netdev - Re: [RFC PATCH v6 04/22] af_vsock: implement SEQPACKET receive loop

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Date:   Mon, 15 Mar 2021 10:49:32 +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>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        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>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v6 04/22] af_vsock: implement SEQPACKET receive loop


On 12.03.2021 18:17, Stefano Garzarella wrote:
> On Sun, Mar 07, 2021 at 08:59:45PM +0300, Arseny Krasnov wrote:
>> This adds receive loop for SEQPACKET. It looks like receive loop for
>> STREAM, but there is a little bit difference:
>> 1) It doesn't call notify callbacks.
>> 2) It doesn't care about 'SO_SNDLOWAT' and 'SO_RCVLOWAT' values, because
>>   there is no sense for these values in SEQPACKET case.
>> 3) It waits until whole record is received or error is found during
>>   receiving.
>> 4) It processes and sets 'MSG_TRUNC' flag.
>>
>> So to avoid extra conditions for two types of socket inside one loop, two
>> independent functions were created.
>>
>> Signed-off-by: Arseny Krasnov <arseny.krasnov@...persky.com>
>> ---
>> include/net/af_vsock.h   |  5 +++
>> net/vmw_vsock/af_vsock.c | 95 +++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 99 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> index b1c717286993..5ad7ee7f78fd 100644
>> --- a/include/net/af_vsock.h
>> +++ b/include/net/af_vsock.h
>> @@ -135,6 +135,11 @@ struct vsock_transport {
>> 	bool (*stream_is_active)(struct vsock_sock *);
>> 	bool (*stream_allow)(u32 cid, u32 port);
>>
>> +	/* SEQ_PACKET. */
>> +	size_t (*seqpacket_seq_get_len)(struct vsock_sock *vsk);
>> +	int (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
>> +				 int flags, bool *msg_ready);
>> +
>> 	/* Notification. */
>> 	int (*notify_poll_in)(struct vsock_sock *, size_t, bool *);
>> 	int (*notify_poll_out)(struct vsock_sock *, size_t, bool *);
>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>> index 0bc661e54262..ac2f69362f2e 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -1973,6 +1973,96 @@ static int __vsock_stream_recvmsg(struct sock *sk, struct msghdr *msg,
>> 	return err;
>> }
>>
>> +static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr *msg,
>> +				     size_t len, int flags)
>> +{
>> +	const struct vsock_transport *transport;
>> +	const struct iovec *orig_iov;
>> +	unsigned long orig_nr_segs;
>> +	bool msg_ready;
>> +	struct vsock_sock *vsk;
>> +	size_t record_len;
>> +	long timeout;
>> +	int err = 0;
>> +	DEFINE_WAIT(wait);
>> +
>> +	vsk = vsock_sk(sk);
>> +	transport = vsk->transport;
>> +
>> +	timeout = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
>> +	orig_nr_segs = msg->msg_iter.nr_segs;
>> +	orig_iov = msg->msg_iter.iov;
>> +	msg_ready = false;
>> +	record_len = 0;
>> +
>> +	while (1) {
>> +		err = vsock_wait_data(sk, &wait, timeout, NULL, 0);
>> +
>> +		if (err <= 0) {
>> +			/* In case of any loop break(timeout, signal
>> +			 * interrupt or shutdown), we report user that
>> +			 * nothing was copied.
>> +			 */
>> +			err = 0;
>> +			break;
>> +		}
>> +
>> +		if (record_len == 0) {
>> +			record_len =
>> +				transport->seqpacket_seq_get_len(vsk);
>> +
>> +			if (record_len == 0)
>> +				continue;
>> +		}
>> +
>> +		err = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready);
> In order to simplify the transport interface, can we do the work of 
> seqpacket_seq_get_len() at the beginning of seqpacket_dequeue()?
>
> So in this way seqpacket_dequeue() can return the 'record_len' or an 
> error.
Ack
>
>