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Subject: Re: [PATCH 5/8] xen/netfront: read response from backend only once
To:     Jan Beulich <jbeulich@suse.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        xen-devel@lists.xenproject.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210513100302.22027-1-jgross@suse.com>
 <20210513100302.22027-6-jgross@suse.com>
 <c9f90370-fc02-3f05-0670-35f795c59d95@suse.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <132c33ae-52c9-532b-b0b4-b5952db09720@suse.com>
Date:   Mon, 17 May 2021 16:24:45 +0200
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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>,
 "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>,
 xen-devel@lists.xenproject.org, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org
Message-ID: <132c33ae-52c9-532b-b0b4-b5952db09720@suse.com>
Subject: Re: [PATCH 5/8] xen/netfront: read response from backend only once
References: <20210513100302.22027-1-jgross@suse.com>
 <20210513100302.22027-6-jgross@suse.com>
 <c9f90370-fc02-3f05-0670-35f795c59d95@suse.com>
In-Reply-To: <c9f90370-fc02-3f05-0670-35f795c59d95@suse.com>

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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@suse.com>
>=20
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> with one remark:
>=20
>> @@ -830,24 +830,22 @@ static int xennet_get_extras(struct netfront_que=
ue *queue,
>>   			break;
>>   		}
>>  =20
>> -		extra =3D (struct xen_netif_extra_info *)
>> -			RING_GET_RESPONSE(&queue->rx, ++cons);
>> +		RING_COPY_RESPONSE(&queue->rx, ++cons, &extra);
>>  =20
>> -		if (unlikely(!extra->type ||
>> -			     extra->type >=3D XEN_NETIF_EXTRA_TYPE_MAX)) {
>> +		if (unlikely(!extra.type ||
>> +			     extra.type >=3D XEN_NETIF_EXTRA_TYPE_MAX)) {
>>   			if (net_ratelimit())
>>   				dev_warn(dev, "Invalid extra type: %d\n",
>> -					extra->type);
>> +					extra.type);
>>   			err =3D -EINVAL;
>>   		} else {
>> -			memcpy(&extras[extra->type - 1], extra,
>> -			       sizeof(*extra));
>> +			memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
>=20
> Maybe take the opportunity and switch to (type safe) structure
> assignment?

Yes, good idea.


Juergen

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