Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case

[Jaroslav Kysela <perex@perex.cz>]

Dne 23. 12. 19 v 10:33 Takashi Sakamoto napsal(a):
> A design of ALSA control core allows applications to execute three
> operations for TLV feature; read, write and command. Furthermore, it
> allows driver developers to process the operations by two ways; allocated
> array or callback function. In the former, read operation is just allowed,
> thus developers uses the latter when device driver supports variety of
> models or the target model is expected to dynamically change information
> stored in TLV container.
> 
> The core also allows applications to lock any element so that the other
> applications can't perform write operation to the element for element
> value and TLV information. When the element is locked, write and command
> operation for TLV information are prohibited as well as element value.
> Any read operation should be allowed in the case.
> 
> At present, when an element has callback function for TLV information,
> TLV read operation returns EPERM if the element is locked. On the
> other hand, the read operation is success when an element has allocated
> array for TLV information. In both cases, read operation is success for
> element value expectedly.
> 
> This commit fixes the bug. This change can be backported to v4.14
> kernel or later.
> ---
>   sound/core/control.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/control.c b/sound/core/control.c
> index 3fa1171dc1c2..49f3428dfacb 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -1398,8 +1398,9 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag,
>   	if (kctl->tlv.c == NULL)
>   		return -ENXIO;
>   
> -	/* When locked, this is unavailable. */
> -	if (vd->owner != NULL && vd->owner != file)
> +	// Write and command operations are not allowed for locked element.
> +	if (op_flag != SNDRV_CTL_TLV_OP_READ &&
> +	    vd->owner != NULL && vd->owner != file)
>   		return -EPERM;
>   
>   	return kctl->tlv.c(kctl, op_flag, size, buf);
> 

Thanks. Good catch. I would change only the comment back to /* */ to be
consistent with the other sound/core code.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>


-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
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