Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote:
>Hi Yuanhan,
>
>On Tue, Jan 08, 2013 at 10:57:53PM +0800, Yuanhan Liu wrote:
>> The current kfifo API take the kfifo size as input, while it rounds
>> _down_ the size to power of 2 at __kfifo_alloc. This may introduce
>> potential issue.
>>
>> Take the code at drivers/hid/hid-logitech-dj.c as example:
>>
>> if (kfifo_alloc(&djrcv_dev->notif_fifo,
>> DJ_MAX_NUMBER_NOTIFICATIONS * sizeof(struct
>dj_report),
>> GFP_KERNEL)) {
>>
>> Where, DJ_MAX_NUMBER_NOTIFICATIONS is 8, and sizeo of(struct
>dj_report)
>> is 15.
>>
>> Which means it wants to allocate a kfifo buffer which can store 8
>> dj_report entries at once. The expected kfifo buffer size would be
>> 8 * 15 = 120 then. While, in the end, __kfifo_alloc will turn the
>> size to rounddown_power_of_2(120) = 64, and then allocate a buf
>> with 64 bytes, which I don't think this is the original author want.
>>
>> With the new log API, we can do like following:
>>
>> int kfifo_size_order = order_base_2(DJ_MAX_NUMBER_NOTIFICATIONS *
>> sizeof(struct dj_report));
>>
>> if (kfifo_alloc(&djrcv_dev->notif_fifo, kfifo_size_order,
>GFP_KERNEL)) {
>>
>> This make sure we will allocate enough kfifo buffer for holding
>> DJ_MAX_NUMBER_NOTIFICATIONS dj_report entries.
>
>Why don't you simply change __kfifo_alloc to round the allocation up
>instead of down?
>
>Thanks.
>
>--
>Dmitry
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Hi Dmitry,
I agree. I don't see the benefit in pushing up the change to a kfifo internal decision/problem to many different places in the kernel.
Regards,
Andy
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