linux-kernel - Re: [RFC PATCH v9 04/19] af_vsock: implement SEQPACKET receive loop

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Date:   Thu, 13 May 2021 17:41:07 +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 v9 04/19] af_vsock: implement SEQPACKET receive loop


On 13.05.2021 14:37, Stefano Garzarella wrote:
> On Sat, May 08, 2021 at 07:33:14PM +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>
>> ---
>> v8 -> v9:
>> 1) 'tmp_record_len' renamed to 'fragment_len'.
>> 2) MSG_TRUNC handled in af_vsock.c instead of transport.
>> 3) 'flags' still passed to transport for MSG_PEEK support.
> Ah, right I see, sorry for the wrong suggestion to remove it.
>
>> include/net/af_vsock.h   |  4 +++
>> net/vmw_vsock/af_vsock.c | 72 +++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 75 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..78b9af545ca8 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -1974,6 +1974,73 @@ 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 fragment_len;
>> +
>> +		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;
>> +		}
>> +
>> +		fragment_len = transport->seqpacket_dequeue(vsk, msg, flags, &msg_ready);
>> +
> So, IIUC, seqpacket_dequeue() must return the real length,
> and not the bytes copied, right?
>
> I'm not sure virtio_transport_seqpacket_do_dequeue() is doing that.
> I'll post a comment on that patch.
Ok, i'll check it
>
>> +		if (fragment_len < 0) {
>> +			err = -ENOMEM;
>> +			break;
>> +		}
>> +
>> +		record_len += fragment_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) {
>> +		/* User sets MSG_TRUNC, so return real length of
>> +		 * packet.
>> +		 */
>> +		if (flags & MSG_TRUNC)
>> +			err = record_len;
>> +		else
>> +			err = len - msg->msg_iter.count;
> I think is better to use msg_data_left(msg) instead of accessing fields.
Ack
>
>> +
>> +		/* Always set MSG_TRUNC if real length of packet is
>> +		 * bigger than user's buffer.
>> +		 */
>> +		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 +2096,10 @@ 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
>>
>