At Wed, 24 Aug 2011 08:06:34 +0200, 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.
Correction: the count field means same as others. The info.count specifies the array size in IOCTL_ELEM_INFO, too. The only difference is an (ab)use of owner field.
Takashi