Stefano Garzarella
2021-Feb-01 14:34 UTC
[RFC PATCH v3 00/13] virtio/vsock: introduce SOCK_SEQPACKET support
On Mon, Feb 01, 2021 at 05:32:00PM +0300, Arseny Krasnov wrote:> >On 01.02.2021 17:23, Stefano Garzarella wrote: >> On Mon, Feb 01, 2021 at 04:57:18PM +0300, Arseny Krasnov wrote: >>> On 01.02.2021 14:02, Stefano Garzarella wrote: >>>> On Fri, Jan 29, 2021 at 06:52:23PM +0300, Arseny Krasnov wrote: >>>>> On 29.01.2021 12:26, Stefano Garzarella wrote: >>>>>> On Fri, Jan 29, 2021 at 09:41:50AM +0300, Arseny Krasnov wrote: >>>>>>> On 28.01.2021 20:19, Stefano Garzarella wrote: >>>>>>>> Hi Arseny, >>>>>>>> I reviewed a part, tomorrow I hope to finish the other patches. >>>>>>>> >>>>>>>> Just a couple of comments in the TODOs below. >>>>>>>> >>>>>>>> On Mon, Jan 25, 2021 at 02:09:00PM +0300, Arseny Krasnov wrote: >>>>>>>>> This patchset impelements support of SOCK_SEQPACKET for virtio >>>>>>>>> transport. >>>>>>>>> As SOCK_SEQPACKET guarantees to save record boundaries, so to >>>>>>>>> do it, new packet operation was added: it marks start of record (with >>>>>>>>> record length in header), such packet doesn't carry any data. To send >>>>>>>>> record, packet with start marker is sent first, then all data is sent >>>>>>>>> as usual 'RW' packets. On receiver's side, length of record is known >>>>>>>> >from packet with start record marker. Now as packets of one socket >>>>>>>>> are not reordered neither on vsock nor on vhost transport layers, such >>>>>>>>> marker allows to restore original record on receiver's side. If user's >>>>>>>>> buffer is smaller that record length, when all out of size data is >>>>>>>>> dropped. >>>>>>>>> Maximum length of datagram is not limited as in stream socket, >>>>>>>>> because same credit logic is used. Difference with stream socket is >>>>>>>>> that user is not woken up until whole record is received or error >>>>>>>>> occurred. Implementation also supports 'MSG_EOR' and 'MSG_TRUNC' flags. >>>>>>>>> Tests also implemented. >>>>>>>>> >>>>>>>>> Arseny Krasnov (13): >>>>>>>>> af_vsock: prepare for SOCK_SEQPACKET support >>>>>>>>> af_vsock: prepare 'vsock_connectible_recvmsg()' >>>>>>>>> af_vsock: implement SEQPACKET rx loop >>>>>>>>> af_vsock: implement send logic for SOCK_SEQPACKET >>>>>>>>> af_vsock: rest of SEQPACKET support >>>>>>>>> af_vsock: update comments for stream sockets >>>>>>>>> virtio/vsock: dequeue callback for SOCK_SEQPACKET >>>>>>>>> virtio/vsock: fetch length for SEQPACKET record >>>>>>>>> virtio/vsock: add SEQPACKET receive logic >>>>>>>>> virtio/vsock: rest of SOCK_SEQPACKET support >>>>>>>>> virtio/vsock: setup SEQPACKET ops for transport >>>>>>>>> vhost/vsock: setup SEQPACKET ops for transport >>>>>>>>> vsock_test: add SOCK_SEQPACKET tests >>>>>>>>> >>>>>>>>> drivers/vhost/vsock.c | 7 +- >>>>>>>>> include/linux/virtio_vsock.h | 12 + >>>>>>>>> include/net/af_vsock.h | 6 + >>>>>>>>> include/uapi/linux/virtio_vsock.h | 9 + >>>>>>>>> net/vmw_vsock/af_vsock.c | 543 ++++++++++++++++------ >>>>>>>>> net/vmw_vsock/virtio_transport.c | 4 + >>>>>>>>> net/vmw_vsock/virtio_transport_common.c | 295 ++++++++++-- >>>>>>>>> tools/testing/vsock/util.c | 32 +- >>>>>>>>> tools/testing/vsock/util.h | 3 + >>>>>>>>> tools/testing/vsock/vsock_test.c | 126 +++++ >>>>>>>>> 10 files changed, 862 insertions(+), 175 deletions(-) >>>>>>>>> >>>>>>>>> TODO: >>>>>>>>> - Support for record integrity control. As transport could drop some >>>>>>>>> packets, something like "record-id" and record end marker need to >>>>>>>>> be implemented. Idea is that SEQ_BEGIN packet carries both record >>>>>>>>> length and record id, end marker(let it be SEQ_END) carries only >>>>>>>>> record id. To be sure that no one packet was lost, receiver checks >>>>>>>>> length of data between SEQ_BEGIN and SEQ_END(it must be same with >>>>>>>>> value in SEQ_BEGIN) and record ids of SEQ_BEGIN and SEQ_END(this >>>>>>>>> means that both markers were not dropped. I think that easiest way >>>>>>>>> to implement record id for SEQ_BEGIN is to reuse another field of >>>>>>>>> packet header(SEQ_BEGIN already uses 'flags' as record length).For >>>>>>>>> SEQ_END record id could be stored in 'flags'. >>>>>>>> I don't really like the idea of reusing the 'flags' field for this >>>>>>>> purpose. >>>>>>>> >>>>>>>>> Another way to implement it, is to move metadata of both SEQ_END >>>>>>>>> and SEQ_BEGIN to payload. But this approach