linux-kernel - Re: [RFC PATCH v7 12/22] virtio/vsock: fetch length for SEQPACKET record

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Date:   Thu, 25 Mar 2021 19:02:52 +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>,
        Alexander Popov <alex.popov@...ux.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 v7 12/22] virtio/vsock: fetch length for SEQPACKET
 record


On 25.03.2021 13:08, Stefano Garzarella wrote:
> On Tue, Mar 23, 2021 at 04:12:55PM +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>
>> ---
>> v6 -> v7:
>> 1) Now 'virtio_transport_seqpacket_seq_get_len()' returns 0, if rx
>>    queue of socket is empty. Else it returns length of current message
>>    to handle.
>> 2) If dequeue callback is called, but there is no detected length of
>>    message to dequeue, EAGAIN is returned, and outer loop restarts
>>    receiving.
>>
>> net/vmw_vsock/virtio_transport_common.c | 61 +++++++++++++++++++++++++
>> 1 file changed, 61 insertions(+)
>>
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index a8f4326e45e8..41f05034593e 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -399,6 +399,62 @@ 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;
>> +}
>> +
>> +static 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 = 0;
>> +
>> +	vvs = vsk->trans;
>> +
>> +	spin_lock_bh(&vvs->rx_lock);
>> +
>> +	/* Have some record to process, return it's length. */
>> +	if (vvs->seq_state.user_read_seq_len)
>> +		goto out;
>> +
>> +	/* 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;
>> +
>> +	pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
>> +
>> +	vvs->seq_state.user_read_copied = 0;
>> +
>> +	seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
>> +	vvs->seq_state.user_read_seq_len = le32_to_cpu(seq_hdr->msg_len);
>> +	vvs->seq_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->seq_state.user_read_seq_len;
>> +}
>> +
>> static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
>> 						 struct msghdr *msg,
>> 						 bool *msg_ready)
>> @@ -522,6 +578,11 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
>> 	if (flags & MSG_PEEK)
>> 		return -EOPNOTSUPP;
>>
>> +	*msg_len = virtio_transport_seqpacket_seq_get_len(vsk);
>> +
>> +	if (*msg_len == 0)
>> +		return -EAGAIN;
>> +
> Okay, I see now, I think you can move this patch before the previous one 
> or merge them in a single patch, it is better to review and to bisect.
>
> As mentioned, I think we can return msg_len if 
> virtio_transport_seqpacket_do_dequeue() does not fail, otherwise the 
> error.
>
> I mean something like this:
>
> static ssize_t virtio_transport_seqpacket_do_dequeue(...)
> {
> 	size_t msg_len;
> 	ssize_t ret;
>
> 	msg_len = virtio_transport_seqpacket_seq_get_len(vsk);
> 	if (msg_len == 0)
> 		return -EAGAIN;
>
> 	ret = virtio_transport_seqpacket_do_dequeue(vsk, msg, msg_ready);
> 	if (ret < 0)
> 		return ret;
>
> 	return msg_len;
> }
Ack
>
>> 	return virtio_transport_seqpacket_do_dequeue(vsk, msg, msg_ready);
>> }
>> EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
>> -- 2.25.1
>>
>