[alsa-devel] unable to create IPC shm instance; SND_PCM_DIRECT_MAGIC

I was wondering if anyone could explain the point of SND_PCM_DIRECT_MAGIC and dmix->shmptr->magic?

Specifically, what it's doing in pcm_direct.c from this commit? http://git.alsa-project.org/?p=alsa-lib.git;a=blobdiff;f=src/pcm/pcm_direct....

I am trying to use pcm_dmix.c, but this is occasionally failing

first_instance = ret = snd_pcm_direct_shm_create_or_connect(dmix); if (ret < 0) { SNDERR("unable to create IPC shm instance"); goto _err; }

because dmix->shmptr->magic is not correctly set to SND_PCM_DIRECT_MAGIC.

Thanks for any information!

-Mike