has problem, because >>>>>>>>> if we move something to payload, such payload is accounted by >>>>>>>>> credit logic, which fragments payload, while payload with record >>>>>>>>> length and id couldn't be fragmented. One way to overcome it is to >>>>>>>>> ignore credit update for SEQ_BEGIN/SEQ_END packet.Another solution >>>>>>>>> is to update 'stream_has_space()' function: current implementation >>>>>>>>> return non-zero when at least 1 byte is allowed to use,but updated >>>>>>>>> version will have extra argument, which is needed length. For 'RW' >>>>>>>>> packet this argument is 1, for SEQ_BEGIN it is sizeof(record len + >>>>>>>>> record id) and for SEQ_END it is sizeof(record id). >>>>>>>> Is the payload accounted by credit logic also if hdr.op is not >>>>>>>> VIRTIO_VSOCK_OP_RW? >>>>>>> Yes, on send any packet with payload could be fragmented if >>>>>>> >>>>>>> there is not enough space at receiver. On receive 'fwd_cnt' and >>>>>>> >>>>>>> 'buf_alloc' are updated with header of every packet. Of course, >>>>>>> >>>>>>> to every such case i've described i can add check for 'RW' >>>>>>> >>>>>>> packet, to exclude payload from credit accounting, but this is >>>>>>> >>>>>>> bunch of dumb checks. >>>>>>> >>>>>>>> I think that we can define a specific header to put after the >>>>>>>> virtio_vsock_hdr when hdr.op is SEQ_BEGIN or SEQ_END, and in this header >>>>>>>> we can store the id and the length of the message. >>>>>>> I think it is better than use payload and touch credit logic >>>>>>> >>>>>> Cool, so let's try this option, hoping there aren't a lot of issues. >>>>> If i understand, current implementation has 'struct >>>>> virtio_vsock_hdr', >>>>> >>>>> then i'll add 'struct virtio_vsock_hdr_seq' with message length and id. >>>>> >>>>> After that, in 'struct virtio_vsock_pkt' which describes packet, field for >>>>> >>>>> header(which is 'struct virtio_vsock_hdr') must be replaced with new >>>>> >>>>> structure which? contains both 'struct virtio_vsock_hdr' and 'struct >>>>> >>>>> virtio_vsock_hdr_seq', because header field of 'struct virtio_vsock_pkt' >>>>> >>>>> is buffer for virtio layer. After it all accesses to header(for example to >>>>> >>>>> 'buf_alloc' field will go accross new? structure with both headers: >>>>> >>>>> pkt->hdr.buf_alloc?? ->?? pkt->extended_hdr.classic_hdr.buf_alloc >>>>> >>>>> May be to avoid this, packet's header could be allocated dynamically >>>>> >>>>> in the same manner as packet's buffer? Size of allocation is always >>>>> >>>>> sizeof(classic header) + sizeof(seq header). In 'struct virtio_vsock_pkt' >>>>> >>>>> such header will be implemented as union of two pointers: class header >>>>> >>>>> and extended header containing classic and seq header. Which pointer >>>>> >>>>> to use is depends on packet's op. >>>> I think that the 'classic header' can stay as is, and the extended >>>> header can be dynamically allocated, as we do for the payload. >>>> >>>> But we have to be careful what happens if the other peer doesn't support >>>> SEQPACKET and if it counts this extra header as a payload for the credit >>>> mechanism. >>> You mean put extra header to payload(buffer of second virtio desc), >>> >>> in this way on send/receive auxiliary 'if's are needed to avoid credit >>> >>> logic(or set length field in header of such packets to 0). But what >>> >>> about placing extra header after classic header in buffer of first virtio >>> >>> desc? In this case extra header is not payload and credit works as is. >>> >>> Or it is critical, that size of first buffer will be not same as size of >>> >>> classic header? >> We need to think about compatibility with old drivers. >Yes, compatibility seems to be a trouble. >> >> What would happen in this case? >> >> I think it's easier to use the second buffer, usually used for the >> payload, to carry the extra header. Also, we can leave hdr.len = 0, so >> we are sure that it is not counted in credit mechanism. > >Ok, that one of possible solutions. I just wanted to inform you, > >that way i'll use in v4 > >> If the driver supports SEQPACKET, it knows it must fetch extra header >> when it must handle SEQ_BEGIN/SEQ_END. >> >> If it is not clear, I'll try to provide a simple PoC of a patch. > >No, it is clear for me, i'll implement it in v4 also take care of > >review comments.Great! Let me know if any issues we haven't considered come up. Stefano