netdev - Re: [GIT/PATCH v4] xen network backend driver

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Message-ID: <AANLkTinHyFLRkeb60x4Q6uUw6p43XBjk5rpqCMo49WKF@mail.gmail.com>
Date:	Thu, 10 Mar 2011 18:33:05 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: Re: [GIT/PATCH v4] xen network backend driver

2011/3/10 Ian Campbell <Ian.Campbell@...rix.com>:
> The following patch is the fourth iteration of the Xen network backend
> driver for upstream Linux.
>
> This driver ("netback") is the host side counterpart to the frontend
> driver in drivers/net/xen-netfront.c. The PV protocol is also
> implemented by frontend drivers in other OSes too, such as the BSDs and
> even Windows.
[...]
> --- /dev/null
> +++ b/drivers/net/xen-netback/common.h
> @@ -0,0 +1,162 @@
[...]
> +struct xenvif {
[...]
> +       /* Flags that must not be set in dev->features */
> +       int features_disabled;
> +
> +       /* Frontend feature information. */
> +       u8 can_sg:1;
> +       u8 gso:1;
> +       u8 gso_prefix:1;
> +       u8 csum:1;
[...]
> --- /dev/null
> +++ b/drivers/net/xen-netback/interface.c
> @@ -0,0 +1,424 @@
[...]
> +static int xenvif_change_mtu(struct net_device *dev, int mtu)
> +{
> +       struct xenvif *vif = netdev_priv(dev);
> +       int max = vif->can_sg ? 65535 - VLAN_ETH_HLEN : ETH_DATA_LEN;
> +
> +       if (mtu > max)
> +               return -EINVAL;
> +       dev->mtu = mtu;
> +       return 0;
> +}
> +
> +static void xenvif_set_features(struct xenvif *vif)
> +{
> +       struct net_device *dev = vif->dev;
> +       int features = dev->features;
> +
> +       if (vif->can_sg)
> +               features |= NETIF_F_SG;
> +       if (vif->gso || vif->gso_prefix)
> +               features |= NETIF_F_TSO;
> +       if (vif->csum)
> +               features |= NETIF_F_IP_CSUM;
> +
> +       features &= ~(vif->features_disabled);
> +
> +       if (!(features & NETIF_F_SG) && dev->mtu > ETH_DATA_LEN)
> +               dev->mtu = ETH_DATA_LEN;
> +
> +       dev->features = features;
> +}
> +
> +static int xenvif_set_tx_csum(struct net_device *dev, u32 data)
> +{
> +       struct xenvif *vif = netdev_priv(dev);
> +       if (data) {
> +               if (!vif->csum)
> +                       return -EOPNOTSUPP;
> +               vif->features_disabled &= ~NETIF_F_IP_CSUM;
> +       } else {
> +               vif->features_disabled |= NETIF_F_IP_CSUM;
> +       }
> +
> +       xenvif_set_features(vif);
> +       return 0;
> +}
> +
> +static int xenvif_set_sg(struct net_device *dev, u32 data)
> +{
> +       struct xenvif *vif = netdev_priv(dev);
> +       if (data) {
> +               if (!vif->can_sg)
> +                       return -EOPNOTSUPP;
> +               vif->features_disabled &= ~NETIF_F_SG;
> +       } else {
> +               vif->features_disabled |= NETIF_F_SG;
> +       }
> +
> +       xenvif_set_features(vif);
> +       return 0;
> +}
> +
> +static int xenvif_set_tso(struct net_device *dev, u32 data)
> +{
> +       struct xenvif *vif = netdev_priv(dev);
> +       if (data) {
> +               if (!vif->gso && !vif->gso_prefix)
> +                       return -EOPNOTSUPP;
> +               vif->features_disabled &= ~NETIF_F_TSO;
> +       } else {
> +               vif->features_disabled |= NETIF_F_TSO;
> +       }
> +
> +       xenvif_set_features(vif);
> +       return 0;
> +}
[...]

You could make this simpler by using netdev->hw_features and
ndo_fix_features/ndo_set_features calls recently introduced in
net-next. I'll reply with a proof-of-concept patch for xen-netfront.

Best Regards,
Michał Mirosław
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