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Message-ID: <6b833ccf-ea93-db6a-4743-463ac1cfe817@kaspersky.com>
Date: Fri, 4 Jun 2021 16:12:23 +0300
From: Arseny Krasnov <arseny.krasnov@...persky.com>
To: Stefano Garzarella <sgarzare@...hat.com>
CC: Stefan Hajnoczi <stefanha@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Jorgen Hansen <jhansen@...are.com>,
Norbert Slusarek <nslusarek@....net>,
Colin Ian King <colin.king@...onical.com>,
Andra Paraschiv <andraprs@...zon.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [PATCH v10 11/18] virtio/vsock: dequeue callback for
SOCK_SEQPACKET
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@...persky.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. 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;
>
>
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