At Wed, 24 Aug 2011 14:17:57 +0800, Lu Guanqun wrote:
On Wed, Aug 24, 2011 at 02:06:34PM +0800, Takashi Iwai wrote:
At Wed, 24 Aug 2011 11:12:43 +0800, Lu Guanqun wrote:
I don't see how info's owner field relates to kcontrol's count field. It should assign to info's count instead.
Let's assume this scenario:
- user reads the control element from kernel (the owner field is set)
- user changes some values
- user issues 'SNDRV_CTL_IOCTL_ELEM_REPLACE' ioctl.
With the original code, 'kctl' here gets a large count number due to its non-empty owner field. Therefore it fails on subsequent call snd_ctl_new().
In IOCTL_ELEM_ADD and REPLACE, count and owner struct fields have different meanings from others. The count contains the array size, not the number of identical elements. And the owner contains the number of elements to be created. So, the current code is correct.
This sounds tricky...
in snd_ctl_elem_info(): info->owner = pid_vnr(vd->owner->pid); } else { info->owner = -1;
This is where owner of info get assigned, but it's not number of elements to be created.
The kcontrol.count field is never exposed to user-space.
I'm a bit unclear on this.
What we need is the documentation of this feature...
So my test case seems to be wrong, but how should I change it? Do I need to clear the owner field when user space application sends down the REPLACE ioctl?
Yes. Maybe it'd be better to define a new struct and use it in ADD/REPLACE ioctls so that user sees a clear difference. The struct will be identical except for renaming from owner to elem_count or such.
Takashi