ALSA: xen: Convert to generic PCM copy ops

This patch converts the xen frontend driver code to use the new
unified PCM copy callback.  It's a straightforward conversion from
*_user() to *_iter() variants.

Note that copy_from/to_iter() returns the copied bytes, hence the
error condition is adjusted accordingly.

Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: xen-devel@lists.xenproject.org
Link: https://lore.kernel.org/r/20230815190136.8987-16-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/xen/xen_snd_front_alsa.c

@@ -602,56 +602,24 @@ static snd_pcm_uframes_t alsa_pointer(struct snd_pcm_substream *substream)
 	return (snd_pcm_uframes_t)atomic_read(&stream->hw_ptr);
 }
 
-static int alsa_pb_copy_user(struct snd_pcm_substream *substream,
-			     int channel, unsigned long pos, void __user *src,
-			     unsigned long count)
+static int alsa_pb_copy(struct snd_pcm_substream *substream,
+			int channel, unsigned long pos, struct iov_iter *src,
+			unsigned long count)
 {
 	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
 
 	if (unlikely(pos + count > stream->buffer_sz))
 		return -EINVAL;
 
-	if (copy_from_user(stream->buffer + pos, src, count))
+	if (copy_from_iter(stream->buffer + pos, count, src) != count)
 		return -EFAULT;
 
 	return xen_snd_front_stream_write(&stream->evt_pair->req, pos, count);
 }
 
-static int alsa_pb_copy_kernel(struct snd_pcm_substream *substream,
-			       int channel, unsigned long pos, void *src,
-			       unsigned long count)
-{
-	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
-
-	if (unlikely(pos + count > stream->buffer_sz))
-		return -EINVAL;
-
-	memcpy(stream->buffer + pos, src, count);
-
-	return xen_snd_front_stream_write(&stream->evt_pair->req, pos, count);
-}
-
-static int alsa_cap_copy_user(struct snd_pcm_substream *substream,
-			      int channel, unsigned long pos, void __user *dst,
-			      unsigned long count)
-{
-	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
-	int ret;
-
-	if (unlikely(pos + count > stream->buffer_sz))
-		return -EINVAL;
-
-	ret = xen_snd_front_stream_read(&stream->evt_pair->req, pos, count);
-	if (ret < 0)
-		return ret;
-
-	return copy_to_user(dst, stream->buffer + pos, count) ?
-		-EFAULT : 0;
-}
-
-static int alsa_cap_copy_kernel(struct snd_pcm_substream *substream,
-				int channel, unsigned long pos, void *dst,
-				unsigned long count)
+static int alsa_cap_copy(struct snd_pcm_substream *substream,
+			 int channel, unsigned long pos, struct iov_iter *dst,
+			 unsigned long count)
 {
 	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
 	int ret;
@@ -663,8 +631,8 @@ static int alsa_cap_copy_kernel(struct snd_pcm_substream *substream,
 	if (ret < 0)
 		return ret;
 
-	memcpy(dst, stream->buffer + pos, count);
-
+	if (copy_to_iter(stream->buffer + pos, count, dst) != count)
+		return -EFAULT;
 	return 0;
 }
 
@@ -697,8 +665,7 @@ static const struct snd_pcm_ops snd_drv_alsa_playback_ops = {
 	.prepare	= alsa_prepare,
 	.trigger	= alsa_trigger,
 	.pointer	= alsa_pointer,
-	.copy_user	= alsa_pb_copy_user,
-	.copy_kernel	= alsa_pb_copy_kernel,
+	.copy		= alsa_pb_copy,
 	.fill_silence	= alsa_pb_fill_silence,
 };
 
@@ -710,8 +677,7 @@ static const struct snd_pcm_ops snd_drv_alsa_capture_ops = {
 	.prepare	= alsa_prepare,
 	.trigger	= alsa_trigger,
 	.pointer	= alsa_pointer,
-	.copy_user	= alsa_cap_copy_user,
-	.copy_kernel	= alsa_cap_copy_kernel,
+	.copy		= alsa_cap_copy,
 };
 
 static int new_pcm_instance(struct xen_snd_front_card_info *card_info,