On Wed, Mar 05, 2025 at 07:18:33PM -0500, Felix Kuehling wrote: > > On 2025-03-05 16:08, Salah Triki wrote: > > Replace (un)register_chrdev() by (unregister/alloc)_chrdev_region() as > > they are deprecated since kernel 2.6. > > Where is that information coming from? I see __register_chrdev documented in > the current kernel documentation. I see no indication that it's deprecated: > https://docs.kernel.org/core-api/kernel-api.html#c.__register_chrdev > In the book "Linux Device Drivers" 3ed of J. Corbet and al. (2005), it is indicated that using register_chrdev() is the old way to register char drivers, the new code should not use this interface, it should instead use the cdev interface. > > > alloc_chrdev_region() generates a > > dev_t value, so replace the kfd_char_dev_major int variable by the > > kfd_char_dev_id dev_t variable and drop the MKDEV() call. Initialize a > > cdev structure and add it to the device driver model as register_chrdev() > > used to do and since alloc_chrdev_region() does not do it. Drop the > > iminor() call since alloc_chrdev_region() allocates only one minor number. > > On error and in the module exit function, remove the cdev structure from > > the device driver model as unregister_chrdev() used to do. > > Sounds complicated. Your patch seems to open-code a bunch of details that > are neatly hidden inside register_chrdev. Why would I want all that detail > in my driver? I don't see an obvious advantage. > register_chrdev() registers 256 minor numbers, calling it will result in calling kmalloc_array(256, sizeof(struct probe), GFP_KERNEL) whereas calling alloc_chrdev_region() with count parameter equals to 1, which is the number of minor numbers requested, will result in calling kmalloc_array(1, sizeof(stuct probe), GFP_KERNEL). Best Regards, Salah Triki
