linux-kernel - Re: [RFC PATCH v6 12/22] virtio/vsock: fetch length for SEQPACKET record

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Date:   Mon, 15 Mar 2021 10:49:05 +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>,
        Norbert Slusarek <nslusarek@....net>,
        Colin Ian King <colin.king@...onical.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>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v6 12/22] virtio/vsock: fetch length for SEQPACKET
 record


On 12.03.2021 18:20, Stefano Garzarella wrote:
> On Sun, Mar 07, 2021 at 09:02:31PM +0300, Arseny Krasnov wrote:
>> This adds transport callback which tries to fetch record begin marker
> >from socket's rx queue. It is called from af_vsock.c before reading data
>> packets of record.
>>
>> Signed-off-by: Arseny Krasnov <arseny.krasnov@...persky.com>
>> ---
>> include/linux/virtio_vsock.h            |  1 +
>> net/vmw_vsock/virtio_transport_common.c | 53 +++++++++++++++++++++++++
>> 2 files changed, 54 insertions(+)
>>
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index 466a5832d2f5..d7edcfeb4cd2 100644
>> --- a/include/linux/virtio_vsock.h
>> +++ b/include/linux/virtio_vsock.h
>> @@ -88,6 +88,7 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>> 			       struct msghdr *msg,
>> 			       size_t len, int flags);
>>
>> +size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk);
>> int
>> virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
>> 				   struct msghdr *msg,
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 5f1e283e43f3..6fc78fec41c0 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -399,6 +399,59 @@ static inline void virtio_transport_remove_pkt(struct virtio_vsock_pkt *pkt)
>> 	virtio_transport_free_pkt(pkt);
>> }
>>
>> +static size_t virtio_transport_drop_until_seq_begin(struct virtio_vsock_sock *vvs)
>> +{
>> +	struct virtio_vsock_pkt *pkt, *n;
>> +	size_t bytes_dropped = 0;
>> +
>> +	list_for_each_entry_safe(pkt, n, &vvs->rx_queue, list) {
>> +		if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_SEQ_BEGIN)
>> +			break;
>> +
>> +		bytes_dropped += le32_to_cpu(pkt->hdr.len);
>> +		virtio_transport_dec_rx_pkt(vvs, pkt);
>> +		virtio_transport_remove_pkt(pkt);
>> +	}
>> +
>> +	return bytes_dropped;
>> +}
>> +
>> +size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk)
>> +{
>> +	struct virtio_vsock_seq_hdr *seq_hdr;
>> +	struct virtio_vsock_sock *vvs;
>> +	struct virtio_vsock_pkt *pkt;
>> +	size_t bytes_dropped;
>> +
>> +	vvs = vsk->trans;
>> +
>> +	spin_lock_bh(&vvs->rx_lock);
>> +
>> +	/* Fetch all orphaned 'RW' packets and send credit update. */
>> +	bytes_dropped = virtio_transport_drop_until_seq_begin(vvs);
>> +
>> +	if (list_empty(&vvs->rx_queue))
>> +		goto out;
> What do we return to in this case?
>
> IIUC we return the len of the previous packet, should we set 
> vvs->seqpacket_state.user_read_seq_len to 0?
Yes, i think that's true
>
>> +
>> +	pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
>> +
>> +	vvs->seqpacket_state.user_read_copied = 0;
>> +
>> +	seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
>> +	vvs->seqpacket_state.user_read_seq_len = 
>> le32_to_cpu(seq_hdr->msg_len);
>> +	vvs->seqpacket_state.curr_rx_msg_id = le32_to_cpu(seq_hdr->msg_id);
>> +	virtio_transport_dec_rx_pkt(vvs, pkt);
>> +	virtio_transport_remove_pkt(pkt);
>> +out:
>> +	spin_unlock_bh(&vvs->rx_lock);
>> +
>> +	if (bytes_dropped)
>> +		virtio_transport_send_credit_update(vsk);
>> +
>> +	return vvs->seqpacket_state.user_read_seq_len;
>> +}
>> +EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_seq_get_len);
>> +
>> static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
>> 						 struct msghdr *msg,
>> 						 bool *msg_ready)
>> -- 
>> 2.25.1
>>
>