Stefano Garzarella
2021-Jun-04 15:03 UTC
[PATCH v10 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET
On Fri, Jun 04, 2021 at 04:12:23PM +0300, Arseny Krasnov wrote:> >On 03.06.2021 17:45, Stefano Garzarella wrote: >> On Thu, May 20, 2021 at 10:17:58PM +0300, Arseny Krasnov wrote: >>> Callback fetches RW packets from rx queue of socket until whole record >>> is copied(if user's buffer is full, user is not woken up). This is done >>> to not stall sender, because if we wake up user and it leaves syscall, >>> nobody will send credit update for rest of record, and sender will wait >>> for next enter of read syscall at receiver's side. So if user buffer is >>> full, we just send credit update and drop data. >>> >>> Signed-off-by: Arseny Krasnov <arseny.krasnov at kaspersky.com> >>> --- >>> v9 -> v10: >>> 1) Number of dequeued bytes incremented even in case when >>> user's buffer is full. >>> 2) Use 'msg_data_left()' instead of direct access to 'msg_hdr'. >>> 3) Rename variable 'err' to 'dequeued_len', in case of error >>> it has negative value. >>> >>> include/linux/virtio_vsock.h | 5 ++ >>> net/vmw_vsock/virtio_transport_common.c | 65 +++++++++++++++++++++++++ >>> 2 files changed, 70 insertions(+) >>> >>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h >>> index dc636b727179..02acf6e9ae04 100644 >>> --- a/include/linux/virtio_vsock.h >>> +++ b/include/linux/virtio_vsock.h >>> @@ -80,6 +80,11 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk, >>> struct msghdr *msg, >>> size_t len, int flags); >>> >>> +ssize_t >>> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk, >>> + struct msghdr *msg, >>> + int flags, >>> + bool *msg_ready); >>> s64 virtio_transport_stream_has_data(struct vsock_sock *vsk); >>> s64 virtio_transport_stream_has_space(struct vsock_sock *vsk); >>> >>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >>> index ad0d34d41444..61349b2ea7fe 100644 >>> --- a/net/vmw_vsock/virtio_transport_common.c >>> +++ b/net/vmw_vsock/virtio_transport_common.c >>> @@ -393,6 +393,59 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, >>> return err; >>> } >>> >>> +static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk, >>> + struct msghdr *msg, >>> + int flags, >>> + bool *msg_ready) >>> +{ >>> + struct virtio_vsock_sock *vvs = vsk->trans; >>> + struct virtio_vsock_pkt *pkt; >>> + int dequeued_len = 0; >>> + size_t user_buf_len = msg_data_left(msg); >>> + >>> + *msg_ready = false; >>> + spin_lock_bh(&vvs->rx_lock); >>> + >>> + while (!*msg_ready && !list_empty(&vvs->rx_queue) && dequeued_len >= 0) { >> I' >> >>> + size_t bytes_to_copy; >>> + size_t pkt_len; >>> + >>> + pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list); >>> + pkt_len = (size_t)le32_to_cpu(pkt->hdr.len); >>> + bytes_to_copy = min(user_buf_len, pkt_len); >>> + >>> + if (bytes_to_copy) { >>> + /* sk_lock is held by caller so no one else can dequeue. >>> + * Unlock rx_lock since memcpy_to_msg() may sleep. >>> + */ >>> + spin_unlock_bh(&vvs->rx_lock); >>> + >>> + if (memcpy_to_msg(msg, pkt->buf, bytes_to_copy)) >>> + dequeued_len = -EINVAL; >> I think here is better to return the error returned by memcpy_to_msg(), >> as we do in the other place where we use memcpy_to_msg(). >> >> I mean something like this: >> err = memcpy_to_msgmsg, pkt->buf, bytes_to_copy); >> if (err) >> dequeued_len = err; >Ack >>> + else >>> + user_buf_len -= bytes_to_copy; >>> + >>> + spin_lock_bh(&vvs->rx_lock); >>> + } >>> + >> Maybe here we can simply break the cycle if we have an error: >> if (dequeued_len < 0) >> break; >> >> Or we can refactor a bit, simplifying the while() condition and also the >> code in this way (not tested): >> >> while (!*msg_ready && !list_empty(&vvs->rx_queue)) { >> ... >> >> if (bytes_to_copy) { >> int err; >> >> /* ... >> */ >> spin_unlock_bh(&vvs->rx_lock); >> err = memcpy_to_msgmsg, pkt->buf, bytes_to_copy); >> if (err) { >> dequeued_len = err; >> goto out; >> } >> spin_lock_bh(&vvs->rx_lock); >> >> user_buf_len -= bytes_to_copy; >> } >> >> dequeued_len += pkt_len; >> >> if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR) >> *msg_ready = true; >> >> virtio_transport_dec_rx_pkt(vvs, pkt); >> list_del(&pkt->list); >> virtio_transport_free_pkt(pkt); >> } >> >> out: >> spin_unlock_bh(&vvs->rx_lock); >> >> virtio_transport_send_credit_update(vsk); >> >> return dequeued_len; >> } > >I think we can't do 'goto out' or break, because in case of error, we still need >to free packet.Didn't we have code that remove packets from a previous message? I don't see it anymore. For example if we have 10 packets queued for a message (the 10th packet has the EOR flag) and the memcpy_to_msg() fails on the 2nd packet, with you proposal we are freeing only the first 2 packets, the rest is there and should be freed when reading the next message, but I don't see that code. The same can happen if the recvmsg syscall is interrupted. In that case we report that nothing was copied, but we freed the first N packets, so they are lost but the other packets are still in the queue. Please check also the patch where we implemented __vsock_seqpacket_recvmsg(). I thinks we should free packets only when we are sure we copied them to the user space.> It is possible to do something like this: > > virtio_transport_dec_rx_pkt(vvs, pkt); > list_del(&pkt->list); > virtio_transport_free_pkt(pkt); > > if (dequeued_len < 0) > break; > >> >> >