From 8ccfb4a31fbc16e01e93d7989019e04c69a6284d Mon Sep 17 00:00:00 2001
From: Liam Girdwood <lrg@ti.com>
Date: Wed, 16 Feb 2011 16:50:12 +0000
Subject: [PATCH] ALSA: pcm - reject calls to open backend PCMs (temporary)

This stops userspace opening backlemd PCMs.

TODO: rework for upstream.

Signed-off-by: Liam Girdwood <lrg@ti.com>
---
 sound/core/pcm_native.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index c6698efb44c..0e972485449 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2036,6 +2036,12 @@ int snd_pcm_open_substream(struct snd_pcm *pcm, int stream,
 		goto error;
 	}
 
+	if (substream->ops == NULL) {
+		snd_printd("cannot open back end PCMs directly\n");
+		err = -ENODEV;
+		goto error;
+	}
+
 	if ((err = substream->ops->open(substream)) < 0)
 		goto error;