dirCreateFile

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

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

    const os_flags: c.O = .{
        .ACCMODE = if (flags.read) .RDWR else .WRONLY,
        .NONBLOCK = flags.lock == .none or flags.lock_nonblocking,
        .SHLOCK = flags.lock == .shared,
        .EXLOCK = flags.lock == .exclusive,
        .CREAT = true,
        .TRUNC = flags.truncate,
        .EXCL = flags.exclusive,
        .CLOEXEC = true,
    };

    const fd: c.fd_t = while (true) {
        const rc = c.openat(dir.handle, sub_path_posix, os_flags, flags.permissions.toMode());
        switch (c.errno(rc)) {
            .SUCCESS => break @intCast(rc),
            .INTR => {},
            .FAULT => |err| return errnoBug(err),
            .INVAL => return error.BadPathName,
            .BADF => |err| return errnoBug(err), // File descriptor used after closed.
            .ACCES => return error.AccessDenied,
            .FBIG => return error.FileTooBig,
            .OVERFLOW => return error.FileTooBig,
            .ISDIR => return error.IsDir,
            .LOOP => return error.SymLinkLoop,
            .MFILE => return error.ProcessFdQuotaExceeded,
            .NAMETOOLONG => return error.NameTooLong,
            .NFILE => return error.SystemFdQuotaExceeded,
            .NODEV => return error.NoDevice,
            .NOENT => return error.FileNotFound,
            .NOMEM => return error.SystemResources,
            .NOSPC => return error.NoSpaceLeft,
            .NOTDIR => return error.NotDir,
            .PERM => return error.PermissionDenied,
            .EXIST => return error.PathAlreadyExists,
            .BUSY => return error.DeviceBusy,
            .OPNOTSUPP => return error.FileLocksUnsupported,
            .AGAIN => return error.WouldBlock,
            .TXTBSY => return error.FileBusy,
            .ROFS => return error.ReadOnlyFileSystem,
            .NXIO => return error.NoDevice,
            .ILSEQ => return error.BadPathName,
            else => |err| return unexpectedErrno(err),
        }
    };
    errdefer closeFd(fd);

    return .{
        .handle = fd,
        .flags = .{ .nonblocking = os_flags.NONBLOCK },
    };
}