[PATCH] ucm: Allow empty strings in "${var:...}" substitutions

[Pierre-Louis Bossart]

On 6/27/20 1:30 PM, Hans de Goede wrote:
> Recent ucm-conf changes introduce checks like this one in various places:
> 
> If.mspk {
>          Condition {
>                  Type String
>                  Empty "${var:MonoSpeaker}"
>          }
>          True ...
>          False ...
> }
> 
> The 'Empty "${var:MonoSpeaker}"' part can only every succeed if we do:
> 
> Define.MonoSpeaker ""
> 
> But so far that would result in an error like this one:
> 
> ALSA lib ucm_subs.c:367:(uc_mgr_get_substituted_value) variable '${var:MonoSpeaker}' is not defined in this context!
> ALSA lib main.c:983:(snd_use_case_mgr_open) error: failed to import cht-bsw-rt5672 use case configuration -22
> alsaucm: error failed to open sound card cht-bsw-rt5672: Invalid argument
> 
> This commit fixes this by allowing empty values for "${var:...}"
> substitutions.
> 
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
> Note besides the mentioned error, this also fixes similar errors I have
> been seeing on every board since alsa-ucm-conf commit d001c8de287f
> ("ucm.conf: add support for the kernel module name tree")

Well this is quite timely, I had to revert to older versions of UCM 
earlier today because of similar issues:

root at Zotac:~/alsa-lib# alsaucm -c SOF set _verb HiFi set _enadev Headphones
ALSA lib ucm_subs.c:367:(uc_mgr_get_substituted_value) variable 
'${var:V1}' is not defined in this context!
ALSA lib main.c:983:(snd_use_case_mgr_open) error: failed to import SOF 
use case configuration -22
alsaucm: error failed to open sound card SOF: Invalid argument

This error is gone with this patch + latest alsa-ucm-conf, so

Tested-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>

Thanks Hans!

> ---
>   src/ucm/ucm_subs.c | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/src/ucm/ucm_subs.c b/src/ucm/ucm_subs.c
> index 293426f2..a154aa51 100644
> --- a/src/ucm/ucm_subs.c
> +++ b/src/ucm/ucm_subs.c
> @@ -262,9 +262,10 @@ static char *rval_var(snd_use_case_mgr_t *uc_mgr, const char *id)
>   		goto __rval;						\
>   	}
>   
> -#define MATCH_VARIABLE2(name, id, fcn)					\
> +#define MATCH_VARIABLE2(name, id, fcn, empty_ok)			\
>   	if (strncmp((name), (id), sizeof(id) - 1) == 0) {		\
>   		idsize = sizeof(id) - 1;				\
> +		allow_empty = (empty_ok);				\
>   		fcn2 = (fcn);						\
>   		goto __match2;						\
>   	}
> @@ -314,11 +315,11 @@ __std:
>   		MATCH_VARIABLE(value, "${CardName}", rval_card_name, false);
>   		MATCH_VARIABLE(value, "${CardLongName}", rval_card_longname, false);
>   		MATCH_VARIABLE(value, "${CardComponents}", rval_card_components, true);
> -		MATCH_VARIABLE2(value, "${env:", rval_env);
> -		MATCH_VARIABLE2(value, "${sys:", rval_sysfs);
> -		MATCH_VARIABLE2(value, "${var:", rval_var);
> -		MATCH_VARIABLE2(value, "${CardNumberByName:", rval_card_number_by_name);
> -		MATCH_VARIABLE2(value, "${CardIdByName:", rval_card_id_by_name);
> +		MATCH_VARIABLE2(value, "${env:", rval_env, false);
> +		MATCH_VARIABLE2(value, "${sys:", rval_sysfs, false);
> +		MATCH_VARIABLE2(value, "${var:", rval_var, true);
> +		MATCH_VARIABLE2(value, "${CardNumberByName:", rval_card_number_by_name, false);
> +		MATCH_VARIABLE2(value, "${CardIdByName:", rval_card_id_by_name, false);
>   __merr:
>   		err = -EINVAL;
>   		tmp = strchr(value, '}');
>