Re: [PATCH V3] brd: check and limit max_part par

Zhiqiang Liu
2020-01-20T13:15:03Z

On 2020/1/15 10:27, Ming Lei wrote:

>
>> MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
>>
>> unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
>> module_param(rd_size, ulong, 0444);
>> MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
>>
>> -static int max_part = 1;
>> -module_param(max_part, int, 0444);
>> +static unsigned int max_part = 1;
>> +module_param(max_part, uint, 0444);
>
> The above change isn't needed.
Thanks for your suggestion.
I will remove that in v4 patch.
>
>> MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");
>>
>> MODULE_LICENSE("GPL");
>> @@ -393,7 +393,14 @@ static struct brd_device *brd_alloc(int i)
>> if (!disk)
>> goto out_free_queue;
>> disk->major = RAMDISK_MAJOR;
>> - disk->first_minor = i * max_part;
>> + /*
>> + * Clear .minors when running out of consecutive minor space since
>> + * GENHD_FL_EXT_DEVT is set, and we can allocate from extended devt.
>> + */
>> + if ((i * disk->minors) & ~MINORMASK)
>> + disk->minors = 0;
>> + else
>> + disk->first_minor = i * disk->minors;
>
> The above looks a bit ugly, one nice way could be to change in
> brd_alloc():
>
> disk = brd->brd_disk = alloc_disk(((i * max_part) & ~MINORMASK) ?
> 0 : max_part);

I will change it as your suggestion.

>
>> disk->fops = &brd_fops;
>> disk->private_data = brd;
>> disk->queue = brd->brd_queue;
>> @@ -468,6 +475,21 @@ static struct kobject *brd_probe(dev_t dev, int *part, void *data)
>> return kobj;
>> }
>>
>> +static inline void brd_check_and_reset_par(void)
>> +{
>> + if (unlikely(!rd_nr))
>> + rd_nr = 1;
>
> zero rd_nr should work as expected, given user can create dev file via
> mknod, and brd_probe() will be called for populate brd disk/queue when
> the disk file is opened.
>
>> +static inline void brd_check_and_reset_par(void)
>> +{
>> +       if (unlikely(!rd_nr))
>> +               rd_nr = 1;
>> +
>> +       if (unlikely(!max_part))
>> +               max_part = 1;
>
> Another limit is that 'max_part' needs to be divided exactly by (1U <<
> MINORBITS), something like:
>
> max_part = 1UL << fls(max_part)

Do we have to limit that 'max_part' needs to be divided exactly by (1U <<
> MINORBITS)? As your suggestion, the i * max_part is larger than MINORMASK,
we can allocate from extended devt.

Thanks,
Zhiqiang Liu