Messages in this thread | | | Date | Tue, 8 Jun 2021 10:23:20 +0200 | From | Stefano Garzarella <> | Subject | Re: [PATCH v10 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET |
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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.
Stefano
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