linux-kernel - Re: [PATCH 5/5] drivers: char: Replace bit operation functions with IDA allocator.

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Date:   Sun, 9 Apr 2017 10:50:25 +0530
From:   Varsha Rao <rvarsha016@...il.com>
To:     Matthew Wilcox <mawilcox@...rosoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] drivers: char: Replace bit operation functions with
 IDA allocator.

>> Replace bit operation functions with IDA allocator functions. As IDA
>> allocation is simpler.
>
> But why does this matter?

Few of the files in this driver is already using ida allocation. For maintaining
the uniformity I have used ida allocation.

Files using idr-ida interface
hw_random/virtio-rng.c
tpm/tpm-chip.c
ppdev.c
tpm/tpm-interface.c
tpm/tpm.h

>>       if (is_dynamic) {
>> -             int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
>> +             int i = ida_simple_get(&misc_minors_ida, 0,
>> +                                    DYNAMIC_MINORS, GFP_KERNEL);
>>
>>               if (i >= DYNAMIC_MINORS) {
>>                       err = -EBUSY;
>>                       goto out;
>> -             }
>> +             } else if (i < 0) {
>> +                     err = i;
>> +                     goto out;
>> +             } else {
>>               misc->minor = DYNAMIC_MINORS - i - 1;
>> -             set_bit(i, misc_minors);
>> +             }
>
> Your indentation is now incorrect :(

I don't know but in the patch it has correct indentation as below.
-               set_bit(i, misc_minors);
+               }
      } else {
                struct miscdevice *c;


>>       } else {
>>               struct miscdevice *c;
>>
>> @@ -222,7 +226,7 @@ int misc_register(struct miscdevice *misc)
>>                       int i = DYNAMIC_MINORS - misc->minor - 1;
>>
>>                       if (i < DYNAMIC_MINORS && i >= 0)
>> -                             clear_bit(i, misc_minors);
>> +                             ida_simple_remove(&misc_minors_ida, i);
>>                       misc->minor = MISC_DYNAMIC_MINOR;
>>               }
>>               err = PTR_ERR(misc->this_device);
>> @@ -258,7 +262,7 @@ void misc_deregister(struct miscdevice *misc)
>>       list_del(&misc->list);
>>       device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
>>       if (i < DYNAMIC_MINORS && i >= 0)
>> -             clear_bit(i, misc_minors);
>> +             ida_simple_remove(&misc_minors_ida, i);
>
> As much as I like the ida interface, I don't see why it is required to
> use it here, you have not provided any justification for this patch at
> all :(

Here by the usage of ida interface, allocation will be simpler, faster and
more space efficient. Also conversion  to it is simple. As I mentioned
earlier in this mail also to maintain uniformity of the driver.

Thanks,
Varsha Rao