i'm in the midst of updating some basic kernel documentation and i just ran across something that makes me question my understanding of the alloc_chrdev_region() kernel routine. as i've understood it all this time, that routine is the preferred routine if you want to allocate some character devices *dynamically* -- that is, to accept whatever major number(s) the kernel is willing to hand back. with that routine, you're not supposed to *specify* a major number that you want, you just accept what you're given. at least that's what i always thought. i was perusing the kernel source looking for a simple driver example that used that routine, and found drivers/char/bsr.c, but the init routine looks weird, as in: ===== static int __init bsr_init(void) { struct device_node *np; dev_t bsr_dev = MKDEV(bsr_major, 0); <--- ???????? int ret = -ENODEV; int result; np = of_find_compatible_node(NULL, NULL, "ibm,bsr"); if (!np) goto out_err; bsr_class = class_create(THIS_MODULE, "bsr"); if (IS_ERR(bsr_class)) { printk(KERN_ERR "class_create() failed for bsr_class\n"); goto out_err_1; } bsr_class->dev_attrs = bsr_dev_attrs; result = alloc_chrdev_region(&bsr_dev, 0, BSR_MAX_DEVS, "bsr"); bsr_major = MAJOR(bsr_dev); ===== note that early declaration of "dev_t bsr_dev". why is it being initialized to what is an uninitialized static variable much earlier in that source file? the value of "bsr_major" certainly isn't used until it's *assigned* in the call: result = alloc_chrdev_region(&bsr_dev, 0, BSR_MAX_DEVS, "bsr"); bsr_major = MAJOR(bsr_dev); as best as i can tell, that initial declaration can simply be: dev_t bsr_dev; i see no reason to initialize it to anything since alloc_chrdev_region() is supposed to treat the dev_t parameter as output only, is it not? am i missing something here? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Tw itter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================