LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Arseny Krasnov <arseny.krasnov@kaspersky.com>
To: Stefano Garzarella <sgarzare@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Colin Ian King <colin.king@canonical.com>,
	Andra Paraschiv <andraprs@amazon.com>,
	Norbert Slusarek <nslusarek@gmx.net>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"oxffffaa@gmail.com" <oxffffaa@gmail.com>
Subject: Re: [!!Mass Mail KSE][MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET
Date: Thu, 5 Aug 2021 12:21:57 +0300	[thread overview]
Message-ID: <8bd80d3f-3e00-5e31-42a1-300ff29100ae@kaspersky.com> (raw)
In-Reply-To: <20210805090657.y2sz3pzhruuolncq@steredhat>


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...
>> Hi,
>>
>> 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
>> this
>> 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
>> read()(e.g.
>> message based mode).
> I'm not sure we should maintain boundaries of multiple send(), from
> POSIX standard [1]:

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.

>
>    SOCK_SEQPACKET
>      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.
You are right, if we talking about "record".
>
>  From send() description [2]:
>
>    MSG_EOR
>      Terminates a record (if supported by the protocol).
>
>  From recvmsg() description [3]:
>
>    MSG_EOR
>      End-of-record was received (if supported by the protocol).
>
> Thanks,
> Stefano
>
> [1]
> https://pubs.opengroup.org/onlinepubs/9699919799/functions/socket.html
> [2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html
> [3]
> https://pubs.opengroup.org/onlinepubs/9699919799/functions/recvmsg.html

P.S.: seems SEQPACKET is too exotic thing that everyone implements it in

own manner, because i've tested SCTP seqpacket implementation, and found

that:

1) It doesn't support MSG_EOR bit at send side, but uses MSG_EOR at receiver

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.

>
>

  reply	other threads:[~2021-08-05  9:22 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       ` Arseny Krasnov [this message]
2021-08-06  7:16         ` [!!Mass Mail KSE][MASSMAIL KLMS] " Stefano Garzarella

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8bd80d3f-3e00-5e31-42a1-300ff29100ae@kaspersky.com \
    --to=arseny.krasnov@kaspersky.com \
    --cc=andraprs@amazon.com \
    --cc=colin.king@canonical.com \
    --cc=davem@davemloft.net \
    --cc=jasowang@redhat.com \
    --cc=kuba@kernel.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=nslusarek@gmx.net \
    --cc=oxffffaa@gmail.com \
    --cc=sgarzare@redhat.com \
    --cc=stefanha@redhat.com \
    --cc=virtualization@lists.linux-foundation.org \
    --subject='Re: ['\!''\!'Mass Mail KSE][MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).