netdev - RE: [PATCH net-next v7 2/2] xen networking: add XDP offset adjustment to xen-netback

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Date:   Thu, 7 May 2020 08:18:44 +0100
From:   Paul Durrant <xadimgnik@...il.com>
To:     "'Denis Kirjanov'" <kda@...ux-powerpc.org>
Cc:     <netdev@...r.kernel.org>, <jgross@...e.com>, <wei.liu@...nel.org>,
        <ilias.apalodimas@...aro.org>
Subject: RE: [PATCH net-next v7 2/2] xen networking: add XDP offset adjustment to xen-netback

> -----Original Message-----
> From: Denis Kirjanov <kda@...ux-powerpc.org>
> Sent: 06 May 2020 18:45
> To: paul@....org
> Cc: netdev@...r.kernel.org; jgross@...e.com; wei.liu@...nel.org; ilias.apalodimas@...aro.org
> Subject: Re: [PATCH net-next v7 2/2] xen networking: add XDP offset adjustment to xen-netback
> 
> On 5/5/20, Paul Durrant <xadimgnik@...il.com> wrote:
> >> -----Original Message-----
> >> >> @@ -417,6 +431,11 @@ static void frontend_changed(struct xenbus_device
> >> >> *dev,
> >> >>  		set_backend_state(be, XenbusStateConnected);
> >> >>  		break;
> >> >>
> >> >> +	case XenbusStateReconfiguring:
> >> >> +		read_xenbus_frontend_xdp(be, dev);
> >> >
> >> > Is the frontend always expected to trigger a re-configure, or could
> >> > feature-xdp already be enabled prior to connection?
> >>
> >> Yes, feature-xdp is set by the frontend when  xdp code is loaded.
> >>
> >
> > That's still ambiguous... what I'm getting at is whether you also need to
> > read the xdp state when transitioning into Connected as well as
> > Reconfiguring?
> 
> I have to read the state only during the Reconfiguring state since
> that's where an XDP program is loaded / unloaded and then we transition
> from Reconfigred to Connected
> 

Ok, but what about netback re-connection? It is possible that netback can be disconnected, unloaded, reloaded and re-attached to a running frontend. In this case XDP would be active so I still think read_xenbus_frontend_xdp() needs to form part of ring connection (if only in this case).

  Paul