On Fri, Mar 30, 2007 at 11:56:28AM +0530, Rajat Jain wrote: > >> >> I was wondering that while using dynamic device numner allocation, can > >> >> we ever have a scenario like following (using alloc_chrdev_region): > >> >> > >> >> 1) Char Driver A is hooked on Major num X, minor numbers 0-10 > >> >> 2) Char Driver B is hooked on (same) Major num X, minor numbers 11-20 > >> > >> So the above is actually possible? > > > >Yes, once you have a major number, you can separate out the minor > >numbers how ever you wish to. > > Hi Greg, > > Ok, I understand that we can get a major number from the kernel and > split it into a range of minor numbers. > > But does alloc_chrdev_region() reuse the major numbers in such a way? > > In other words, is the following scenario possible: > > Driver 1 > ====== > alloc_chrdev_region(10 minor nos required) > -> receives major 150 (minor 0-9) > > Driver 2 > ====== > alloc_chrdev_region(20 minor nos required) > -> receives major 150 (minor 10-29) If you look at the code in fs/char_dev.c, this can not happen right now, however, that could change in the future if we start to see a lot of different drivers all want dynamic numbers. In short, don't count on the fact that you will always get a different major number, it is not guaranteed, and in fact, your driver should never care about such a thing. And also userspace doesn't care either, udev handles all of that logic for you automatically. Hope this helps, greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs
