Re: [REVIEWv3 PATCH 09/13] vb2: add vb2_fileio_is_active and check it more often

[Hans Verkuil <hansverk@cisco.com>]

On 04/11/2014 03:05 PM, Tomasz Stanislawski wrote:
> Hi Hans,
> 
> On 04/11/2014 10:11 AM, Hans Verkuil wrote:
>> From: Hans Verkuil <hans.verkuil@cisco.com>
>>
>> Added a vb2_fileio_is_active inline function that returns true if fileio
>> is in progress. Check for this too in mmap() (you don't want apps mmap()ing
>> buffers used by fileio) and expbuf() (same reason).
> 
> Why? I expect that there is no sane use case for using
> mmap() and expbuf in read/write mode but why forbidding this.
> 
> Could you provide a reason?

The buffer management is completely internal to vb2 for read()/write().
I think that allowing expbuf/mmap is just plain weird. I don't think
it would do any harm other than increasing the memory refcount, but
I very much prefer to block this.

The only ioctl allowed is querybuf, and that primarily for debugging.
Frankly, I wouldn't mind if that is blocked off as well but since it
is guaranteed to have no side-effects and it actually has a use-case
(debugging) I've left that in.

Personally I think the question is not: "why block this?", it is:
"why would you allow it?".

Regards,

	Hans