[PATCH - aconnect 1/1] Fix aconnect printing card and pid on older kernels

[PATCH - aconnect 1/1] Fix aconnect printing card and pid on older kernels

[Adam Goode]

alsa-lib is changed to return a distinct negative value if running on
an older kernel. -1 is only returned now if the kernel knows for sure
that there is no card or pid. On older kernels, alsa-lib will return
-ENOSYS.

Signed-off-by: Adam Goode <agoode@google.com>

diff --git a/seq/aconnect/aconnect.c b/seq/aconnect/aconnect.c
index 85a7770..bbc5bb3 100644
--- a/seq/aconnect/aconnect.c
+++ b/seq/aconnect/aconnect.c
@@ -177,13 +177,13 @@ static void print_port(snd_seq_t *seq, snd_seq_client_info_t *cinfo,
 #ifdef HAVE_SEQ_CLIENT_INFO_GET_CARD
 		card = snd_seq_client_info_get_card(cinfo);
 #endif
-		if (card != -1)
+		if (card >= 0)
 			printf(",card=%d", card);
 
 #ifdef HAVE_SEQ_CLIENT_INFO_GET_PID
 		pid = snd_seq_client_info_get_pid(cinfo);
 #endif
-		if (pid != -1)
+		if (pid >= 0)
 			printf(",pid=%d", pid);
 		printf("]\n");
 	}
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH - aconnect 1/1] Fix aconnect printing card and pid on older kernels

[Martin Koegler]

On Fri, Apr 01, 2016 at 01:35:01PM -0400, Adam Goode wrote:
> alsa-lib is changed to return a distinct negative value if running on
> an older kernel. -1 is only returned now if the kernel knows for sure
> that there is no card or pid. On older kernels, alsa-lib will return
> -ENOSYS.
> 

Shouldn't we also update the default values of card/pid to -ENOSYS to be more consistent:
                int card = -1, pid = -1;

> @@ -177,13 +177,13 @@ static void print_port(snd_seq_t *seq, snd_seq_client_info_t *cinfo,
>  #ifdef HAVE_SEQ_CLIENT_INFO_GET_CARD
>  		card = snd_seq_client_info_get_card(cinfo);
>  #endif
> -		if (card != -1)
> +		if (card >= 0)
>  			printf(",card=%d", card);

aconnect from alsa-utils 1.1.1 will break with alsa-lib containing your patch.

The new API is propably not yet widely used, so I think that a ABI change can still be possible.
But in that case, alsa-lib/alsa-utils 1.1.1 need quickly be replaced by new releases, so that people
don't start using the old API.

Regards,
Martin