similar to the packed struct in std.os.linux.MAP but didn't here to keep this commit unobjectionable.

[alexrp]

Isn't this a classic case of programmer error?

[rootbeer]

According to #6389 this EINVAL should probably map to Unexpected? (I'm a fan of mapping the errnos 1:1 like the original PR here, but I believe 6389 is the current Zig plan of record.)

[GrayHatter]

Isn't this a classic case of programmer error?

That is more likely, but I'm not a fan of the current stdlib behavior of cutting it's own head off when something unexpected happens. I can replace this with invalidApiUsage() but I'd much rather expose the same API semantics that linux does. given this is a linux syscall.

Someone wanna make the call and I'll update the diff?

[GrayHatter]

An alternative would be using something like Io.Duration, and converting it internally. Then it's a prevented bug, instead of one that crashes the app... unless linux does something weird, and rejects a valid timeout?

[rpkak]

Functions in std.os.linux do not to switch on errno values. This function should probably just return sig_num as an usize and another function in std.os.linux.wrapped or std.posix can then call this function and switch on the errno.

[GrayHatter]

zig/lib/std/os/linux.zig

Line 1896 in 879ea27

else => |err| return std.os.unexpectedErrno(err),

zig/lib/std/os/linux.zig

Line 9908 in 73f863a

else => |err| return unexpectedErrno(err),

zig/lib/std/os/linux.zig

Line 9975 in 73f863a

else => |err| return unexpectedErrno(err),

I thought the exact same thing, but decided to keep it here mostly because posix as it is now isn't long for the repo.

[andrewrk]

please look around and follow the conventions from the surrounding code

[GrayHatter]

@andrewrk can I get a bit more of a hint about which direction you'd like to see the changes?

directly above the new fn is

pub fn gettid() pid_t {
    // Casts result to a pid_t, safety-checking >= 0, because gettid() cannot fail
    return @intCast(@as(u32, @truncate(syscall0(.gettid))));
}

and below is

pub fn sigaction(sig: SIG, noalias act: ?*const Sigaction, noalias oact: ?*Sigaction) usize {
  // ...
    if (E.init(result) != .SUCCESS) return result;

    if (oact) |old| {
        old.handler.handler = oldksa.handler;
        old.flags = oldksa.flags;
        old.mask = oldksa.mask;
    }

    return 0;
}

I believe that the shape of this function resembles the latter? Which convention would you prefer?