[Qemu-devel] [PATCH resend] vhost_net: don't enable vring if backend lack this feature

[Qemu-devel] [PATCH resend] vhost_net: don't enable vring if backend lack this feature

[Chen Hanxiao]

From: Chen Hanxiao <chenhanxiao@gmail.com>

If backend(such as dpdk) lack this feature,
don't assume it and mark it in vring_enable.
Or we may fail in vhost_net_start,
then we can't use vhost net.
This will bring compat issue with old version backend.

Signed-off-by: Chen Hanxiao <chenhanxiao@gmail.com>
---
 hw/net/vhost_net.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index f2d49ad..3819e65 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -425,11 +425,17 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
 {
     VHostNetState *net = get_vhost_net(nc);
     const VhostOps *vhost_ops = net->dev.vhost_ops;
-
-    nc->vring_enable = enable;
+    int ret;
 
     if (vhost_ops && vhost_ops->vhost_set_vring_enable) {
-        return vhost_ops->vhost_set_vring_enable(&net->dev, enable);
+        ret = vhost_ops->vhost_set_vring_enable(&net->dev, enable);
+        if (ret == 0) {
+            nc->vring_enable = enable;
+        } else {
+            nc->vring_enable = false;
+        }
+
+        return ret;
     }
 
     return 0;
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH resend] vhost_net: don't enable vring if backend lack this feature

[Michael S. Tsirkin]

On Tue, Sep 13, 2016 at 05:28:55PM +0800, Chen Hanxiao wrote:
> From: Chen Hanxiao <chenhanxiao@gmail.com>
> 
> If backend(such as dpdk) lack this feature,
> don't assume it and mark it in vring_enable.
> Or we may fail in vhost_net_start,
> then we can't use vhost net.
> This will bring compat issue with old version backend.
> 
> Signed-off-by: Chen Hanxiao <chenhanxiao@gmail.com>

Is there value in returning an error from vhost_user_set_vring_enable then?
Maybe we should just return 0 there if protocol
features aren't negotiated, or even change it to return void.


> ---
>  hw/net/vhost_net.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index f2d49ad..3819e65 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -425,11 +425,17 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
>  {
>      VHostNetState *net = get_vhost_net(nc);
>      const VhostOps *vhost_ops = net->dev.vhost_ops;
> -
> -    nc->vring_enable = enable;
> +    int ret;
>  
>      if (vhost_ops && vhost_ops->vhost_set_vring_enable) {
> -        return vhost_ops->vhost_set_vring_enable(&net->dev, enable);
> +        ret = vhost_ops->vhost_set_vring_enable(&net->dev, enable);
> +        if (ret == 0) {
> +            nc->vring_enable = enable;
> +        } else {
> +            nc->vring_enable = false;
> +        }
> +
> +        return ret;
>      }
>  
>      return 0;
> -- 
> 1.8.3.1
>