dirCreateFile

fn dirCreateFile(
    userdata: ?*anyopaque,
    dir: Dir,
    sub_path: []const u8,
    flags: Dir.CreateFileOptions,
) File.OpenError!File {
    const ev: *Evented = @ptrCast(@alignCast(userdata));

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

    var maybe_sync: CancelRegion.Sync.Maybe = .{ .cancel_region = .init() };
    defer maybe_sync.deinit(ev);
    const fd = ev.openat(&maybe_sync.cancel_region, dir.handle, sub_path_posix, .{
        .ACCMODE = if (flags.read) .RDWR else .WRONLY,
        .CREAT = true,
        .TRUNC = flags.truncate,
        .EXCL = flags.exclusive,
        .CLOEXEC = true,
    }, flags.permissions.toMode()) catch |err| switch (err) {
        error.OperationUnsupported => return error.Unexpected, // TMPFILE unset.
        else => |e| return e,
    };
    errdefer ev.closeAsync(fd);

    switch (flags.lock) {
        .none => {},
        .shared, .exclusive => try ev.flock(
            try maybe_sync.enterSync(ev),
            fd,
            flags.lock,
            if (flags.lock_nonblocking) .nonblocking else .blocking,
        ),
    }

    return .{ .handle = fd, .flags = .{ .nonblocking = false } };
}