dirAccessPosix

fn dirAccessPosix(
    userdata: ?*anyopaque,
    dir: Dir,
    sub_path: []const u8,
    options: Dir.AccessOptions,
) Dir.AccessError!void {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    _ = t;

    var path_buffer: [posix.PATH_MAX]u8 = undefined;
    const sub_path_posix = try pathToPosix(sub_path, &path_buffer);

    const flags: u32 = @as(u32, if (!options.follow_symlinks) posix.AT.SYMLINK_NOFOLLOW else 0);

    const mode: u32 =
        @as(u32, if (options.read) posix.R_OK else 0) |
        @as(u32, if (options.write) posix.W_OK else 0) |
        @as(u32, if (options.execute) posix.X_OK else 0);

    const syscall: Syscall = try .start();
    while (true) {
        switch (posix.errno(posix.system.faccessat(dir.handle, sub_path_posix, mode, flags))) {
            .SUCCESS => {
                syscall.finish();
                return;
            },
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            else => |e| {
                syscall.finish();
                switch (e) {
                    .ACCES => return error.AccessDenied,
                    .PERM => return error.PermissionDenied,
                    .ROFS => return error.ReadOnlyFileSystem,
                    .LOOP => return error.SymLinkLoop,
                    .TXTBSY => return error.FileBusy,
                    .NOTDIR => return error.FileNotFound,
                    .NOENT => return error.FileNotFound,
                    .NAMETOOLONG => return error.NameTooLong,
                    .INVAL => |err| return errnoBug(err),
                    .FAULT => |err| return errnoBug(err),
                    .IO => return error.InputOutput,
                    .NOMEM => return error.SystemResources,
                    .ILSEQ => return error.BadPathName,
                    else => |err| return posix.unexpectedErrno(err),
                }
            },
        }
    }
}