#24471: add mlock syscalls in std.os.linux

[jeffective]

closes #24471

MCL Flags

Please double-check the implementation of MCL. I interpreted results of searching the linux source tree:
https://github.com/search?q=repo%3Atorvalds%2Flinux+MCL_ONFAULT&type=code

I found the flags by referencing man mlock: https://man7.org/linux/man-pages/man2/mlock.2.html

Verification evidence

• on WSL2 on windows

Create file mlock-test.zig:

const std = @import("std");

test "mlock syscalls" {
    const allocator = std.testing.allocator;
    const my_memory_area: []u8 = try allocator.alloc(u8, 2048);
    defer allocator.free(my_memory_area);

    const mlock_result = std.os.linux.mlock(my_memory_area.ptr, my_memory_area.len);
    std.log.warn("mlock errno: {}", .{std.posix.errno(mlock_result)});
    try std.testing.expect(mlock_result == 0);

    const munlock_result = std.os.linux.munlock(my_memory_area.ptr, my_memory_area.len);
    std.log.warn("munlock errno: {}", .{std.posix.errno(munlock_result)});
    try std.testing.expect(munlock_result == 0);

    const mlock2_result = std.os.linux.mlock2(my_memory_area.ptr, my_memory_area.len, std.os.linux.MLOCK{ .ONFAULT = false });
    std.log.warn("mlock2 errno: {}", .{std.posix.errno(mlock2_result)});
    try std.testing.expect(mlock2_result == 0);

    const munlock_result2 = std.os.linux.munlock(my_memory_area.ptr, my_memory_area.len);
    std.log.warn("munlock errno: {}", .{std.posix.errno(munlock_result2)});
    try std.testing.expect(munlock_result2 == 0);

    const mlockall_result = std.os.linux.mlockall(std.os.linux.MCL{ .CURRENT = true });
    std.log.warn("mlockall errno: {}", .{std.posix.errno(mlockall_result)});
    try std.testing.expect(mlockall_result == 0);

    const munlockall_result = std.os.linux.munlockall();
    std.log.warn("munlockall errno: {}", .{std.posix.errno(munlockall_result)});
    try std.testing.expect(munlockall_result == 0);
}

Run using zig built from source at commit 7caf40b (this PR)

janderson@DESKTOP-RN10O9U:~/repos/untracked$ sudo ../zig/build/stage3/bin/zig test --zig-lib-dir /home/janderson/repos/zig/lib/ mlock-test.zig
[default] (warn): mlock errno: .SUCCESS
[default] (warn): munlock errno: .SUCCESS
[default] (warn): mlock2 errno: .SUCCESS
[default] (warn): munlock errno: .SUCCESS
[default] (warn): mlockall errno: .SUCCESS
[default] (warn): munlockall errno: .SUCCESS
All 1 tests passed.

Prior Art

https://github.com/tigerbeetle/tigerbeetle/blob/41c9a90dd930d360914f96bb2bd8a46d0ea2104d/src/stdx/mlock.zig#L29

[rootbeer]

This looks like a reasonable addition to the ZIg linux syscall wrappers. I've got a couple notes, but feel free to ignore me as I'm just a drive-by reviewer.

In addition to the notes below, I also suggest adding some very simple tests. Its okay if they just return EPERM or EINVAL for the calls, the important thing is to make sure the wrapper code is at least compiled, as unreached code is ignored.

[rootbeer]

Fixes LGTM.

[jeffective]

In addition to the notes below, I also suggest adding some very simple tests. Its okay if they just return EPERM or EINVAL for the calls, the important thing is to make sure the wrapper code is at least compiled, as unreached code is ignored.

Will wait for additional guidance on this from core team

[blblack]

I'd love to see these implemented as well (and std.c equivalents, and std.posix wrappers, but those could come separately/after this).

@jeffective - feel free to compare/steal anything from my abandoned old draft PR here (this was from before the std.os/posix re-org, no longer directly-applicabe) - https://github.com/ziglang/zig/pull/19203/commits