Messages in this thread | | | Date | Tue, 8 Jun 2021 12:19:52 +0200 | From | Stefano Garzarella <> | Subject | Re: [PATCH v10 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET |
| |
On Tue, Jun 08, 2021 at 12:40:39PM +0300, Arseny Krasnov wrote: > >On 08.06.2021 11:23, Stefano Garzarella wrote: >> On Mon, Jun 07, 2021 at 04:18:38PM +0300, Arseny Krasnov wrote: >>> On 07.06.2021 14:04, Stefano Garzarella wrote: >>>> On Fri, Jun 04, 2021 at 09:03:26PM +0300, Arseny Krasnov wrote: >>>>> On 04.06.2021 18:03, Stefano Garzarella wrote: >>>>>> 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@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. >>>>> Hm, yes, this is problem. To solve it i can restore previous approach >>>>> with seqbegin/seqend. In that case i can detect unfinished record and >>>>> drop it's packets. Seems seqbegin will be a bit like >>>>> VIRTIO_VSOCK_SEQ_EOR in flags >>>>> field of header(e.g. VIRTIO_VSOCK_SEQ_BEGIN). Message id and length are >>>>> unneeded, >>>>> as channel considedered lossless. What do You think? >>>>> >>>> I think VIRTIO_VSOCK_SEQ_BEGIN is redundant, using only EOR should be >>>> fine. >>>> >>>> When we receive EOR we know that this is the last packet on this message >>>> and the next packet will be the first of a new message. >>>> >>>> What we should do is check that we have all the fragments of a packet >>>> and return them all together, otherwise we have to say we have nothing. >>>> >>>> For example as we process packets from the vitqueue and queue them in >>>> the rx_queue we could use a counter of how many EORs are in the >>>> rx_queue, which we decrease in virtio_transport_seqpacket_do_dequeue() >>>> when we copied all the fragments. >>>> >>>> If the counter is 0, we don't remove anything from the queue and >>>> virtio_transport_seqpacket_do_dequeue() returns 0. >>>> >>>> So .seqpacket_dequeue should return 0 if there is not at least one >>>> complete message, or return the entire message. A partial message should >>>> never return. >>>> >>>> What do you think? >>> I like it, i've implemented this approach in some early pre v1 versions. >>> >>> But in this case, credit update logic will be changed - in current implementation >>> >>> (both seqpacket and stream) credit update reply is sent when data is copied >>> >>> to user's buffer(e.g. we copy data somewhere, free packet and ready to process >>> >>> new packet). But if we don't touch user's buffer and keeping incoming packet in rx queue >>> >>> until whole record is ready, when to send credit update? >> I think the best approach could be to send credit updates when we remove >> them from the rx_queue. > >In that case, it will be impossible to send message bigger than size of rx buffer > >(e.g. credit allowed size), because packet will be queued without credit update > >reply until credit allowed reach 0. >
Yep, but I think it is a reasonable limit for a datagram socket.
Maybe we can add a check on the TX side, since we know this value and return an error to the user.
Thanks, Stefano
| |