vhost: do not assert() on vhost_ops failure

Calling a vhost operation may fail, for example with disconnected
vhost-user backend, but qemu shouldn't abort in this case.

Log an error instead, except on error and cleanup code paths where it
can be mostly ignored.

Let's use a VHOST_OPS_DEBUG macro to easily disable those messages once
disconnected backend stabilizes.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost.c

@@ -27,6 +27,18 @@
 #include "hw/virtio/virtio-access.h"
 #include "migration/migration.h"
 
+/* enabled until disconnected backend stabilizes */
+#define _VHOST_DEBUG 1
+
+#ifdef _VHOST_DEBUG
+#define VHOST_OPS_DEBUG(fmt, ...) \
+    do { error_report(fmt ": %s (%d)", ## __VA_ARGS__, \
+                      strerror(errno), errno); } while (0)
+#else
+#define VHOST_OPS_DEBUG(fmt, ...) \
+    do { } while (0)
+#endif
+
 static struct vhost_log *vhost_log;
 static struct vhost_log *vhost_log_shm;
 
@@ -400,7 +412,10 @@ 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) {
+        VHOST_OPS_DEBUG("vhost_set_log_base failed");
+    }
+
     vhost_log_put(dev, true);
     dev->log = log;
     dev->log_size = size;
@@ -567,7 +582,9 @@ 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) {
+            VHOST_OPS_DEBUG("vhost_set_mem_table failed");
+        }
         dev->memory_changed = false;
         return;
     }
@@ -580,7 +597,9 @@ 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) {
+        VHOST_OPS_DEBUG("vhost_set_mem_table failed");
+    }
     /* 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);
@@ -667,7 +686,7 @@ static int vhost_dev_set_features(struct vhost_dev *dev, bool enable_log)
 
 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 +703,10 @@ 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;
 }
@@ -929,15 +946,11 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
      * native as legacy devices expect so by default.
      */
     if (vhost_needs_vring_endian(vdev)) {
-        r = vhost_virtqueue_set_vring_endian_legacy(dev,
-                                                    !virtio_is_big_endian(vdev),
-                                                    vhost_vq_index);
-        if (r < 0) {
-            error_report("failed to reset vring endianness");
-        }
+        vhost_virtqueue_set_vring_endian_legacy(dev,
+                                                !virtio_is_big_endian(vdev),
+                                                vhost_vq_index);
     }
 
-    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),
@@ -1228,7 +1241,9 @@ 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) {
+        VHOST_OPS_DEBUG("vhost_set_vring_call failed");
+    }
 }
 
 uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,