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From: Stefano Garzarella <>
To: Arseny Krasnov <>
Cc: Stefan Hajnoczi <>,
	"Michael S. Tsirkin" <>,
	Jason Wang <>,
	"David S. Miller" <>,
	Jakub Kicinski <>,
	Colin Ian King <>,
	Andra Paraschiv <>,
	Norbert Slusarek <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET
Date: Thu, 5 Aug 2021 11:06:57 +0200	[thread overview]
Message-ID: <20210805090657.y2sz3pzhruuolncq@steredhat> (raw)
In-Reply-To: <>

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 [1]:

     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() and 
received, for example, with a single recvmsg().
The only boundary should be the MSG_EOR flag set by the user on the last 
send() of a record.

 From send() description [2]:

     Terminates a record (if supported by the protocol).

 From recvmsg() description [3]:

     End-of-record was received (if supported by the protocol).



  reply	other threads:[~2021-08-05  9:07 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 16:31 [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET 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 [this message]
2021-08-05  9:21       ` [!!Mass Mail KSE][MASSMAIL KLMS] " Arseny Krasnov
2021-08-06  7:16         ` Stefano Garzarella

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