Re: [Qemu-devel] [PATCH v3 10/28] vhost: change some assert() for error_report() or silent fail

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 06, 2016 at 08:47:03PM +0200, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> Calling a vhost operation may fail, especially with disconnectable
> backends. Treat some that look harmless as recoverable errors (print
> error, or ignore on error code path).
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

These might be recoverable for vhost-user not for vhost_net.

IMO the backend should return 0 if error is benign,
report errors to vhost only if they are fatal.

For example, consider set mem table. Write failing is one thing,
and it's benign, but e.g. table too big is another thing and isn't.

Also, we might want to distinguish between EBADF (fd closed)
and other types of errors. All this knowledge belomgs in vhost user.

> ---
>  hw/virtio/vhost.c | 32 +++++++++++++++++++++-----------
>  1 file changed, 21 insertions(+), 11 deletions(-)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 75bc51e..e03a031 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -400,7 +400,10 @@ static inline void vhost_dev_log_resize(struct vhost_dev *dev, uint64_t size)
>      /* inform backend of log switching, this must be done before
>         releasing the current log, to ensure no logging is lost */
>      r = dev->vhost_ops->vhost_set_log_base(dev, log_base, log);
> -    assert(r >= 0);
> +    if (r < 0) {
> +        error_report("Failed to change backend log");
> +    }
> +
>      vhost_log_put(dev, true);
>      dev->log = log;
>      dev->log_size = size;
> @@ -567,7 +570,9 @@ static void vhost_commit(MemoryListener *listener)
>  
>      if (!dev->log_enabled) {
>          r = dev->vhost_ops->vhost_set_mem_table(dev, dev->mem);
> -        assert(r >= 0);
> +        if (r < 0) {
> +            error_report("Failed to set mem table");
> +        }
>          dev->memory_changed = false;
>          return;
>      }
> @@ -580,7 +585,9 @@ static void vhost_commit(MemoryListener *listener)
>          vhost_dev_log_resize(dev, log_size + VHOST_LOG_BUFFER);
>      }
>      r = dev->vhost_ops->vhost_set_mem_table(dev, dev->mem);
> -    assert(r >= 0);
> +    if (r < 0) {
> +        error_report("Failed to set mem table");
> +    }
>      /* To log less, can only decrease log size after table update. */
>      if (dev->log_size > log_size + VHOST_LOG_BUFFER) {
>          vhost_dev_log_resize(dev, log_size);
> @@ -649,6 +656,7 @@ static int vhost_virtqueue_set_addr(struct vhost_dev *dev,
>      };
>      int r = dev->vhost_ops->vhost_set_vring_addr(dev, &addr);
>      if (r < 0) {
> +        error_report("Failed to set vring addr");
>          return -errno;
>      }
>      return 0;
> @@ -662,12 +670,15 @@ static int vhost_dev_set_features(struct vhost_dev *dev, bool enable_log)
>          features |= 0x1ULL << VHOST_F_LOG_ALL;
>      }
>      r = dev->vhost_ops->vhost_set_features(dev, features);
> +    if (r < 0) {
> +        error_report("Failed to set features");
> +    }
>      return r < 0 ? -errno : 0;
>  }
>  
>  static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log)
>  {
> -    int r, t, i, idx;
> +    int r, i, idx;
>      r = vhost_dev_set_features(dev, enable_log);
>      if (r < 0) {
>          goto err_features;
> @@ -684,12 +695,10 @@ static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log)
>  err_vq:
>      for (; i >= 0; --i) {
>          idx = dev->vhost_ops->vhost_get_vq_index(dev, dev->vq_index + i);
> -        t = vhost_virtqueue_set_addr(dev, dev->vqs + i, idx,
> -                                     dev->log_enabled);
> -        assert(t >= 0);
> +        vhost_virtqueue_set_addr(dev, dev->vqs + i, idx,
> +                                 dev->log_enabled);
>      }
> -    t = vhost_dev_set_features(dev, dev->log_enabled);
> -    assert(t >= 0);
> +    vhost_dev_set_features(dev, dev->log_enabled);
>  err_features:
>      return r;
>  }
> @@ -937,7 +946,6 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
>          }
>      }
>  
> -    assert (r >= 0);
>      cpu_physical_memory_unmap(vq->ring, virtio_queue_get_ring_size(vdev, idx),
>                                0, virtio_queue_get_ring_size(vdev, idx));
>      cpu_physical_memory_unmap(vq->used, virtio_queue_get_used_size(vdev, idx),
> @@ -1191,7 +1199,9 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
>  
>      file.index = hdev->vhost_ops->vhost_get_vq_index(hdev, n);
>      r = hdev->vhost_ops->vhost_set_vring_call(hdev, &file);
> -    assert(r >= 0);
> +    if (r < 0) {
> +        error_report("Failed to set vring call");
> +    }
>  }
>  
>  uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
> -- 
> 2.9.0