Re: [RFC PATCH v7 11/22] virtio/vsock: dequeue callback for SOCK_SEQPACKET

[Arseny Krasnov]

On 25.03.2021 12:56, Stefano Garzarella wrote:
> On Tue, Mar 23, 2021 at 04:12:41PM +0300, Arseny Krasnov wrote:
>> This adds transport callback and it's logic for SEQPACKET dequeue.
>> Callback fetches RW packets from rx queue of socket until whole record
>> is copied(if user's buffer is full, user is not woken up). This is done
>> to not stall sender, because if we wake up user and it leaves syscall,
>> nobody will send credit update for rest of record, and sender will wait
>> for next enter of read syscall at receiver's side. So if user buffer is
>> full, we just send credit update and drop data. If during copy SEQ_BEGIN
>> was found(and not all data was copied), copying is restarted by reset
>> user's iov iterator(previous unfinished data is dropped).
>>
>> Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
>> ---
>> v6 -> v7:
>> 1) 'struct virtio_vsock_seqpacket_state' now renamed to
>>    'struct virtio_vsock_seq_state'.
>> 2) Field 'seqpacket_state' of 'struct virtio_vsock_sock' now
>>    renamed to 'seq_state'.
>> 3) Current message length to process('user_read_seq_len') is
>>    set to 0 on error or message dequeue completed sucecssfully.
>>
>> include/linux/virtio_vsock.h            |  14 +++
>> include/uapi/linux/virtio_vsock.h       |  16 ++++
>> net/vmw_vsock/virtio_transport_common.c | 121 ++++++++++++++++++++++++
>> 3 files changed, 151 insertions(+)
>>
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index dc636b727179..0e3aa395c07c 100644
>> --- a/include/linux/virtio_vsock.h
>> +++ b/include/linux/virtio_vsock.h
>> @@ -18,6 +18,12 @@ enum {
>> 	VSOCK_VQ_MAX    = 3,
>> };
>>
>> +struct virtio_vsock_seq_state {
>> +	u32 user_read_seq_len;
>> +	u32 user_read_copied;
>> +	u32 curr_rx_msg_id;
>> +};
>> +
>> /* Per-socket state (accessed via vsk->trans) */
>> struct virtio_vsock_sock {
>> 	struct vsock_sock *vsk;
>> @@ -36,6 +42,8 @@ struct virtio_vsock_sock {
>> 	u32 rx_bytes;
>> 	u32 buf_alloc;
>> 	struct list_head rx_queue;
>> +
>> +	struct virtio_vsock_seq_state seq_state;
>> };
>>
>> struct virtio_vsock_pkt {
>> @@ -80,6 +88,12 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>> 			       struct msghdr *msg,
>> 			       size_t len, int flags);
>>
>> +int
>> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
>> +				   struct msghdr *msg,
>> +				   int flags,
>> +				   bool *msg_ready,
>> +				   size_t *msg_len);
>> s64 virtio_transport_stream_has_data(struct vsock_sock *vsk);
>> s64 virtio_transport_stream_has_space(struct vsock_sock *vsk);
>>
>> diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>> index 1d57ed3d84d2..692f8078cced 100644
>> --- a/include/uapi/linux/virtio_vsock.h
>> +++ b/include/uapi/linux/virtio_vsock.h
> Maybe we can move the following changes to this file (that should match 
> the virtio-spec discussed in the separate thread) in a separate patch 
> with a reference to the spec.
>
> You can include this in the series before this patch.
Ack
>
>> @@ -63,8 +63,14 @@ struct virtio_vsock_hdr {
>> 	__le32	fwd_cnt;
>> } __attribute__((packed));
>>
>> +struct virtio_vsock_seq_hdr {
>> +	__le32  msg_id;
>> +	__le32  msg_len;
>> +} __attribute__((packed));
>> +
>> enum virtio_vsock_type {
>> 	VIRTIO_VSOCK_TYPE_STREAM = 1,
>> +	VIRTIO_VSOCK_TYPE_SEQPACKET = 2,
>> };
>>
>> enum virtio_vsock_op {
>> @@ -83,6 +89,11 @@ enum virtio_vsock_op {
>> 	VIRTIO_VSOCK_OP_CREDIT_UPDATE = 6,
>> 	/* Request the peer to send the credit info to us */
>> 	VIRTIO_VSOCK_OP_CREDIT_REQUEST = 7,
>> +
>> +	/* Record begin for SOCK_SEQPACKET */
>> +	VIRTIO_VSOCK_OP_SEQ_BEGIN = 8,
>> +	/* Record end for SOCK_SEQPACKET */
>> +	VIRTIO_VSOCK_OP_SEQ_END = 9,
>> };
>>
>> /* VIRTIO_VSOCK_OP_SHUTDOWN flags values */
>> @@ -91,4 +102,9 @@ enum virtio_vsock_shutdown {
>> 	VIRTIO_VSOCK_SHUTDOWN_SEND = 2,
>> };
>>
>> +/* VIRTIO_VSOCK_OP_RW flags values */
>> +enum virtio_vsock_rw {
>> +	VIRTIO_VSOCK_RW_EOR = 1,
>> +};
>> +
>> #endif /* _UAPI_LINUX_VIRTIO_VSOCK_H */
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 833104b71a1c..a8f4326e45e8 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -393,6 +393,114 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
>> 	return err;
>> }
>>
>> +static inline void virtio_transport_remove_pkt(struct virtio_vsock_pkt *pkt)
>> +{
>> +	list_del(&pkt->list);
>> +	virtio_transport_free_pkt(pkt);
>> +}
>> +
>> +static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
>> +						 struct msghdr *msg,
>> +						 bool *msg_ready)
>> +{
>> +	struct virtio_vsock_sock *vvs = vsk->trans;
>> +	struct virtio_vsock_pkt *pkt;
>> +	int err = 0;
>> +	size_t user_buf_len = msg->msg_iter.count;
>> +
>> +	*msg_ready = false;
>> +	spin_lock_bh(&vvs->rx_lock);
>> +
>> +	while (!*msg_ready && !list_empty(&vvs->rx_queue) && !err) {
>> +		pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
>> +
>> +		switch (le16_to_cpu(pkt->hdr.op)) {
>> +		case VIRTIO_VSOCK_OP_SEQ_BEGIN: {
>> +			/* Unexpected 'SEQ_BEGIN' during record copy:
>> +			 * Leave receive loop, 'EAGAIN' will restart it from
>> +			 * outer receive loop, packet is still in queue and
>> +			 * counters are cleared. So in next loop enter,
>> +			 * 'SEQ_BEGIN' will be dequeued first. User's iov
>> +			 * iterator will be reset in outer loop. Also
>> +			 * send credit update, because some bytes could be
>> +			 * copied. User will never see unfinished record.
