Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Stefano Garzarella]

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.
>	Record has unlimited length, it consists of multiple message,
>and bounds of record are visible via MSG_EOR flag returned from
>'recvmsg()' call. Sender passes MSG_EOR to sending system call and
>receiver will see MSG_EOR when corresponding message will be processed.
>	To support MSG_EOR new bit was added along with existing
>'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
>works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
>is used to mark 'MSG_EOR' bit passed from userspace.

At this point it's probably better to rename the old flag, so we stay 
compatible.

What happens if one of the two peers does not support MSG_EOR handling, 
while the other does?

I'll do a closer review in the next few days.

Thanks,
Stefano

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Re: [MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Stefano Garzarella]

On Tue, Jul 27, 2021 at 12:34:36PM +0300, Arseny Krasnov wrote:
>
>On 27.07.2021 10:59, Stefano Garzarella wrote:
>> Caution: This is an external email. Be cautious while opening links or attachments.
>>
>>
>>
>> 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.
>>>       Record has unlimited length, it consists of multiple message,
>>> and bounds of record are visible via MSG_EOR flag returned from
>>> 'recvmsg()' call. Sender passes MSG_EOR to sending system call and
>>> receiver will see MSG_EOR when corresponding message will be processed.
>>>       To support MSG_EOR new bit was added along with existing
>>> 'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
>>> works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
>>> is used to mark 'MSG_EOR' bit passed from userspace.
>> At this point it's probably better to rename the old flag, so we stay
>> compatible.
>>
>> What happens if one of the two peers does not support MSG_EOR handling,
>> while the other does?
>>
>> I'll do a closer review in the next few days.
>Thank You, also i think MSG_EOR support must be described in spec

Yep, sure!

What do you think about the concerns above?

Stefano

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Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Stefano Garzarella]

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...

>	Record has unlimited length, it consists of multiple message,
>and bounds of record are visible via MSG_EOR flag returned from
>'recvmsg()' call. Sender passes MSG_EOR to sending system call and
>receiver will see MSG_EOR when corresponding message will be processed.
>	To support MSG_EOR new bit was added along with existing
>'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
>works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
>is used to mark 'MSG_EOR' bit passed from userspace.

I understand that it makes sense to remap VIRTIO_VSOCK_SEQ_EOR to 
MSG_EOR to make the user understand the boundaries, but why do we need 
EOM as well?

Why do we care about the boundaries of a message within a record?
I mean, if the sender makes 3 calls:
     send(A1,0)
     send(A2,0)
     send(A3, MSG_EOR);

IIUC it should be fine if the receiver for example receives all in one 
single recv() calll with MSG_EOR set, so why do we need EOM?

Thanks,
Stefano

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Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Stefano Garzarella]

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]:

   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.

 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

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Re: [!!Mass Mail KSE][MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

[Stefano Garzarella]

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...
>>> 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.
>

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 :-)

Stefano

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Re: [RFC PATCH v1 1/7] virtio/vsock: add 'VIRTIO_VSOCK_SEQ_EOM' bit

[Stefano Garzarella]

On Mon, Jul 26, 2021 at 07:33:04PM +0300, Arseny Krasnov wrote:
>This bit is used to mark end of messages('EOM' - end of message), while
>'VIRIO_VSOCK_SEQ_EOR' is used to pass MSG_EOR.
>
>Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>---
> include/uapi/linux/virtio_vsock.h | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>index 3dd3555b2740..1de3211a2988 100644
>--- a/include/uapi/linux/virtio_vsock.h
>+++ b/include/uapi/linux/virtio_vsock.h
>@@ -98,6 +98,7 @@ enum virtio_vsock_shutdown {
> /* VIRTIO_VSOCK_OP_RW flags values */
> enum virtio_vsock_rw {
> 	VIRTIO_VSOCK_SEQ_EOR = 1,
>+	VIRTIO_VSOCK_SEQ_EOM = 2,
> };

Already said, but I'll repeat it for completeness.

It's better to rename the flag 1 and use it in the same way we did 
before, so it's backward compatible.

Obviously we have to update the specifications too, explaining the 
difference between the two :-)

Thanks,
Stefano

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Re: [RFC PATCH v1 2/7] vsock: rename implementation from 'record' to 'message'

[Stefano Garzarella]

On Mon, Jul 26, 2021 at 07:33:25PM +0300, Arseny Krasnov wrote:
>As 'record' is not same as 'message', rename current variables,
>comments and defines from 'record' concept to 'message'.
>
>Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>---
> drivers/vhost/vsock.c                   | 18 +++++++++---------
> net/vmw_vsock/virtio_transport_common.c | 14 +++++++-------
> 2 files changed, 16 insertions(+), 16 deletions(-)


This patch is fine, I think you can move here the renaming of the flag 
too.

