Re: [PATCH 3/3] ALSA: core: set kcontrol's count field correctly

[Takashi Iwai <tiwai@suse.de>]

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:
> 
> 1. user reads the control element from kernel (the owner field is set)
> 2. user changes some values
> 3. 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.

What we need is the documentation of this feature...


thanks,

Takashi


> This patch fixes this issue.
> 
> Signed-off-by: Lu Guanqun <guanqun.lu@intel.com>
> ---
>  sound/core/control.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/sound/core/control.c b/sound/core/control.c
> index 98b7fc7..30e1483 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -1099,7 +1099,7 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
>  	if (err < 0)
>  		return err;
>  	memcpy(&kctl.id, &info->id, sizeof(info->id));
> -	kctl.count = info->owner ? info->owner : 1;
> +	kctl.count = info->count;
>  	access |= SNDRV_CTL_ELEM_ACCESS_USER;
>  	kctl.info = snd_ctl_elem_user_info;
>  	if (access & SNDRV_CTL_ELEM_ACCESS_READ)
>