linux-kernel - Re: [RFC PATCH v9 11/19] virtio/vsock: dequeue callback for SOCK

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Message-ID: <ff5e7e54-e56a-6574-2654-4afc3f10a28c@kaspersky.com>
Date:   Thu, 13 May 2021 17:42:47 +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>,
        Andra Paraschiv <andraprs@...zon.com>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        "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>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v9 11/19] virtio/vsock: dequeue callback for
 SOCK_SEQPACKET


On 13.05.2021 14:58, Stefano Garzarella wrote:
> On Sat, May 08, 2021 at 07:35:20PM +0300, Arseny Krasnov wrote:
>> This adds transport callback and it's logic for SEQPACKET dequeue.
>> 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>
>> ---
>> v8 -> v9:
>> 1) Check for RW packet type is removed from loop(all packet now
>>    considered RW).
>> 2) Locking in loop is fixed.
>> 3) cpu_to_le32()/le32_to_cpu() now used.
>> 4) MSG_TRUNC handling removed from transport.
>>
>> include/linux/virtio_vsock.h            |  5 ++
>> net/vmw_vsock/virtio_transport_common.c | 64 +++++++++++++++++++++++++
>> 2 files changed, 69 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..f649a21dd23b 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -393,6 +393,58 @@ 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 err = 0;
>> +	size_t user_buf_len = msg->msg_iter.count;
>> +
>> +	*msg_ready = false;
>> +	spin_lock_bh(&vvs->rx_lock);
>> +
>> +	while (!*msg_ready && !list_empty(&vvs->rx_queue) && err >= 0) {
>> +		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)) 
>> {
>> +				err = -EINVAL;
>> +			} else {
>> +				err += pkt_len;
> If `bytes_to_copy == 0` we are not increasing the real length.
>
> Anyway is a bit confusing increase a variable called `err`, I think is 
> better to have another variable to store this information that we return 
> if there aren't errors.
Ack
>
>