Stefano Garzarella
2021-Jan-29 09:26 UTC
[RFC PATCH v3 00/13] virtio/vsock: introduce SOCK_SEQPACKET support
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. Another item for TODO could be to add the SOCK_SEQPACKET support also for vsock_loopback. Should be simple since it also uses virtio_transport_common APIs and it can be useful for testing and debugging. Thanks, Stefano