netdev - Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

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Message-ID: <ecc825e6-89d3-bbd5-5243-5cc66fa93045@oracle.com>
Date:   Thu, 14 Mar 2019 11:02:12 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, jgross@...e.com,
        sstabellini@...nel.org, davem@...emloft.net
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>
Subject: Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

On 3/14/19 10:52 AM, Oleksandr Andrushchenko wrote:
> On 3/14/19 4:47 PM, Boris Ostrovsky wrote:
>> On 3/14/19 9:17 AM, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
>>>
>>> Currently on driver resume we remove all the network queues and
>>> destroy shared Tx/Rx rings leaving the driver in its current state
>>> and never signaling the backend of this frontend's state change.
>>> This leads to the number of consequences:
>>> - when frontend withdraws granted references to the rings etc. it
>>> cannot
>>>    be cleanly done as the backend still holds those (it was not told to
>>>    free the resources)
>>> - it is not possible to resume driver operation as all the
>>> communication
>>>    means with the backned were destroyed by the frontend, thus
>>>    making the frontend appear to the guest OS as functional, but
>>>    not really.
>>
>> What do you mean? Are you saying that after resume you lose
>> connectivity?
> Exactly, if you take a look at the .resume callback as it is now
> what it does it destroys the rings etc. and never notifies the backend
> of that, e.g. it stays in, say, connected state with communication
> channels destroyed. It never goes into any other Xen bus state, so
> there is
> no way its state machine can help recovering.


My tree is about a month old so perhaps there is some sort of regression
but this certainly works for me. After resume netfront gets
XenbusStateInitWait from backend which causes xennet_connect().

-boris