ALSA: pcm: Remove set_fs() in PCM core code

PCM core code has a few usages of set_fs(), mostly for two codepaths:
- The DELAY ioctl call from pcm_compat.c
- The ioctl wrapper in kernel context for PCM OSS and other

This patch removes the set_fs() usage in these places by a slight code
refactoring.  For the former point, snd_pcm_delay() is changed to
return the  value directly instead of putting the value to the given
address.  Each caller stores the result in an appropriate manner.

For fixing the latter, snd_pcm_lib_kernel_ioctl() is changed to call
the functions directly as well.  For achieving it, now the function
accepts only the limited set of ioctls that have been used, so far.
The primary user of this function is the PCM OSS layer, and the only
other user is USB UAC1 gadget driver.  Both drivers don't need the
full set of ioctls.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_compat.c

@@ -27,17 +27,13 @@ static int snd_pcm_ioctl_delay_compat(struct snd_pcm_substream *substream,
 				      s32 __user *src)
 {
 	snd_pcm_sframes_t delay;
-	mm_segment_t fs;
-	int err;
 
-	fs = snd_enter_user();
-	err = snd_pcm_delay(substream, &delay);
-	snd_leave_user(fs);
-	if (err < 0)
-		return err;
+	delay = snd_pcm_delay(substream);
+	if (delay < 0)
+		return delay;
 	if (put_user(delay, src))
 		return -EFAULT;
-	return err;
+	return 0;
 }
 
 static int snd_pcm_ioctl_rewind_compat(struct snd_pcm_substream *substream,

sound/core/pcm_native.c

@@ -181,20 +181,6 @@ void snd_pcm_stream_unlock_irqrestore(struct snd_pcm_substream *substream,
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_unlock_irqrestore);
 
-static inline mm_segment_t snd_enter_user(void)
-{
-	mm_segment_t fs = get_fs();
-	set_fs(get_ds());
-	return fs;
-}
-
-static inline void snd_leave_user(mm_segment_t fs)
-{
-	set_fs(fs);
-}
-
-
-
 int snd_pcm_info(struct snd_pcm_substream *substream, struct snd_pcm_info *info)
 {
 	struct snd_pcm_runtime *runtime;
@@ -1081,13 +1067,21 @@ static const struct action_ops snd_pcm_action_start = {
  * @substream: the PCM substream instance
  *
  * Return: Zero if successful, or a negative error code.
+ * The stream lock must be acquired before calling this function.
  */
 int snd_pcm_start(struct snd_pcm_substream *substream)
 {
 	return snd_pcm_action(&snd_pcm_action_start, substream,
 			      SNDRV_PCM_STATE_RUNNING);
 }
 
+/* take the stream lock and start the streams */
+static int snd_pcm_start_lock_irq(struct snd_pcm_substream *substream)
+{
+	return snd_pcm_action_lock_irq(&snd_pcm_action_start, substream,
+				       SNDRV_PCM_STATE_RUNNING);
+}
+
 /*
  * stop callbacks
  */
@@ -2575,8 +2569,7 @@ static int snd_pcm_hwsync(struct snd_pcm_substream *substream)
 	return err;
 }
 
-static int snd_pcm_delay(struct snd_pcm_substream *substream,
-			 snd_pcm_sframes_t __user *res)
+static snd_pcm_sframes_t snd_pcm_delay(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	int err;
@@ -2592,10 +2585,7 @@ static int snd_pcm_delay(struct snd_pcm_substream *substream,
 		n += runtime->delay;
 	}
 	snd_pcm_stream_unlock_irq(substream);
-	if (!err)
-		if (put_user(n, res))
-			err = -EFAULT;
-	return err;
+	return err < 0 ? err : n;
 }
 
