oss_ioctl
int (*oss_ioctl)(struct snd_emux *emu, int cmd, int p1, int p2);
static int oss_ioctl(struct snd_emux *emu, int cmd, int p1, int p2);
.oss_ioctl = oss_ioctl,
if (emu->ops.oss_ioctl)
emu->ops.oss_ioctl(emu, cmd, p1, p2);