Re: [RFC PATCH v2 08/13] virtio/vsock: dequeue callback for SOCK_SEQPACKET.

[Stefano Garzarella <sgarzare@redhat.com>]

On Fri, Jan 15, 2021 at 08:43:24AM +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@kaspersky.com>
>---
> include/linux/virtio_vsock.h            |   4 +
> include/uapi/linux/virtio_vsock.h       |   9 ++
> net/vmw_vsock/virtio_transport_common.c | 128 ++++++++++++++++++++++++
> 3 files changed, 141 insertions(+)
>
>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>index dc636b727179..7f0ef5204e33 100644
>--- a/include/linux/virtio_vsock.h
>+++ b/include/linux/virtio_vsock.h
>@@ -36,6 +36,10 @@ struct virtio_vsock_sock {
> 	u32 rx_bytes;
> 	u32 buf_alloc;
> 	struct list_head rx_queue;
>+
>+	/* For SOCK_SEQPACKET */
>+	u32 user_read_seq_len;
>+	u32 user_read_copied;
> };
>
> struct virtio_vsock_pkt {
>diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>index 1d57ed3d84d2..058908bc19fc 100644
>--- a/include/uapi/linux/virtio_vsock.h
>+++ b/include/uapi/linux/virtio_vsock.h
>@@ -65,6 +65,7 @@ struct virtio_vsock_hdr {
>
> enum virtio_vsock_type {
> 	VIRTIO_VSOCK_TYPE_STREAM = 1,
>+	VIRTIO_VSOCK_TYPE_SEQPACKET = 2,
> };
>
> enum virtio_vsock_op {
>@@ -83,6 +84,9 @@ 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,
> };
>
> /* VIRTIO_VSOCK_OP_SHUTDOWN flags values */
>@@ -91,4 +95,9 @@ enum virtio_vsock_shutdown {
> 	VIRTIO_VSOCK_SHUTDOWN_SEND = 2,
> };
>
>+/* VIRTIO_VSOCK_OP_RW flags values for SOCK_SEQPACKET type */
>+enum virtio_vsock_rw_seqpacket {
>+	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 5956939eebb7..4328f653a477 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -397,6 +397,132 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> 	return err;
> }
>
>+static inline void virtio_transport_del_n_free_pkt(struct virtio_vsock_pkt *pkt)
>+{
>+	list_del(&pkt->list);
>+	virtio_transport_free_pkt(pkt);
>+}
>+
>+static size_t virtio_transport_drop_until_seq_begin(struct virtio_vsock_sock *vvs)
>+{
>+	struct virtio_vsock_pkt *pkt, *n;
>+	size_t bytes_dropped = 0;
>+
>+	list_for_each_entry_safe(pkt, n, &vvs->rx_queue, list) {
>+		if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_SEQ_BEGIN)
>+			break;
>+
>+		bytes_dropped += le32_to_cpu(pkt->hdr.len);
>+		virtio_transport_dec_rx_pkt(vvs, pkt);
>+		virtio_transport_del_n_free_pkt(pkt);
>+	}
>+
>+	return bytes_dropped;
>+}
>+
>+static ssize_t virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
>+						     struct msghdr *msg,
>+						     size_t user_buf_len)
>+{
>+	struct virtio_vsock_sock *vvs = vsk->trans;
>+	struct virtio_vsock_pkt *pkt;
>+	size_t bytes_handled = 0;
>+	int err = 0;
>+
>+	spin_lock_bh(&vvs->rx_lock);
>+
>+	if (user_buf_len == 0) {
>+		/* User's buffer is full, we processing rest of
>+		 * record and drop it. If 'SEQ_BEGIN' is found
>+		 * while iterating, user will be woken up,
>+		 * because record is already copied, and we
>+		 * don't care about absent of some tail RW packets
>+		 * of it. Return number of bytes(rest of record),
>+		 * but ignore credit update for such absent bytes.
>+		 */
>+		bytes_handled = virtio_transport_drop_until_seq_begin(vvs);
>+		vvs->user_read_copied += bytes_handled;
>+
>+		if (!list_empty(&vvs->rx_queue) &&
>+		    vvs->user_read_copied < vvs->user_read_seq_len) {
>+			/* 'SEQ_BEGIN' found, but record isn't complete.
>+			 * Set number of copied bytes to fit record size
>+			 * and force counters to finish receiving.
>+			 */
>+			bytes_handled += (vvs->user_read_seq_len - vvs->user_read_copied);
>+			vvs->user_read_copied = vvs->user_read_seq_len;
>+		}
>+	}
>+
>+	/* Now start copying. */
>+	while (vvs->user_read_copied < vvs->user_read_seq_len &&
>+	       vvs->rx_bytes &&
>+	       user_buf_len &&
>+	       !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_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;
>+			bytes_handled += pkt->len;
>+			vvs->user_read_copied += bytes_to_copy;
>+
>+			if (le16_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_RW_EOR)
                             ^
hdr.flags is __le32, so please use le32_to_cpu()

>+				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_del_n_free_pkt(pkt);
>+		}
>+	}
>+
>+	spin_unlock_bh(&vvs->rx_lock);
>+
>+	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_SEQPACKET,
>+					    NULL);
>+
>+	return err ?: bytes_handled;
>+}
>+
> ssize_t
> virtio_transport_stream_dequeue(struct vsock_sock *vsk,
> 				struct msghdr *msg,
>@@ -481,6 +607,8 @@ int virtio_transport_do_socket_init(struct vsock_sock *vsk,
> 	spin_lock_init(&vvs->rx_lock);
> 	spin_lock_init(&vvs->tx_lock);
> 	INIT_LIST_HEAD(&vvs->rx_queue);
>+	vvs->user_read_copied = 0;
>+	vvs->user_read_seq_len = 0;
>
> 	return 0;
> }
>-- 
>2.25.1
>