Am 07.03.25 um 20:10 schrieb Salah Triki: > 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. Yeah, but that doesn't count. Only in kernel documentation is relevant. Regards, Christian. >>> 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
