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

Arseny Krasnov
2021-01-29T06:30:35Z

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

>
>> + }
>> +
>> + 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
>>
>