 static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
@@ -2683,7 +2673,7 @@ static int snd_pcm_common_ioctl1(struct file *file,
 	case SNDRV_PCM_IOCTL_RESET:
 		return snd_pcm_reset(substream);
 	case SNDRV_PCM_IOCTL_START:
-		return snd_pcm_action_lock_irq(&snd_pcm_action_start, substream, SNDRV_PCM_STATE_RUNNING);
+		return snd_pcm_start_lock_irq(substream);
 	case SNDRV_PCM_IOCTL_LINK:
 		return snd_pcm_link(substream, (int)(unsigned long) arg);
 	case SNDRV_PCM_IOCTL_UNLINK:
@@ -2695,7 +2685,16 @@ static int snd_pcm_common_ioctl1(struct file *file,
 	case SNDRV_PCM_IOCTL_HWSYNC:
 		return snd_pcm_hwsync(substream);
 	case SNDRV_PCM_IOCTL_DELAY:
-		return snd_pcm_delay(substream, arg);
+	{
+		snd_pcm_sframes_t delay = snd_pcm_delay(substream);
+		snd_pcm_sframes_t __user *res = arg;
+
+		if (delay < 0)
+			return delay;
+		if (put_user(delay, res))
+			return -EFAULT;
+		return 0;
+	}
 	case SNDRV_PCM_IOCTL_SYNC_PTR:
 		return snd_pcm_sync_ptr(substream, arg);
 #ifdef CONFIG_SND_SUPPORT_OLD_API
@@ -2909,30 +2908,55 @@ static long snd_pcm_capture_ioctl(struct file *file, unsigned int cmd,
 				      (void __user *)arg);
 }
 
+/**
+ * snd_pcm_kernel_ioctl - Execute PCM ioctl in the kernel-space
+ * @substream: PCM substream
+ * @cmd: IOCTL cmd
+ * @arg: IOCTL argument
+ *
+ * The function is provided primarily for OSS layer and USB gadget drivers,
+ * and it allows only the limited set of ioctls (hw_params, sw_params,
+ * prepare, start, drain, drop, forward).
+ */
 int snd_pcm_kernel_ioctl(struct snd_pcm_substream *substream,
 			 unsigned int cmd, void *arg)
 {
-	mm_segment_t fs;
-	int result;
+	snd_pcm_uframes_t *frames = arg;
+	snd_pcm_sframes_t result;
 
-	fs = snd_enter_user();
-	switch (substream->stream) {
-	case SNDRV_PCM_STREAM_PLAYBACK:
-		result = snd_pcm_playback_ioctl1(NULL, substream, cmd,
-						 (void __user *)arg);
-		break;
-	case SNDRV_PCM_STREAM_CAPTURE:
-		result = snd_pcm_capture_ioctl1(NULL, substream, cmd,
-						(void __user *)arg);
-		break;
+	switch (cmd) {
+	case SNDRV_PCM_IOCTL_FORWARD:
+	{
+		/* provided only for OSS; capture-only and no value returned */
+		if (substream->stream != SNDRV_PCM_STREAM_CAPTURE)
+			return -EINVAL;
+		result = snd_pcm_capture_forward(substream, *frames);
+		return result < 0 ? result : 0;
+	}
+	case SNDRV_PCM_IOCTL_HW_PARAMS:
+		return snd_pcm_hw_params(substream, arg);
+	case SNDRV_PCM_IOCTL_SW_PARAMS:
+		return snd_pcm_sw_params(substream, arg);
+	case SNDRV_PCM_IOCTL_PREPARE:
+		return snd_pcm_prepare(substream, NULL);
+	case SNDRV_PCM_IOCTL_START:
+		return snd_pcm_start_lock_irq(substream);
+	case SNDRV_PCM_IOCTL_DRAIN:
+		return snd_pcm_drain(substream, NULL);
+	case SNDRV_PCM_IOCTL_DROP:
+		return snd_pcm_drop(substream);
+	case SNDRV_PCM_IOCTL_DELAY:
+	{
+		result = snd_pcm_delay(substream);
+		if (result < 0)
+			return result;
+		*frames = result;
+		return 0;
+	}
 	default:
-		result = -EINVAL;
-		break;
+		return -EINVAL;
 	}
-	snd_leave_user(fs);
-	return result;
 }
-
 EXPORT_SYMBOL(snd_pcm_kernel_ioctl);
 
 static ssize_t snd_pcm_read(struct file *file, char __user *buf, size_t count,