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

From: Arseny Krasnov
Date: Tue Jul 27 2021 - 05:36:07 EST



On 27.07.2021 10:59, Stefano Garzarella wrote:
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> 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?
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> I'll do a closer review in the next few days.
Thank You, also i think MSG_EOR support must be described in spec
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> Thanks,
> Stefano
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