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Re: [Qemu-devel] [PATCH v2] vhost_net: don't enable vring if backend lac
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2] vhost_net: don't enable vring if backend lack this feature |
Date: |
Fri, 23 Sep 2016 18:33:47 +0300 |
On Fri, Sep 23, 2016 at 06:04:06PM +0800, Chen Hanxiao wrote:
> From: Chen Hanxiao <address@hidden>
>
> If backend(such as dpdk) lack the feather,
Sorry, I don't understand what does this mean.
> don't assume it in vring_enable.
> Or we may fail in vhost_net_start, then we can't use vhost.
> This will bring compat issue with old version backend.
>
> Signed-off-by: Chen Hanxiao <address@hidden>
> ---
> v2: return 0 there if protocol features aren't negotiated.
>
> 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..a1b796a 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);
> + /*
> + * Try to enable vring feature.
What does this mean?
> + * If protocol features aren't negotiated, return 0 for back compat.
How do you mean "for back compat"?
> + */
> + if (ret == 0) {
> + nc->vring_enable = enable;
> + }
> }
This clearly does not set vring_enable if vhost_set_vring_enable is
NULL.
>
> return 0;
> --
> 1.8.3.1
>