Stefano Garzarella
2021-Jun-08 10:39 UTC
[PATCH v10 11/18] virtio/vsock: dequeue callback for SOCK_SEQPACKET
On Tue, Jun 08, 2021 at 01:24:58PM +0300, Arseny Krasnov wrote:> >On 08.06.2021 13:19, Stefano Garzarella wrote: >> 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 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. >>>>>>> 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. > >E.g., to before sending message? using SEQPACKET socket, > >i need to call setsockopt with SO_VM_SOCKETS_BUFFER_MAX_SIZE/ > >SO_VM_SOCKETS_BUFFER_SIZE params to setup maximum message size, > >if user tries to send message bigger than it, return -EMSGSIZE ? >Yep, I mean the receiver side must set it (IIRC default is 256K). In the transmitter side we can check it using `vvs->peer_buf_alloc` and return the error. Stefano