[RFC PATCH v3 19/20] hw/virtio: probe backend for specs if it supports it

["Alex Bennée" <alex.bennee@linaro.org>]

Now we have detected and validated the protocol support lets do the
probe. The empty state indicates no probe took place.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 include/hw/virtio/vhost.h | 12 +++++++
 hw/virtio/vhost-user.c    | 73 +++++++++++++++++++++++++++++++++++----
 hw/virtio/vhost.c         |  2 +-
 3 files changed, 79 insertions(+), 8 deletions(-)

diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 912706668a..1d8de1c558 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -68,6 +68,13 @@ typedef struct VhostDevConfigOps {
 
 struct vhost_memory;
 
+typedef struct VhostUserBackendSpecs {
+    uint32_t device_id;
+    uint32_t config_size;
+    uint32_t min_vqs;
+    uint32_t max_vqs;
+} VhostUserBackendSpecs;
+
 /**
  * struct vhost_dev - common vhost_dev structure
  * @vhost_ops: backend specific ops
@@ -107,11 +114,15 @@ struct vhost_dev {
      * VHOST_USER_SET_FEATURES or VHOST_NET_F_VIRTIO_NET_HDR. Its
      * future use should be discouraged and the variable retired as
      * its easy to confuse with the VirtIO backend_features.
+     *
+     * @specs: the results of a GET_BACKEND_SPECS probe.
      */
     uint64_t features;
     uint64_t acked_features;
     uint64_t backend_features;
 
+    VhostUserBackendSpecs specs;
+
     /**
      * @protocol_features: is the vhost-user only feature set by
      * VHOST_USER_SET_PROTOCOL_FEATURES. Protocol features are only
@@ -134,6 +145,7 @@ struct vhost_dev {
     QLIST_HEAD(, vhost_iommu) iommu_list;
     IOMMUNotifier n;
     const VhostDevConfigOps *config_ops;
+
 };
 
 extern const VhostOps kernel_ops;
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 3116b3e46a..36aa4ec2d5 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -123,6 +123,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_REM_MEM_REG = 38,
     VHOST_USER_SET_STATUS = 39,
     VHOST_USER_GET_STATUS = 40,
+    VHOST_USER_GET_BACKEND_SPECS = 41,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -204,13 +205,6 @@ typedef struct VhostUserInflight {
     uint16_t queue_size;
 } VhostUserInflight;
 
-typedef struct VhostUserBackendSpecs {
-    uint32_t device_id;
-    uint32_t config_size;
-    uint32_t min_vqs;
-    uint32_t max_vqs;
-} VhostUserBackendSpecs;
-
 typedef struct {
     VhostUserRequest request;
 
@@ -1991,6 +1985,56 @@ static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
     return 0;
 }
 
+static bool vhost_user_get_backend_specs(struct vhost_dev *dev, Error **errp)
+{
+    int ret;
+    VhostUserMsg msg = {
+        .hdr.request = VHOST_USER_GET_BACKEND_SPECS,
+        .hdr.flags = VHOST_USER_VERSION,
+        .hdr.size = VHOST_USER_HDR_SIZE,
+    };
+
+    if (!virtio_has_feature(dev->protocol_features,
+                VHOST_USER_PROTOCOL_F_STANDALONE)) {
+        error_setg(errp, "VHOST_USER_PROTOCOL_F_STANDALONE not supported");
+        return -EINVAL;
+    }
+
+    ret = vhost_user_write(dev, &msg, NULL, 0);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "vhost_get_backend send failed");
+        return ret;
+    }
+
+    ret = vhost_user_read(dev, &msg);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "vhost_get_backend recv failed");
+        return ret;
+    }
+
+    if (msg.hdr.request != VHOST_USER_GET_BACKEND_SPECS) {
+        error_setg(errp,
+                   "Received unexpected msg type. Expected %d received %d",
+                   VHOST_USER_GET_BACKEND_SPECS, msg.hdr.request);
+        return -EPROTO;
+    }
+
+    if (msg.hdr.size != sizeof(msg.payload.specs)) {
+        error_setg(errp, "Received bad msg size.");
+        return -EPROTO;
+    }
+
+    if (msg.payload.specs.config_size && !virtio_has_feature(dev->protocol_features,
+                                                             VHOST_USER_PROTOCOL_F_CONFIG)) {
+        error_setg(errp, "VHOST_USER_PROTOCOL_F_CONFIG not supported");
+        return -EPROTO;
+    }
+
+    dev->specs = msg.payload.specs;
+
+    return 0;
+}
+
 static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
                                    Error **errp)
 {
@@ -2073,6 +2117,21 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
             return -EPROTO;
         }
 
+        if (dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_STANDALONE)) {
+            err = vhost_user_get_backend_specs(dev, errp);
+            if (err < 0) {
+                error_setg_errno(errp, EPROTO, "vhost_get_backend_specs failed");
+                return -EPROTO;
+            }
+            /*
+             * If this was never set by the user we can now fill it in
+             * so we can continue the initialisation
+             */
+            if (!dev->nvqs) {
+                dev->nvqs = dev->specs.min_vqs;
+            }
+        }
+
         /* query the max queues we support if backend supports Multiple Queue */
         if (dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_MQ)) {
             err = vhost_user_get_u64(dev, VHOST_USER_GET_QUEUE_NUM,
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 4c73ced3b7..d14467aa1c 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1450,7 +1450,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
     }
 
     /* Skip if we don't yet have number of vqs */
-    if (hdev->vqs && hdev->nvqs) {
+    if (hdev->nvqs) {
         if (!vhost_init_virtqs(hdev, busyloop_timeout, errp)) {
             goto fail_busyloop;
         }
-- 
2.39.2