Re: alloc_chrdev_region/unregister_chrdev_region - Issue

[Alexander Potashev <aspotashev@xxxxxxxxx>]

Hello!

> >>>>  /* temporary */
> >>>>  96         if (major == 0) {
> >>>>  97                 for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
> >>>>  98                         if (chrdevs[i] == NULL)
> >>>>  99                                 break;
> >>>> 100                 }
> >>>> 101
> >>>> 102                 if (i == 0) {
> >>>> 103                         ret = -EBUSY;
> >>>> 104                         goto out;
> >>>> 105                 }
> >>>> 106                 major = i;
> >>>> 107                 ret = major;
> >>>> 108         }
> >>>> 109
> >>>>
> >>>> REF: http://lxr.oss.org.cn/source/fs/char_dev.c#L80

You should probably use another Linux source code lxr, lxr.oss.org.cn
is outdated and not working at the moment.

> >>>> > On seeing the code (unregister_chrdev_region) it seems that it
> >>>> > just
> >>>> > kfree
> >>>> > the chrdevs[] entry but not set it to NULL which cause for new
> >>>> > entry in chrdevs[].

AFAIU, chrdevs is an array of singly-linked lists
('struct char_device_struct' even has a 'next' entry). When unregistering
a char dev region, __unregister_chrdev_region deletes an entry from one
list. If that entry was the last entry in the list, the corresponding
chrdevs[i] becomes NULL.

REF: http://lxr.linux.no/linux+v2.6.27.9/fs/char_dev.c#L179

> >> This issue is resolved, problem is indeed in my driver cleanup function.
> >> unregister_chrdev_region(
> >> MAJOR(cmos_dev_number), NUM_CMOS_BANKS);
> >> Instead of passing MAJOR(cmos_dev_number) passing 'cmod_dev_number' works.

Yes, unregister_chrdev_region's first argument is 'dev_t from', therefore
you should use 'cmod_dev_number'.

					Alexander

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