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Tue, 28 Jul 2020 11:31:32 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CF65352051; Tue, 28 Jul 2020 11:31:31 +0000 (GMT) Received: from oc2783563651 (unknown [9.145.179.56]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 595085204E; Tue, 28 Jul 2020 11:31:31 +0000 (GMT) Date: Tue, 28 Jul 2020 13:31:29 +0200 From: Halil Pasic To: Cornelia Huck Subject: Re: [RFC v2 2/3] libvhost-user: handle endianness as mandated by the spec Message-ID: <20200728133129.386e2025.pasic@linux.ibm.com> In-Reply-To: <20200728124850.7c15eade.cohuck@redhat.com> References: <20200717092929.19453-1-mhartmay@linux.ibm.com> <20200717092929.19453-3-mhartmay@linux.ibm.com> <20200721093942-mutt-send-email-mst@kernel.org> <20200721184456.1305ca0b.pasic@linux.ibm.com> <20200728124850.7c15eade.cohuck@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-28_07:2020-07-28, 2020-07-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 priorityscore=1501 phishscore=0 spamscore=0 mlxscore=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=944 adultscore=0 clxscore=1015 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007280085 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pasic@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/28 07:31:36 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" , "Michael S. Tsirkin" , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Marc Hartmayer , Stefan Hajnoczi , =?UTF-8?B?TWFyYy1BbmRyw6k=?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 28 Jul 2020 12:48:50 +0200 Cornelia Huck wrote: > On Tue, 21 Jul 2020 18:44:56 +0200 > Halil Pasic wrote: > > > On Tue, 21 Jul 2020 09:40:10 -0400 > > "Michael S. Tsirkin" wrote: > > > > > On Fri, Jul 17, 2020 at 11:29:28AM +0200, Marc Hartmayer wrote: > > > > Since virtio existed even before it got standardized, the virtio > > > > standard defines the following types of virtio devices: > > > > > > > > + legacy device (pre-virtio 1.0) > > > > + non-legacy or VIRTIO 1.0 device > > > > + transitional device (which can act both as legacy and non-legacy) > > > > > > > > Virtio 1.0 defines the fields of the virtqueues as little endian, > > > > while legacy uses guest's native endian [1]. Currently libvhost-user > > > > does not handle virtio endianness at all, i.e. it works only if the > > > > native endianness matches with whatever is actually needed. That means > > > > things break spectacularly on big-endian targets. Let us handle virtio > > > > endianness for non-legacy as required by the virtio specification > > > > [1]. We will fence non-legacy virtio devices with the upcoming patch. > > > > > > > > [1] https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-210003 > > > > > > > > Signed-off-by: Marc Hartmayer > > > > > > > > --- > > > > Note: As we don't support legacy virtio devices > > > > > > Who's "we" in this sentence? vhost user supports legacy generally ... > > > > In that sentence "we" is the library "libvhost-user". I would like > > to avoid s390x being an oddball regarding this. Marc's previous > > version made an attempt at correct endianness handling for legacy > > and non-legacy. That spawned a discussion on how we don't want > > legacy devices in this context. This series makes what seemed to be the > > consensus reached in that discussion explicit: namely that libvhost-user > > does not support legacy-virtio. > > Can someone please clarify what libvhost-user actually supports? > > virtio-fs is clearly non-legacy only, but in the changelog I also see a > mention of scsi, and that one probably does support legacy? > > Can we make a distinction along the lines of: > - if we are non-legacy, we support any endianness; > - if we are legacy, we support little endian host/guest only? > I don't like the idea of this conditional support of legacy (with a condition being a little endian host/guest). The library is supposed to be portable in my opinion. Regards, Halil