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[79.34.249.199]) by smtp.gmail.com with ESMTPSA id g18sm2173103wrw.40.2021.02.24.00.35.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Feb 2021 00:35:19 -0800 (PST) Date: Wed, 24 Feb 2021 09:35:16 +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: <20210224083516.kkxlkoin632iaqik@steredhat> References: <20210218053347.1066159-1-arseny.krasnov@kaspersky.com> <20210222142311.gekdd7gsm33wglos@steredhat> <20210223145016.ddavx6fihq4akdim@steredhat> <7a280168-cb54-ae26-4697-c797f6b04708@kaspersky.com> <20210224082319.yrmqr6zs7emvghw3@steredhat> <710d9dc2-3a0c-ea0b-fb02-68b460e6282e@kaspersky.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <710d9dc2-3a0c-ea0b-fb02-68b460e6282e@kaspersky.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Feb 24, 2021 at 11:28:50AM +0300, Arseny Krasnov wrote: > >On 24.02.2021 11:23, Stefano Garzarella wrote: >> On Wed, Feb 24, 2021 at 07:29:25AM +0300, Arseny Krasnov wrote: >>> On 23.02.2021 17:50, Stefano Garzarella wrote: >>>> 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. >>> Great, Thank You >>>> 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. >>> I thought about that, I'll try to implement it in next version. Let's see... >> If you want to discuss it first, write down the idea you want to >> implement, I wouldn't want to make you do unnecessary work. :-) > >Idea is simple, in iov iterator of 'struct msghdr' which is passed to > >enqueue callback we have two fields: 'iov_offset' which is byte > >offset inside io vector where next data must be picked and 'count' > >which is rest of unprocessed bytes in io vector. So in seqpacket > >enqueue callback if 'iov_offset' is 0 i'll send SEQBEGIN, and if > >'count' is 0 i'll send SEQEND. > Got it, make sense and it's defently more transparent for the vsock core! Go head, maybe adding a comment in the vsock core explaining this, so other developers can understand better if they want to support SEPACKET in other transports. Thanks, Stefano