A few reliability improvements in the power management interface

Nathanael Rensen <nathanael at list ! polymorpheus ! com> came up with
a few improvements to the event watcher and power management interface,
namely:

 o Make sure to put our watcher on a list before issuing an XS_WATCH
   command since Xen will raise the event right after it's been set up.

 o The first time xen_control is called the "control/shutdown" node
   may not exist, so skip printing the error message in this case.

 o Acknowledge requests by writing back an empty string.

 o log(9) reboot and halt requests like vmt(4) does.

Huge thanks!

3 files changed, 43 insertions, 19 deletions

diff --git a/sys/dev/pv/xen.c b/sys/dev/pv/xen.c
index 8aa7565cba8..5770d897ceb 100644
--- a/sys/dev/pv/xen.c
+++ b/sys/dev/pv/xen.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: xen.c,v 1.48 2016/01/29 19:12:26 mikeb Exp $	*/
+/*	$OpenBSD: xen.c,v 1.49 2016/02/02 17:52:46 mikeb Exp $	*/
 
 /*
  * Copyright (c) 2015 Mike Belopuhov
@@ -25,6 +25,7 @@
 #include <sys/kernel.h>
 #include <sys/device.h>
 #include <sys/task.h>
+#include <sys/syslog.h>
 
 #include <machine/bus.h>
 #include <machine/cpu.h>
@@ -34,6 +35,8 @@
 
 #include <machine/i82489var.h>
 
+#include <dev/rndvar.h>
+
 #include <dev/pv/pvvar.h>
 #include <dev/pv/pvreg.h>
 #include <dev/pv/xenreg.h>
@@ -193,34 +196,48 @@ xen_control(void *arg)
 	struct xen_softc *sc = arg;
 	struct xs_transaction xst;
 	char action[128];
+	int error;
 
 	memset(&xst, 0, sizeof(xst));
 	xst.xst_id = 0;
 	xst.xst_sc = sc->sc_xs;
 
-	if (xs_getprop(sc, "control", "shutdown", action, sizeof(action))) {
-		printf("%s: failed to process control event\n",
-		    sc->sc_dev.dv_xname);
+	error = xs_getprop(sc, "control", "shutdown", action, sizeof(action));
+	if (error) {
+		if (error != ENOENT)
+			printf("%s: failed to process control event\n",
+			    sc->sc_dev.dv_xname);
 		return;
 	}
 
 	if (strlen(action) == 0)
 		return;
 
+	/* Acknowledge the event */
+	xs_setprop(sc, "control", "shutdown", "", 0);
+
 	if (strcmp(action, "halt") == 0 || strcmp(action, "poweroff") == 0) {
 		extern int allowpowerdown;
 
-		if (allowpowerdown == 1) {
-			allowpowerdown = 0;
-			prsignal(initprocess, SIGUSR2);
-		}
+		if (allowpowerdown == 0)
+			return;
+
+		suspend_randomness();
+
+		log(LOG_KERN | LOG_NOTICE, "Shutting down in response to "
+		    "request from Xen host\n");
+		prsignal(initprocess, SIGUSR2);
 	} else if (strcmp(action, "reboot") == 0) {
 		extern int allowpowerdown;
 
-		if (allowpowerdown == 1) {
-			allowpowerdown = 0;
-			prsignal(initprocess, SIGINT);
-		}
+		if (allowpowerdown == 0)
+			return;
+
+		suspend_randomness();
+
+		log(LOG_KERN | LOG_NOTICE, "Rebooting in response to request "
+		    "from Xen host\n");
+		prsignal(initprocess, SIGINT);
 	} else if (strcmp(action, "crash") == 0) {
 		panic("xen told us to do this");
 	} else if (strcmp(action, "suspend") == 0) {
diff --git a/sys/dev/pv/xenstore.c b/sys/dev/pv/xenstore.c
index c1262cf9590..95b1fdc7fa2 100644
--- a/sys/dev/pv/xenstore.c
+++ b/sys/dev/pv/xenstore.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: xenstore.c,v 1.24 2016/01/29 19:04:30 mikeb Exp $	*/
+/*	$OpenBSD: xenstore.c,v 1.25 2016/02/02 17:52:46 mikeb Exp $	*/
 
 /*
  * Copyright (c) 2015 Mike Belopuhov
@@ -850,15 +850,22 @@ xs_watch(struct xen_softc *sc, const char *path, const char *property,
 	iov.iov_len = sizeof(xsw->xsw_token);
 	iov_cnt = 1;
 
+	/*
+	 * xs_watches must be prepared pre-emptively because a xenstore
+	 * event is raised immediately after a watch is established.
+	 */
+	mtx_enter(&xs->xs_watchlck);
+	TAILQ_INSERT_TAIL(&xs->xs_watches, xsw, xsw_entry);
+	mtx_leave(&xs->xs_watchlck);
+
 	if ((error = xs_cmd(&xst, XS_WATCH, key, &iovp, &iov_cnt)) != 0) {
+		mtx_enter(&xs->xs_watchlck);
+		TAILQ_REMOVE(&xs->xs_watches, xsw, xsw_entry);
+		mtx_leave(&xs->xs_watchlck);
 		free(xsw, M_DEVBUF, sizeof(*xsw));
 		return (error);
 	}
 
-	mtx_enter(&xs->xs_watchlck);
-	TAILQ_INSERT_TAIL(&xs->xs_watches, xsw, xsw_entry);
-	mtx_leave(&xs->xs_watchlck);
-
 	return (0);
 }
 
diff --git a/sys/dev/pv/xenvar.h b/sys/dev/pv/xenvar.h
index 29c013d2ad0..34f381b78a7 100644
--- a/sys/dev/pv/xenvar.h
+++ b/sys/dev/pv/xenvar.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: xenvar.h,v 1.28 2016/01/29 19:12:26 mikeb Exp $	*/
+/*	$OpenBSD: xenvar.h,v 1.29 2016/02/02 17:52:46 mikeb Exp $	*/
 
 /*
  * Copyright (c) 2015 Mike Belopuhov
@@ -19,7 +19,7 @@
 #ifndef _XENVAR_H_
 #define _XENVAR_H_
 
-#define XEN_DEBUG
+/* #define XEN_DEBUG */
 
 #ifdef XEN_DEBUG
 #define DPRINTF(x...)		printf(x)