linux-kernel - Re: [RFC PATCH v8 04/19] af_vsock: implement SEQPACKET receive loop

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Date:   Wed, 21 Apr 2021 17:47:44 +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 v8 04/19] af_vsock: implement SEQPACKET receive loop


On 21.04.2021 11:37, Stefano Garzarella wrote:
> On Tue, Apr 13, 2021 at 03:42:47PM +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>
>> ---
>> v7 -> v8:
>> - Length of message is now not returned by callback, it returns only
>>   length of data read by each call.
>> - Previous case, when EAGAIN is return and dequeue loop restarted now
>>   removed(in this simplified version we consider that message could not
>>   be corrupted).
>> - MSG_TRUNC in input flags is now handled by callback.
>>
>> include/net/af_vsock.h   |  4 +++
>> net/vmw_vsock/af_vsock.c | 66 +++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 69 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> index b1c717286993..5175f5a52ce1 100644
>> --- a/include/net/af_vsock.h
>> +++ b/include/net/af_vsock.h
>> @@ -135,6 +135,10 @@ struct vsock_transport {
>> 	bool (*stream_is_active)(struct vsock_sock *);
>> 	bool (*stream_allow)(u32 cid, u32 port);
>>
>> +	/* SEQ_PACKET. */
>> +	ssize_t (*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 c4f6bfa1e381..d9fb4f9a3063 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -1974,6 +1974,67 @@ 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;
>> +	bool msg_ready;
>> +	struct vsock_sock *vsk;
>> +	ssize_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_ready = false;
>> +	record_len = 0;
>> +
>> +	while (1) {
>> +		ssize_t tmp_record_len;
> Maybe better a name like `partial_len`, `fragment_len`, or just `read`.
Ack
>
>> +
>> +		if (vsock_wait_data(sk, &wait, timeout, NULL, 0) <= 0) {
>> +			/* In case of any loop break(timeout, signal
>> +			 * interrupt or shutdown), we report user that
>> +			 * nothing was copied.
>> +			 */
>> +			err = 0;
>> +			break;
>> +		}
>> +
>> +		tmp_record_len = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready);
> I think we can avoid to pass 'flags' down to the transports.
>
> We can require that seqpacket_dequeue() should always return the real 
> size of the packet received, and then check below if 'MSG_TRUNC' was 
> set...
Ack
>
>> +
>> +		if (tmp_record_len < 0) {
>> +			err = -ENOMEM;
>> +			break;
>> +		}
>> +
>> +		record_len += tmp_record_len;
>> +
>> +		if (msg_ready)
>> +			break;
>> +	}
>> +
>> +	if (sk->sk_err)
>> +		err = -sk->sk_err;
>> +	else if (sk->sk_shutdown & RCV_SHUTDOWN)
>> +		err = 0;
>> +
>> +	if (msg_ready && err == 0) {
>> +		err = record_len;
>> +
>> +		/* Always set MSG_TRUNC if real length of packet is
>> +		 * bigger than user's buffer.
>> +		 */
> ...here:
> 		if (flags & MSG_TRUNC && record_len > len)
>
>> +		if (record_len > len)
>> +			msg->msg_flags |= MSG_TRUNC;
>> +	}
>> +
>> +	return err;
>> +}
>> +
>> static int
>> vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>> 			  int flags)
>> @@ -2029,7 +2090,10 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>> 		goto out;
>> 	}
>>
>> -	err = __vsock_stream_recvmsg(sk, msg, len, flags);
>> +	if (sk->sk_type == SOCK_STREAM)
>> +		err = __vsock_stream_recvmsg(sk, msg, len, flags);
>> +	else
>> +		err = __vsock_seqpacket_recvmsg(sk, msg, len, flags);
>>
>> out:
>> 	release_sock(sk);
>> -- )
>> 2.25.1
>>
>