Re: [PATCH] alternative dev patch

[Greg KH <greg@kroah.com>]

On Sat, Mar 22, 2003 at 02:02:00PM +0100, Roman Zippel wrote:
> > So only tty drivers currently do this.  But that might just be because
> > it's pretty hard to get a range of minors right now, as the api hasn't
> > been present.  Once we expand the range, I bet it will get quite common
> > (most character drivers only want from 1-16 minors normally.)
> 
> There are a few options:
> 1. Drivers can implement that themselves:

Yeah, but as I know, it's a big pain in the butt.  Let's make it easy to
do this, don't make writing a driver tougher than it has to be (it's
already much harder than it used to be.)  Andries's patch makes it easy,
which is a good thing in my book.

> a) The driver allocates the major itself and opens the real minor device 
> in its open function, (e.g. see the misc driver example). Especially tape 
> drivers have to do this anyway, because they encoded the open mode in 
> higher bits, so regions won't help you here at all.
> b) The driver allocates the major itself and installs the file_operations 
> directly in the char_device, e.g. that is something you might want to do 
> in the usb driver:
> 
> register_usb_device(...)
> {
> 	...
> 	cdev = cdget(dev);
> 	down(&cdev->sem);
> 	if (cdev->fops)
> 		...;
> 	cdev->fops = fops;
> 	up(&cdev->sem);
> }
> (see the misc driver again for a detailed example.)

Look at drivers/usb/core/file.c::usb_open(), it does much the same
thing.  Well, functionally the same, not identical in any way :)

thanks,

greg k-h