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[79.34.249.199]) by smtp.gmail.com with ESMTPSA id o15sm2891607wmh.39.2021.02.23.06.50.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 06:50:19 -0800 (PST) Date: Tue, 23 Feb 2021 15:50:16 +0100 From: Stefano Garzarella To: Arseny Krasnov Cc: Stefan Hajnoczi , "Michael S. Tsirkin" , Jason Wang , "David S. Miller" , Jakub Kicinski , Jorgen Hansen , Andra Paraschiv , Norbert Slusarek , Colin Ian King , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stsp2@yandex.ru, oxffffaa@gmail.com Subject: Re: [RFC PATCH v5 00/19] virtio/vsock: introduce SOCK_SEQPACKET support Message-ID: <20210223145016.ddavx6fihq4akdim@steredhat> References: <20210218053347.1066159-1-arseny.krasnov@kaspersky.com> <20210222142311.gekdd7gsm33wglos@steredhat> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20210222142311.gekdd7gsm33wglos@steredhat> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Feb 22, 2021 at 03:23:11PM +0100, Stefano Garzarella wrote: >Hi Arseny, > >On Thu, Feb 18, 2021 at 08:33:44AM +0300, Arseny Krasnov wrote: >> This patchset impelements support of SOCK_SEQPACKET for virtio >>transport. >> As SOCK_SEQPACKET guarantees to save record boundaries, so to >>do it, two new packet operations were added: first for start of record >>and second to mark end of record(SEQ_BEGIN and SEQ_END later). Also, >>both operations carries metadata - to maintain boundaries and payload >>integrity. Metadata is introduced by adding special header with two >>fields - message count and message length: >> >> struct virtio_vsock_seq_hdr { >> __le32 msg_cnt; >> __le32 msg_len; >> } __attribute__((packed)); >> >> This header is transmitted as payload of SEQ_BEGIN and SEQ_END >>packets(buffer of second virtio descriptor in chain) in the same way as >>data transmitted in RW packets. Payload was chosen as buffer for this >>header to avoid touching first virtio buffer which carries header of >>packet, because someone could check that size of this buffer is equal >>to size of packet header. To send record, packet with start marker is >>sent first(it's header contains length of record and counter), then >>counter is incremented and all data is sent as usual 'RW' packets and >>finally SEQ_END is sent(it also carries counter of message, which is >>counter of SEQ_BEGIN + 1), also after sedning SEQ_END counter is >>incremented again. On receiver's side, length of record is known from >>packet with start record marker. To check that no packets were dropped >>by transport, counters of two sequential SEQ_BEGIN and SEQ_END are >>checked(counter of SEQ_END must be bigger that counter of SEQ_BEGIN by >>1) and length of data between two markers is compared to length in >>SEQ_BEGIN header. >> Now as packets of one socket are not reordered neither on >>vsock nor on vhost transport layers, such markers allows to restore >>original record on receiver's side. If user's buffer is smaller that >>record length, when all out of size data is dropped. >> Maximum length of datagram is not limited as in stream socket, >>because same credit logic is used. Difference with stream socket is >>that user is not woken up until whole record is received or error >>occurred. Implementation also supports 'MSG_EOR' and 'MSG_TRUNC' flags. >> Tests also implemented. > >I reviewed the first part (af_vsock.c changes), tomorrow I'll review >the rest. That part looks great to me, only found a few minor issues. I revieiwed the rest of it as well, left a few minor comments, but I think we're well on track. I'll take a better look at the specification patch tomorrow. Thanks, Stefano > >In the meantime, however, I'm getting a doubt, especially with regard >to other transports besides virtio. > >Should we hide the begin/end marker sending in the transport? > >I mean, should the transport just provide a seqpacket_enqueue() >callbacl? >Inside it then the transport will send the markers. This is because >some transports might not need to send markers. > >But thinking about it more, they could actually implement stubs for >that calls, if they don't need to send markers. > >So I think for now it's fine since it allows us to reuse a lot of >code, unless someone has some objection. > >Thanks, >Stefano >