>> +			 */
>> +			err = -EAGAIN;
>> +			break;
>> +		}
>> +		case VIRTIO_VSOCK_OP_SEQ_END: {
>> +			struct virtio_vsock_seq_hdr *seq_hdr;
>> +
>> +			seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
>> +			/* First check that whole record is received. */
>> +
>> +			if (vvs->seq_state.user_read_copied !=
>> +			    vvs->seq_state.user_read_seq_len ||
>> +			    le32_to_cpu(seq_hdr->msg_id) !=
>> +			    vvs->seq_state.curr_rx_msg_id) {
>> +				/* Tail of current record and head of 
>> next missed,
>> +				 * so this EOR is from next record. Restart receive.
>> +				 * Current record will be dropped, next headless will
>> +				 * be dropped on next attempt to get record length.
>> +				 */
>> +				err = -EAGAIN;
>> +			} else {
>> +				/* Success. */
>> +				*msg_ready = true;
>> +			}
>> +
>> +			break;
>> +		}
>> +		case VIRTIO_VSOCK_OP_RW: {
>> +			size_t bytes_to_copy;
>> +			size_t pkt_len;
>> +
>> +			pkt_len = (size_t)le32_to_cpu(pkt->hdr.len);
>> +			bytes_to_copy = min(user_buf_len, pkt_len);
>> +
>> +			/* sk_lock is held by caller so no one else can dequeue.
>> +			 * Unlock rx_lock since memcpy_to_msg() may sleep.
>> +			 */
>> +			spin_unlock_bh(&vvs->rx_lock);
>> +
>> +			if (memcpy_to_msg(msg, pkt->buf, bytes_to_copy)) {
>> +				spin_lock_bh(&vvs->rx_lock);
>> +				err = -EINVAL;
>> +				break;
>> +			}
>> +
>> +			spin_lock_bh(&vvs->rx_lock);
>> +			user_buf_len -= bytes_to_copy;
>> +			vvs->seq_state.user_read_copied += pkt_len;
>> +
>> +			if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_RW_EOR)
>> +				msg->msg_flags |= MSG_EOR;
>> +			break;
>> +		}
>> +		default:
>> +			;
>> +		}
>> +
>> +		/* For unexpected 'SEQ_BEGIN', keep such packet in queue,
>> +		 * but drop any other type of packet.
>> +		 */
>> +		if (le16_to_cpu(pkt->hdr.op) != VIRTIO_VSOCK_OP_SEQ_BEGIN) {
>> +			virtio_transport_dec_rx_pkt(vvs, pkt);
>> +			virtio_transport_remove_pkt(pkt);
>> +		}
>> +	}
>> +
>> +	/* Reset current record length on error or whole message received. */
>> +	if (*msg_ready || err)
>> +		vvs->seq_state.user_read_seq_len = 0;
>> +
>> +	spin_unlock_bh(&vvs->rx_lock);
>> +
>> +	virtio_transport_send_credit_update(vsk);
>> +
>> +	return err;
>> +}
>> +
>> ssize_t
>> virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>> 				struct msghdr *msg,
>> @@ -405,6 +513,19 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>> }
>> EXPORT_SYMBOL_GPL(virtio_transport_stream_dequeue);
>>
>> +int
>> +virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
>> +				   struct msghdr *msg,
>> +				   int flags, bool *msg_ready,
>> +				   size_t *msg_len)
>> +{
>> +	if (flags & MSG_PEEK)
>> +		return -EOPNOTSUPP;
>> +
> msg_len seems not filled...
>
>
>> +	return virtio_transport_seqpacket_do_dequeue(vsk, msg, 
>> msg_ready);
>> +}
>> +EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
>> +
>> int
>> virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
>> 			       struct msghdr *msg,
>> -- 
>> 2.25.1
>>
>