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

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Message-ID: <CAOJe8K0cB9govqjLO8wtpwz1FcY23x+ppL97pC7c8UKbbMMXYQ@mail.gmail.com>
Date:   Thu, 7 May 2020 14:30:34 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
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 5/7/20, Paul Durrant <xadimgnik@...il.com> wrote:
>> -----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).

I made a change to xdp-netfront to keep the state of XDP
and then just pass the saved state in talk_to_netback()

>
>   Paul
>
>