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From: Stefano Garzarella <firstname.lastname@example.org>
To: Arseny Krasnov <email@example.com>
Cc: Stefan Hajnoczi <firstname.lastname@example.org>,
"Michael S. Tsirkin" <email@example.com>,
Jason Wang <firstname.lastname@example.org>,
"David S. Miller" <email@example.com>,
Jakub Kicinski <firstname.lastname@example.org>,
Colin Ian King <email@example.com>,
Andra Paraschiv <firstname.lastname@example.org>,
Norbert Slusarek <email@example.com>,
Subject: Re: [!!Mass Mail KSE][MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET
Date: Fri, 6 Aug 2021 09:16:43 +0200 [thread overview]
Message-ID: <20210806071643.byebg4hmm3dtnb2x@steredhat> (raw)
On Thu, Aug 05, 2021 at 12:21:57PM +0300, Arseny Krasnov wrote:
>On 05.08.2021 12:06, Stefano Garzarella wrote:
>> Caution: This is an external email. Be cautious while opening links or attachments.
>> On Thu, Aug 05, 2021 at 11:33:12AM +0300, Arseny Krasnov wrote:
>>> On 04.08.2021 15:57, Stefano Garzarella wrote:
>>>> Caution: This is an external email. Be cautious while opening links or attachments.
>>>> Hi Arseny,
>>>> On Mon, Jul 26, 2021 at 07:31:33PM +0300, Arseny Krasnov wrote:
>>>>> This patchset implements support of MSG_EOR bit for SEQPACKET
>>>>> AF_VSOCK sockets over virtio transport.
>>>>> Idea is to distinguish concepts of 'messages' and 'records'.
>>>>> Message is result of sending calls: 'write()', 'send()', 'sendmsg()'
>>>>> etc. It has fixed maximum length, and it bounds are visible using
>>>>> return from receive calls: 'read()', 'recv()', 'recvmsg()' etc.
>>>>> Current implementation based on message definition above.
>>>> Okay, so the implementation we merged is wrong right?
>>>> Should we disable the feature bit in stable kernels that contain it? Or
>>>> maybe we can backport the fixes...
>>> No, this is correct and it is message boundary based. Idea of this
>>> patchset is to add extra boundaries marker which i think could be
>>> useful when we want to send data in seqpacket mode which length
>>> is bigger than maximum message length(this is limited by transport).
>>> Of course we can fragment big piece of data too small messages, but
>>> requires to carry fragmentation info in data protocol. So In this case
>>> when we want to maintain boundaries receiver calls recvmsg() until
>>> MSG_EOR found.
>>> But when receiver knows, that data is fit in maximum datagram length,
>>> it doesn't care about checking MSG_EOR just calling recv() or
>>> message based mode).
>> I'm not sure we should maintain boundaries of multiple send(), from
>> POSIX standard :
>Yes, but also from POSIX: such calls like send() and sendmsg()
>operates with "message" and if we check recvmsg() we will
>find the following thing:
>For message-based sockets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire
>message shall be read in a single operation. If a message is too long to fit in the supplied
>buffers, and MSG_PEEK is not set in the flags argument, the excess bytes shall be discarded.
>I understand this, that send() boundaries also must be maintained.
>I've checked SEQPACKET in AF_UNIX and AX_25 - both doesn't support
>MSG_EOR, so send() boundaries must be supported.
>> Provides sequenced, reliable, bidirectional, connection-mode
>> transmission paths for records. A record can be sent using one or
>> more output operations and received using one or more input
>> operations, but a single operation never transfers part of more than
>> one record. Record boundaries are visible to the receiver via the
>> MSG_EOR flag.
>> From my understanding a record could be sent with multiple send()
>> received, for example, with a single recvmsg().
>> The only boundary should be the MSG_EOR flag set by the user on the
>> send() of a record.
>You are right, if we talking about "record".
>> From send() description :
>> Terminates a record (if supported by the protocol).
>> From recvmsg() description :
>> End-of-record was received (if supported by the protocol).
>P.S.: seems SEQPACKET is too exotic thing that everyone implements it
>own manner, because i've tested SCTP seqpacket implementation, and
>1) It doesn't support MSG_EOR bit at send side, but uses MSG_EOR at
>side to mark MESSAGE boundary.
>2) According POSIX any extra bytes that didn't fit in user's buffer
>must be dropped,
>but SCTP doesn't drop it - you can read rest of datagram in next calls.
Thanks for this useful information, now I see the differences and why we
should support both.
I think is better to include them in the cover letter.
I'm going to review the paches right now :-)
prev parent reply other threads:[~2021-08-06 7:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 16:31 Arseny Krasnov
2021-07-26 16:33 ` [RFC PATCH v1 1/7] virtio/vsock: add 'VIRTIO_VSOCK_SEQ_EOM' bit Arseny Krasnov
2021-08-06 7:18 ` Stefano Garzarella
2021-07-26 16:33 ` [RFC PATCH v1 2/7] vsock: rename implementation from 'record' to 'message' Arseny Krasnov
2021-08-06 7:20 ` Stefano Garzarella
2021-07-26 16:33 ` [RFC PATCH v1 3/7] vhost/vsock: support MSG_EOR bit processing Arseny Krasnov
2021-08-06 7:28 ` Stefano Garzarella
2021-08-06 8:40 ` Arseny Krasnov
2021-08-06 8:47 ` Stefano Garzarella
2021-07-26 16:33 ` [RFC PATCH v1 4/7] virito/vsock: " Arseny Krasnov
2021-07-26 16:34 ` [RFC PATCH v1 5/7] af_vsock: rename variables in receive loop Arseny Krasnov
2021-07-26 16:34 ` [RFC PATCH v1 6/7] vsock_test: update message bounds test for MSG_EOR Arseny Krasnov
2021-07-26 16:34 ` [RFC PATCH v1 7/7] vsock_test: 'SO_RCVTIMEO' test for SEQPACKET Arseny Krasnov
2021-07-27 7:59 ` [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag " Stefano Garzarella
2021-07-27 9:34 ` [MASSMAIL KLMS] " Arseny Krasnov
2021-07-27 9:58 ` Stefano Garzarella
2021-07-27 12:35 ` [MASSMAIL KLMS] " Arseny Krasnov
2021-08-04 12:57 ` Stefano Garzarella
2021-08-05 8:33 ` Arseny Krasnov
2021-08-05 9:06 ` Stefano Garzarella
2021-08-05 9:21 ` [!!Mass Mail KSE][MASSMAIL KLMS] " Arseny Krasnov
2021-08-06 7:16 ` Stefano Garzarella [this message]
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