On 9/13/19 12:12 PM, Matthew Wilcox wrote:
> On Fri, Sep 13, 2019 at 11:57:17AM -0300, André Almeida wrote:
>> On 9/12/19 7:20 PM, Chaitanya Kulkarni wrote:
>>> On 09/12/2019 03:09 PM, André Almeida wrote:
>>>> Hello Matthew,
>>>>
>>>> On 9/12/19 1:19 PM, Matthew Wilcox wrote:
>>>>> On Wed, Sep 11, 2019 at 11:46:36AM -0300, André Almeida wrote:
>>>>>>
>>>>>> -static int nr_devices = 1;
>>>>>> +static unsigned int nr_devices = 1;
>>>>>> module_param(nr_devices, int, 0444);
>>>>>
>>>>> ^^^ you forgot to change the module_param to match
>>>>>
>>>>>> + if (!nr_devices) {
>>>>>> + pr_err("null_blk: invalid number of devices\n");
>>>>>> + return -EINVAL;
>>>>>> + }
>>>>>
>>>>> I don't think this is necessary.
>>>>>
>>>>
>>>> Could you explain why you don't think is necessary? As I see, the module
>>>> can't be used without any /dev/nullb* device, so why we should load it?
>>>>
>>>> Thanks,
>>>> André
>>>>
>>>
>>> I think Matthew is right here. I think module can be loaded with
>>> nr_devices=0.
>>>
>>> Did you get a chance to test nr_device=0 condition ?
>>>
>>
>> Yes. It says "module loaded" and lsmod shows that it is loaded indeed.
>> But you don't have any /dev/nullb*, so you can't do much with the module.
>>
>> With this patch, it refuses to load the module.
>
> Why is that an improvement? I agree it's an uninteresting thing to ask
> for, but I don't see a compelling need to fail the module load because
> of it.
>
Indeed, failing is used when there is something wrong with the module,
and this is not the case when (nr_devices == 0). I will remove this, thanks!
>> I did not tested with all possible conditions, but I tested with the
>> following ones:
>>
>> * Using a negative number of devices:
>> - Previously, it would alloc and add a huge number of devices until the
>> system gets out of memory
>> - With module_param as uint, it will throw a "invalid for parameter
>> `nr_devices'" and refuse to load
>>
>> * Using a range of values (1, 10, 100, 1000):
>> - It will works as expect, creating some /dev/nullbX accordingly with
>> your parameter. Works fine with and without this patch.
>
> If you ask it to create 4 billion devices, what happens? Obviously we'll
> run out of dev_t at some point ...
>