Stefano

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Re: [RFC PATCH v1 3/7] vhost/vsock: support MSG_EOR bit processing

[Stefano Garzarella]

On Mon, Jul 26, 2021 at 07:33:38PM +0300, Arseny Krasnov wrote:
>It works in the same way as 'end-of-message' bit: if packet has
>'EOM' bit, also check for 'EOR' bit.
>
>Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>---
> drivers/vhost/vsock.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 3b55de70ac77..3e2b150f9c6f 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -115,6 +115,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		size_t iov_len, payload_len;
> 		int head;
> 		bool restore_msg_eom_flag = false;
>+		bool restore_msg_eor_flag = false;

Since we now have 2 flags to potentially restore, we could use a single
variable (e.g. uint32_t flags_to_restore), initialized to 0.

We can set all the flags we need to restore and then simply put it
in or with the `pkt->hdr.flags` field.

> 		spin_lock_bh(&vsock->send_pkt_list_lock);
> 		if (list_empty(&vsock->send_pkt_list)) {
>@@ -188,6 +189,11 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 			if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM) {
> 				pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
> 				restore_msg_eom_flag = true;
>+
>+				if (le32_to_cpu(pkt->hdr.flags & VIRTIO_VSOCK_SEQ_EOR)) {
                                                                ^
Here it should be `le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR`

>+					pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>+					restore_msg_eor_flag = true;
>+				}
> 			}
> 		}
>
>@@ -224,9 +230,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		 * to send it with the next available buffer.
> 		 */
> 		if (pkt->off < pkt->len) {
>-			if (restore_msg_eom_flag)
>+			if (restore_msg_eom_flag) {
> 				pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>
>+				if (restore_msg_eor_flag)
>+					pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>+			}
>+

If we use a single variable, here we can simply do:

			pkt->hdr.flags |= cpu_to_le32(flags_to_restore);

Stefano

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Re: [RFC PATCH v1 3/7] vhost/vsock: support MSG_EOR bit processing

[Stefano Garzarella]

On Fri, Aug 06, 2021 at 11:40:38AM +0300, Arseny Krasnov wrote:
>
>On 06.08.2021 10:28, Stefano Garzarella wrote:
>> Caution: This is an external email. Be cautious while opening links or attachments.
>>
>>
>>
>> On Mon, Jul 26, 2021 at 07:33:38PM +0300, Arseny Krasnov wrote:
>>> It works in the same way as 'end-of-message' bit: if packet has
>>> 'EOM' bit, also check for 'EOR' bit.
>>>
>>> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>>> ---
>>> drivers/vhost/vsock.c | 12 +++++++++++-
>>> 1 file changed, 11 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>>> index 3b55de70ac77..3e2b150f9c6f 100644
>>> --- a/drivers/vhost/vsock.c
>>> +++ b/drivers/vhost/vsock.c
>>> @@ -115,6 +115,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>>>               size_t iov_len, payload_len;
>>>               int head;
>>>               bool restore_msg_eom_flag = false;
>>> +              bool restore_msg_eor_flag = false;
>> Since we now have 2 flags to potentially restore, we could use a single
>> variable (e.g. uint32_t flags_to_restore), initialized to 0.
>>
>> We can set all the flags we need to restore and then simply put it
>> in or with the `pkt->hdr.flags` field.
>>
>>>               spin_lock_bh(&vsock->send_pkt_list_lock);
>>>               if (list_empty(&vsock->send_pkt_list)) {
>>> @@ -188,6 +189,11 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>>>                       if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM) {
>>>                               pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>>>                               restore_msg_eom_flag = true;
>>> +
>>> +                              if (le32_to_cpu(pkt->hdr.flags & VIRTIO_VSOCK_SEQ_EOR)) {
>>                                                                 ^
>> Here it should be `le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR`
>>
>>> +                                      pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>>> +                                      restore_msg_eor_flag = true;
>>> +                              }
>>>                       }
>>>               }
>>>
>>> @@ -224,9 +230,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>>>                * to send it with the next available buffer.
>>>                */
>>>               if (pkt->off < pkt->len) {
>>> -                      if (restore_msg_eom_flag)
>>> +                      if (restore_msg_eom_flag) {
>>>                               pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>>>
>>> +                              if (restore_msg_eor_flag)
>>> +                                      pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>>> +                      }
>>> +
>> If we use a single variable, here we can simply do:
>>
>>                         pkt->hdr.flags |= cpu_to_le32(flags_to_restore);
>>
>> Stefano
>
>Thanks, i'll prepare v2 both with spec patch. About spec: i've already sent
>
>patch for SEQPACKET, can i prepare spec patch updating current reviewed
>
>SEQPACKET? E.g. i'll include both EOM and EOR in one patch.

Yep, since spec is not yet merged, I think make sense to have all 
seqpacket stuff in a single patch.

Thanks,
Stefano

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