vhost: Distinguish errors in vhost_backend_init()

Instead of just returning 0/-1 and letting the caller make up a
meaningless error message, add an Error parameter to allow reporting the
real error and switch to 0/-errno so that different kind of errors can
be distinguished in the caller.

Specifically, in vhost-user, EPROTO is used for all errors that relate
to the connection itself, whereas other error codes are used for errors
relating to the content of the connection. This will allow us later to
automatically reconnect when the connection goes away, without ending up
in an endless loop if it's a permanent error in the configuration.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210609154658.350308-3-kwolf@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 21 insertions, 20 deletions

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index ee57abe..024cb20 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1856,7 +1856,8 @@ static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
     return 0;
 }
 
-static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
+static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
+                                   Error **errp)
 {
     uint64_t features, protocol_features, ram_slots;
     struct vhost_user *u;
@@ -1871,7 +1872,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
 
     err = vhost_user_get_features(dev, &features);
     if (err < 0) {
-        return err;
+        return -EPROTO;
     }
 
     if (virtio_has_feature(features, VHOST_USER_F_PROTOCOL_FEATURES)) {
@@ -1880,7 +1881,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
         err = vhost_user_get_u64(dev, VHOST_USER_GET_PROTOCOL_FEATURES,
                                  &protocol_features);
         if (err < 0) {
-            return err;
+            return -EPROTO;
         }
 
         dev->protocol_features =
@@ -1891,14 +1892,14 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
             dev->protocol_features &= ~(1ULL << VHOST_USER_PROTOCOL_F_CONFIG);
         } else if (!(protocol_features &
                     (1ULL << VHOST_USER_PROTOCOL_F_CONFIG))) {
-            error_report("Device expects VHOST_USER_PROTOCOL_F_CONFIG "
-                    "but backend does not support it.");
-            return -1;
+            error_setg(errp, "Device expects VHOST_USER_PROTOCOL_F_CONFIG "
+                       "but backend does not support it.");
+            return -EINVAL;
         }
 
         err = vhost_user_set_protocol_features(dev, dev->protocol_features);
         if (err < 0) {
-            return err;
+            return -EPROTO;
         }
 
         /* query the max queues we support if backend supports Multiple Queue */
@@ -1906,12 +1907,12 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
             err = vhost_user_get_u64(dev, VHOST_USER_GET_QUEUE_NUM,
                                      &dev->max_queues);
             if (err < 0) {
-                return err;
+                return -EPROTO;
             }
         }
         if (dev->num_queues && dev->max_queues < dev->num_queues) {
-            error_report("The maximum number of queues supported by the "
-                         "backend is %" PRIu64, dev->max_queues);
+            error_setg(errp, "The maximum number of queues supported by the "
+                       "backend is %" PRIu64, dev->max_queues);
             return -EINVAL;
         }
 
@@ -1920,9 +1921,9 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
                     VHOST_USER_PROTOCOL_F_SLAVE_REQ) &&
                  virtio_has_feature(dev->protocol_features,
                     VHOST_USER_PROTOCOL_F_REPLY_ACK))) {
-            error_report("IOMMU support requires reply-ack and "
-                         "slave-req protocol features.");
-            return -1;
+            error_setg(errp, "IOMMU support requires reply-ack and "
+                       "slave-req protocol features.");
+            return -EINVAL;
         }
 
         /* get max memory regions if backend supports configurable RAM slots */
@@ -1932,15 +1933,15 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
         } else {
             err = vhost_user_get_max_memslots(dev, &ram_slots);
             if (err < 0) {
-                return err;
+                return -EPROTO;
             }
 
             if (ram_slots < u->user->memory_slots) {
-                error_report("The backend specified a max ram slots limit "
-                             "of %" PRIu64", when the prior validated limit was %d. "
-                             "This limit should never decrease.", ram_slots,
-                             u->user->memory_slots);
-                return -1;
+                error_setg(errp, "The backend specified a max ram slots limit "
+                           "of %" PRIu64", when the prior validated limit was "
+                           "%d. This limit should never decrease.", ram_slots,
+                           u->user->memory_slots);
+                return -EINVAL;
             }
 
             u->user->memory_slots = MIN(ram_slots, VHOST_USER_MAX_RAM_SLOTS);
@@ -1958,7 +1959,7 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque)
     if (dev->vq_index == 0) {
         err = vhost_setup_slave_channel(dev);
         if (err < 0) {
-            return err;
+            return -EPROTO;
         }
     }