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List:       linux-virtualization
Subject:    Re: [RFC PATCH v3 03/13] af_vsock: implement SEQPACKET rx loop
From:       Stefano Garzarella <sgarzare () redhat ! com>
Date:       2021-01-29 9:21:58
Message-ID: 20210129092158.tm2bdwpqufsneaxw () steredhat
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On Fri, Jan 29, 2021 at 09:28:49AM +0300, Arseny Krasnov wrote:
>
>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@kaspersky.com>
>>> ---
>>> 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

Yes, I saw later when I looked at the implementation in the transport.

Maybe better to put a comment saying that seqpacket_dequeue() can set 
that flag.

Thanks,
Stefano

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