Re: [RFC PATCH v3 03/13] af_vsock: implement SEQPACKET rx loop

[Arseny Krasnov]

On 28.01.2021 19:55, Stefano Garzarella wrote:
> On Mon, Jan 25, 2021 at 02:12:36PM +0300, Arseny Krasnov wrote:
>> This adds receive loop for SEQPACKET. It looks like receive loop for
>> SEQPACKET, 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@xxxxxxxxxxxxx>
>> ---
>> include/net/af_vsock.h   |   5 ++
>> net/vmw_vsock/af_vsock.c | 102 ++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 106 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> index b1c717286993..46073842d489 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 *);
>> +	ssize_t (*seqpacket_dequeue)(struct vsock_sock *, struct msghdr *,
>> +				     size_t len, int flags);
>> +
>> 	/* 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 524df8fc84cd..3b266880b7c8 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -2006,7 +2006,107 @@ static int __vsock_stream_recvmsg(struct sock *sk, struct msghdr *msg,
>> static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr *msg,
>> 				     size_t len, int flags)
>> {
>> -	return -1;
>> +	const struct vsock_transport *transport;
>> +	const struct iovec *orig_iov;
>> +	unsigned long orig_nr_segs;
>> +	ssize_t dequeued_total = 0;
>> +	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);
>> +	msg->msg_flags &= ~MSG_EOR;
> Maybe add a comment about why we need to clear MSG_EOR.
>
>> +	orig_nr_segs = msg->msg_iter.nr_segs;
>> +	orig_iov = msg->msg_iter.iov;
>> +
>> +	while (1) {
>> +		ssize_t dequeued;
>> +		s64 ready;
>> +
>> +		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
>> +		ready = vsock_stream_has_data(vsk);
>> +
>> +		if (ready == 0) {
>> +			if (vsock_wait_data(sk, &wait, timeout, NULL, 0)) {
>> +				/* In case of any loop break(timeout, signal
>> +				 * interrupt or shutdown), we report user that
>> +				 * nothing was copied.
>> +				 */
>> +				dequeued_total = 0;
>> +				break;
>> +			}
>> +			continue;
>> +		}
>> +
>> +		finish_wait(sk_sleep(sk), &wait);
>> +
>> +		if (ready < 0) {
>> +			err = -ENOMEM;
>> +			goto out;
>> +		}
>> +
>> +		if (dequeued_total == 0) {
>> +			record_len =
>> +				transport->seqpacket_seq_get_len(vsk);
>> +
>> +			if (record_len == 0)
>> +				continue;
>> +		}
>> +
>> +		/* 'msg_iter.count' is number of unused bytes in iov.
>> +		 * On every copy to iov iterator it is decremented at
>> +		 * size of data.
>> +		 */
>> +		dequeued = transport->seqpacket_dequeue(vsk, msg,
>> +					msg->msg_iter.count, flags);
>                                          ^
>                                          Is this needed or 'msg' can be 
>                                          used in the transport?
Yes, right
>> +
>> +		if (dequeued < 0) {
>> +			dequeued_total = 0;
>> +
>> +			if (dequeued == -EAGAIN) {
>> +				iov_iter_init(&msg->msg_iter, READ,
>> +					      orig_iov, orig_nr_segs,
>> +					      len);
>> +				msg->msg_flags &= ~MSG_EOR;
>> +				continue;
> Why we need to reset MSG_EOR here?

Because if previous attempt to receive record was failed, but

MSG_EOR was set, so we clear it for next attempt to get record

>
>> +			}
>> +
>> +			err = -ENOMEM;
>> +			break;
>> +		}
>> +
>> +		dequeued_total += dequeued;
>> +
>> +		if (dequeued_total >= record_len)
>> +			break;
>> +	}
> Maybe a new line here.
>
>> +	if (sk->sk_err)
>> +		err = -sk->sk_err;
>> +	else if (sk->sk_shutdown & RCV_SHUTDOWN)
>> +		err = 0;
>> +
>> +	if (dequeued_total > 0) {
>> +		/* User sets MSG_TRUNC, so return real length of
>> +		 * packet.
>> +		 */
>> +		if (flags & MSG_TRUNC)
>> +			err = record_len;
>> +		else
>> +			err = len - msg->msg_iter.count;
>> +
>> +		/* Always set MSG_TRUNC if real length of packet is
>> +		 * bigger that user buffer.
> s/that/than
>
>> +		 */
>> +		if (record_len > len)
>> +			msg->msg_flags |= MSG_TRUNC;
>> +	}
>> +out:
>> +	return err;
>> }
>>
>> static int
>> -- 
>> 2.25.1
>>
>