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diff --git a/include/uapi/linux/um_timetravel.h b/include/uapi/linux/um_timetravel.h
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+++ b/include/uapi/linux/um_timetravel.h
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+/*
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Copyright (C) 2019 Intel Corporation
+ */
+#ifndef _UAPI_LINUX_UM_TIMETRAVEL_H
+#define _UAPI_LINUX_UM_TIMETRAVEL_H
+#include <linux/types.h>
+
+/**
+ * struct um_timetravel_msg - UM time travel message
+ *
+ * This is the basic message type, going in both directions.
+ *
+ * This is the message passed between the host (user-mode Linux instance)
+ * and the calendar (the application on the other side of the socket) in
+ * order to implement common scheduling.
+ *
+ * Whenever UML has an event it will request runtime for it from the
+ * calendar, and then wait for its turn until it can run, etc. Note
+ * that it will only ever request the single next runtime, i.e. multiple
+ * REQUEST messages override each other.
+ */
+struct um_timetravel_msg {
+	/**
+	 * @op: operation value from &enum um_timetravel_ops
+	 */
+	__u32 op;
+
+	/**
+	 * @seq: sequence number for the message - shall be reflected in
+	 *	the ACK response, and should be checked while processing
+	 *	the response to see if it matches
+	 */
+	__u32 seq;
+
+	/**
+	 * @time: time in nanoseconds
+	 */
+	__u64 time;
+};
+
+/**
+ * enum um_timetravel_ops - Operation codes
+ */
+enum um_timetravel_ops {
+	/**
+	 * @UM_TIMETRAVEL_ACK: response (ACK) to any previous message,
+	 *	this usually doesn't carry any data in the 'time' field
+	 *	unless otherwise specified below
+	 */
+	UM_TIMETRAVEL_ACK		= 0,
+
+	/**
+	 * @UM_TIMETRAVEL_START: initialize the connection, the time
+	 *	field contains an (arbitrary) ID to possibly be able
+	 *	to distinguish the connections.
+	 */
+	UM_TIMETRAVEL_START		= 1,
+
+	/**
+	 * @UM_TIMETRAVEL_REQUEST: request to run at the given time
+	 *	(host -> calendar)
+	 */
+	UM_TIMETRAVEL_REQUEST		= 2,
+
+	/**
+	 * @UM_TIMETRAVEL_WAIT: Indicate waiting for the previously requested
+	 *	runtime, new requests may be made while waiting (e.g. due to
+	 *	interrupts); the time field is ignored. The calendar must process
+	 *	this message and later	send a %UM_TIMETRAVEL_RUN message when
+	 *	the host can run again.
+	 *	(host -> calendar)
+	 */
+	UM_TIMETRAVEL_WAIT		= 3,
+
+	/**
+	 * @UM_TIMETRAVEL_GET: return the current time from the calendar in the
+	 *	ACK message, the time in the request message is ignored
+	 *	(host -> calendar)
+	 */
+	UM_TIMETRAVEL_GET		= 4,
+
+	/**
+	 * @UM_TIMETRAVEL_UPDATE: time update to the calendar, must be sent e.g.
+	 *	before kicking an interrupt to another calendar
+	 *	(host -> calendar)
+	 */
+	UM_TIMETRAVEL_UPDATE		= 5,
+
+	/**
+	 * @UM_TIMETRAVEL_RUN: run time request granted, current time is in
+	 *	the time field
+	 *	(calendar -> host)
+	 */
+	UM_TIMETRAVEL_RUN		= 6,
+
+	/**
+	 * @UM_TIMETRAVEL_FREE_UNTIL: Enable free-running until the given time,
+	 *	this is a message from the calendar telling the host that it can
+	 *	freely do its own scheduling for anything before the indicated
+	 *	time.
+	 *	Note that if a calendar sends this message once, the host may
+	 *	assume that it will also do so in the future, if it implements
+	 *	wraparound semantics for the time field.
+	 *	(calendar -> host)
+	 */
+	UM_TIMETRAVEL_FREE_UNTIL	= 7,
+
+	/**
+	 * @UM_TIMETRAVEL_GET_TOD: Return time of day, typically used once at
+	 *	boot by the virtual machines to get a synchronized time from
+	 *	the simulation.
+	 */
+	UM_TIMETRAVEL_GET_TOD		= 8,
+};
+
+#endif /* _UAPI_LINUX_UM_TIMETRAVEL_H */