Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Arseny Krasnov <firstname.lastname@example.org>
To: Stefano Garzarella <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: Thu, 5 Aug 2021 12:21:57 +0300 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
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() 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 :
> Terminates a record (if supported by the protocol).
> From recvmsg() description :
> End-of-record was received (if supported by the protocol).
>  https://pubs.opengroup.org/onlinepubs/9699919799/functions/send.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
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.
next prev parent 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
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:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--subject='Re: ['\!''\!'Mass Mail KSE][MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET' \
* 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).