Re: [RFC PATCH v4 09/17] virtio/vsock: dequeue callback for SOCK_SEQPACKET

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Feb 11, 2021 at 02:54:28PM +0100, Stefano Garzarella wrote:
>On Sun, Feb 07, 2021 at 06:16:46PM +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            |   5 +
>>include/uapi/linux/virtio_vsock.h       |  16 ++++
>>net/vmw_vsock/virtio_transport_common.c | 120 ++++++++++++++++++++++++
>>3 files changed, 141 insertions(+)
>>
>>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>>index dc636b727179..4d0de3dee9a4 100644
>>--- a/include/linux/virtio_vsock.h
>>+++ b/include/linux/virtio_vsock.h
>>@@ -36,6 +36,11 @@ 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;
>>+	u32 curr_rx_msg_cnt;
>>};
>>
>>struct virtio_vsock_pkt {
>>diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>>index 1d57ed3d84d2..cf9c165e5cca 100644
>>--- a/include/uapi/linux/virtio_vsock.h
>>+++ b/include/uapi/linux/virtio_vsock.h
>>@@ -63,8 +63,14 @@ struct virtio_vsock_hdr {
>>	__le32	fwd_cnt;
>>} __attribute__((packed));
>>
>>+struct virtio_vsock_seq_hdr {
>>+	__le32  msg_cnt;

Maybe it's better 'msg_id' for this field, since we use it to identify a 
message. Then whether we use a counter or a random number, I think it's 
just an implementation detail.

As Michael said, perhaps this detail should be discussed in the proposal 
for VIRTIO spec changes.

>>+	__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 5956939eebb7..4572d01c8ea5 100644
>>--- a/net/vmw_vsock/virtio_transport_common.c
>>+++ b/net/vmw_vsock/virtio_transport_common.c
>>@@ -397,6 +397,126 @@ 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 size_t virtio_transport_drop_until_seq_begin(struct virtio_vsock_sock *vvs)
>>+{
>
>This function is not used here, but in the next patch, so I'd add this 
>with the next patch.
>
>>+	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_remove_pkt(pkt);
>>+	}
>>+
>>+	return bytes_dropped;
>>+}
>>+
>>+static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
>>+						 struct msghdr *msg,
>>+						 bool *msg_ready)
>>+{
>
>Also this function is not used, maybe you can add in this patch the 
>virtio_transport_seqpacket_dequeue() implementation.
>
>>+	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->user_read_copied != vvs->user_read_seq_len ||
>>+			    (le32_to_cpu(seq_hdr->msg_cnt) - vvs->curr_rx_msg_cnt) != 1) {
>>+				/* 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->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);
>>+		}
>>+	}
>>+
>>+	spin_unlock_bh(&vvs->rx_lock);
>>+
>>+	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_SEQPACKET,
>>+					    NULL);
>>+
>>+	return err;
>>+}
>>+
>>ssize_t
>>virtio_transport_stream_dequeue(struct vsock_sock *vsk,
>>				struct msghdr *msg,
>>-- 
>>2.25.1
>>