Re: [PATCH for-next V1 2/5] IB/core: Add ib_is_udata_cleared

[Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 10/12/2015 16:59, Matan Barak wrote:
> On Mon, Dec 7, 2015 at 3:18 PM, Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> wrote:
>> On 12/03/2015 05:44 PM, Matan Barak wrote:
>>> Extending core and vendor verb commands require us to check that the
>>> unknown part of the user's given command is all zeros.
>>> Adding ib_is_udata_cleared in order to do so.
>>>
>>
>> Why not copy the data into kernel space and run memchr_inv() on it?
>>
> 
> Probably less efficient, isn't it?
Why do you think it is less efficient?

I'm not sure calling copy_from_user multiple times is very efficient.
For once, you are calling access_ok multiple times. I guess it depends
on the amount of data you are copying.

> I know it isn't data path, but we'll execute this code in all extended
> functions (sometimes even more than once).
Do you think it is important enough to maintain our own copy of
memchr_inv()?

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