typedef struct snd_mixer_callbacks
{
  void *private_data;		/* should be used with an application */
  void (*rebuild) (void *private_data);
  void (*element) (void *private_data, int cmd, snd_mixer_eid_t * eid);
  void (*group) (void *private_data, int cmd, snd_mixer_gid_t * gid);
  void *reserved[28];		/* reserved for the future use - must be NULL!!! */
}
snd_mixer_callbacks_t;

• int snd_mixer_read (snd_mixer_t * handle, snd_mixer_callbacks_t * callbacks);