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

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Date:   Thu, 14 Mar 2019 15:50:10 +0200
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, jgross@...e.com,
        boris.ostrovsky@...cle.com, sstabellini@...nel.org,
        davem@...emloft.net
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

I am still confused about suspend/resume for the front drivers,
for instance, block front [1] does implement full/proper reconnect
on .resume, but net front only does this partially.

Could anyone please shed some light on suspend/resume design?

Thank you,
Oleksandr

On 3/14/19 3:17 PM, 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.
>
> Fix this by not destroying communication channels/rings on driver
> resume.
>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> ---
>   drivers/net/xen-netfront.c | 17 -----------------
>   1 file changed, 17 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index c914c24f880b..2ca162048da4 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1422,22 +1422,6 @@ static void xennet_disconnect_backend(struct netfront_info *info)
>   	}
>   }
>   
> -/**
> - * We are reconnecting to the backend, due to a suspend/resume, or a backend
> - * driver restart.  We tear down our netif structure and recreate it, but
> - * leave the device-layer structures intact so that this is transparent to the
> - * rest of the kernel.
> - */
> -static int netfront_resume(struct xenbus_device *dev)
> -{
> -	struct netfront_info *info = dev_get_drvdata(&dev->dev);
> -
> -	dev_dbg(&dev->dev, "%s\n", dev->nodename);
> -
> -	xennet_disconnect_backend(info);
> -	return 0;
> -}
> -
>   static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
>   {
>   	char *s, *e, *macstr;
> @@ -2185,7 +2169,6 @@ static struct xenbus_driver netfront_driver = {
>   	.ids = netfront_ids,
>   	.probe = netfront_probe,
>   	.remove = xennet_remove,
> -	.resume = netfront_resume,
>   	.otherend_changed = netback_changed,
>   };
>   

[1] 
https://elixir.bootlin.com/linux/v5.0.2/source/drivers/block/xen-blkfront.c#L2072