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

Arseny Krasnov
2021-04-21T14:48:34Z

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@kaspersky.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
>>
>