How to get /dev entry created automaticly for dynamic major number?

[Markku Savela <msa@moth.iki.fi>]

If want to write a loadable module which "implements" a char device
("virtual", no real device present). How do I get the correct
"/dev/foo" to appear automaticly?  What is the current recommended
solution (kernel 2.6.17 in Ubuntu and later).

static int major;

static int __init foo_init(void)
    {
    ...
    major = register_chrdev(0, "foo", &fops);
    ....
    }

static void __exit foo_exit(void)
    {
    ...
    if (major > 0)
        unregister_chrdev(major, "foo");
    ...
    }

I thought that the above code would be enough to trigger the "udevd",
but apparently not (if it should, what is the match rule I have to
use? DRIVER=="foo" or KERNEL="foo[0-9]*"? None of these seem to
work). Do I have to do some additional poking with sysfs?  I can see
my module there, but nothing else.

The problem seems to be that most information I find from books or net
is out of date for 2.6, or carries note "these things are currently
been changed". A pointer to a definitive documentation would also do!