netdev - Re: [PATCH 5/8] xen/netfront: read response from backend only once

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Date:   Mon, 17 May 2021 16:24:45 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] xen/netfront: read response from backend only once

On 17.05.21 16:20, Jan Beulich wrote:
> On 13.05.2021 12:02, Juergen Gross wrote:
>> In order to avoid problems in case the backend is modifying a response
>> on the ring page while the frontend has already seen it, just read the
>> response into a local buffer in one go and then operate on that buffer
>> only.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@...e.com>
> with one remark:
> 
>> @@ -830,24 +830,22 @@ static int xennet_get_extras(struct netfront_queue *queue,
>>   			break;
>>   		}
>>   
>> -		extra = (struct xen_netif_extra_info *)
>> -			RING_GET_RESPONSE(&queue->rx, ++cons);
>> +		RING_COPY_RESPONSE(&queue->rx, ++cons, &extra);
>>   
>> -		if (unlikely(!extra->type ||
>> -			     extra->type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
>> +		if (unlikely(!extra.type ||
>> +			     extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
>>   			if (net_ratelimit())
>>   				dev_warn(dev, "Invalid extra type: %d\n",
>> -					extra->type);
>> +					extra.type);
>>   			err = -EINVAL;
>>   		} else {
>> -			memcpy(&extras[extra->type - 1], extra,
>> -			       sizeof(*extra));
>> +			memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
> 
> Maybe take the opportunity and switch to (type safe) structure
> assignment?

Yes, good idea.


Juergen

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