pcm: another weird API abuse

readv() and writev() should _not_ ignore all but the first ->iov_len,
among other things.  Really weird abuse of those syscalls - it
expects a vector element per channel, with identical lengths (it
actually assumes them to be identical - no checking is done).
readv() and writev() are really bad match for that.  Unfortunately,
userland API is userland API and we can't do anything about them.

Converted to ->read_iter/->write_iter.  Please, _please_ don't do
anything of that kind when designing new interfaces.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

sound/core/pcm_native.c

@@ -3033,9 +3033,7 @@ static ssize_t snd_pcm_write(struct file *file, const char __user *buf,
 	return result;
 }
 
-static ssize_t snd_pcm_aio_read(struct kiocb *iocb, const struct iovec *iov,
-			     unsigned long nr_segs, loff_t pos)
-
+static ssize_t snd_pcm_readv(struct kiocb *iocb, struct iov_iter *to)
 {
 	struct snd_pcm_file *pcm_file;
 	struct snd_pcm_substream *substream;
@@ -3052,16 +3050,18 @@ static ssize_t snd_pcm_aio_read(struct kiocb *iocb, const struct iovec *iov,
 	runtime = substream->runtime;
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN)
 		return -EBADFD;
-	if (nr_segs > 1024 || nr_segs != runtime->channels)
+	if (!iter_is_iovec(to))
+		return -EINVAL;
+	if (to->nr_segs > 1024 || to->nr_segs != runtime->channels)
 		return -EINVAL;
-	if (!frame_aligned(runtime, iov->iov_len))
+	if (!frame_aligned(runtime, to->iov->iov_len))
 		return -EINVAL;
-	frames = bytes_to_samples(runtime, iov->iov_len);
-	bufs = kmalloc(sizeof(void *) * nr_segs, GFP_KERNEL);
+	frames = bytes_to_samples(runtime, to->iov->iov_len);
+	bufs = kmalloc(sizeof(void *) * to->nr_segs, GFP_KERNEL);
 	if (bufs == NULL)
 		return -ENOMEM;
-	for (i = 0; i < nr_segs; ++i)
-		bufs[i] = iov[i].iov_base;
+	for (i = 0; i < to->nr_segs; ++i)
+		bufs[i] = to->iov[i].iov_base;
 	result = snd_pcm_lib_readv(substream, bufs, frames);
 	if (result > 0)
 		result = frames_to_bytes(runtime, result);
@@ -3069,8 +3069,7 @@ static ssize_t snd_pcm_aio_read(struct kiocb *iocb, const struct iovec *iov,
 	return result;
 }
 
-static ssize_t snd_pcm_aio_write(struct kiocb *iocb, const struct iovec *iov,
-			      unsigned long nr_segs, loff_t pos)
+static ssize_t snd_pcm_writev(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct snd_pcm_file *pcm_file;
 	struct snd_pcm_substream *substream;
@@ -3087,15 +3086,17 @@ static ssize_t snd_pcm_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	runtime = substream->runtime;
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN)
 		return -EBADFD;
-	if (nr_segs > 128 || nr_segs != runtime->channels ||
-	    !frame_aligned(runtime, iov->iov_len))
+	if (!iter_is_iovec(from))
+		return -EINVAL;
+	if (from->nr_segs > 128 || from->nr_segs != runtime->channels ||
+	    !frame_aligned(runtime, from->iov->iov_len))
 		return -EINVAL;
-	frames = bytes_to_samples(runtime, iov->iov_len);
-	bufs = kmalloc(sizeof(void *) * nr_segs, GFP_KERNEL);
+	frames = bytes_to_samples(runtime, from->iov->iov_len);
+	bufs = kmalloc(sizeof(void *) * from->nr_segs, GFP_KERNEL);
 	if (bufs == NULL)
 		return -ENOMEM;
-	for (i = 0; i < nr_segs; ++i)
-		bufs[i] = iov[i].iov_base;
+	for (i = 0; i < from->nr_segs; ++i)
+		bufs[i] = from->iov[i].iov_base;
 	result = snd_pcm_lib_writev(substream, bufs, frames);
 	if (result > 0)
 		result = frames_to_bytes(runtime, result);
@@ -3633,7 +3634,7 @@ const struct file_operations snd_pcm_f_ops[2] = {
 	{
 		.owner =		THIS_MODULE,
 		.write =		snd_pcm_write,
-		.aio_write =		snd_pcm_aio_write,
+		.write_iter =		snd_pcm_writev,
 		.open =			snd_pcm_playback_open,
 		.release =		snd_pcm_release,
 		.llseek =		no_llseek,
@@ -3647,7 +3648,7 @@ const struct file_operations snd_pcm_f_ops[2] = {
 	{
 		.owner =		THIS_MODULE,
 		.read =			snd_pcm_read,
-		.aio_read =		snd_pcm_aio_read,
+		.read_iter =		snd_pcm_readv,
 		.open =			snd_pcm_capture_open,
 		.release =		snd_pcm_release,
 		.llseek =		no_llseek,