casaroli commented on code in PR #21408:
URL: https://github.com/apache/nuttx/pull/21408#discussion_r4473591572
##########
drivers/virtio/virtio-rng.c:
##########
@@ -160,23 +161,34 @@ static ssize_t virtio_rng_read(FAR struct file *filep,
FAR char *buffer,
cookie.len = 0;
nxsem_init(&cookie.sem, 0, 0);
+ /* Map the user buffer so the device side can access it. On MMIO/PCI
+ * map returns the buffer itself and the device writes the entropy straight
+ * into it (zero copy); a transport that cannot reach it (rptun, or a user
+ * buffer with CONFIG_ARCH_ADDRENV) bounces it and unmap copies the result
+ * back below.
+ */
+
+ ret = virtio_map_buf(priv->vdev, buffer, buflen, VIRTIO_DMA_FROM_DEVICE,
+ &mapped);
+ if (ret < 0)
+ {
+ return ret;
+ }
+
/* Add the input buffer to the virtqueue, and the cookie as the virtqueue
* cookie. (virtqueue_get_buffer() will return cookie).
*/
vb.len = buflen;
- vb.buf = virtio_zalloc_buf(priv->vdev, buflen, 16);
- if (vb.buf == NULL)
- {
- return -ENOMEM;
- }
+ vb.buf = mapped;
flags = spin_lock_irqsave(&priv->lock);
ret = virtqueue_add_buffer(vq, &vb, 0, 1, &cookie);
if (ret < 0)
{
spin_unlock_irqrestore(&priv->lock, flags);
- virtio_free_buf(priv->vdev, vb.buf);
+ virtio_unmap_buf(priv->vdev, buffer, buflen, VIRTIO_DMA_FROM_DEVICE,
Review Comment:
When `virtqueue_add_buffer()` fails, this unmap copies `buflen` bytes of a
`kmm_malloc()` bounce that the device never wrote into the caller's buffer;
virtio-blk now passes 0 on failure, and master frees the buffer here with no
copy.
Fix: pass 0 instead of `buflen`.
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