From dd77b90d427f9be31805d9331d3ad18e32d2a2b0 Mon Sep 17 00:00:00 2001
From: Marek Marczykowski <marmarek@invisiblethingslab.com>
Date: Mon, 26 Dec 2011 23:29:07 +0100
Subject: [PATCH] vm: force meminfo-writer to wait for the first user process
 (#392)

meminfo-writer will wait for SIGUSR1 - send by qrexec-agent on the first
qvm-run from dom0.
---
 appvm/qubes_core_appvm  |  2 +-
 common/meminfo-writer.c | 48 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/appvm/qubes_core_appvm b/appvm/qubes_core_appvm
index 085b544..9e0d68c 100755
--- a/appvm/qubes_core_appvm
+++ b/appvm/qubes_core_appvm
@@ -64,7 +64,7 @@ start()
 	if [ "$start_meminfo_writer" != "0" ]; then
 		MEM_CHANGE_THRESHOLD_KB=30000
 		MEMINFO_DELAY_USEC=100000
-		/usr/lib/qubes/meminfo-writer $MEM_CHANGE_THRESHOLD_KB $MEMINFO_DELAY_USEC &
+		/usr/lib/qubes/meminfo-writer $MEM_CHANGE_THRESHOLD_KB $MEMINFO_DELAY_USEC /var/run/meminfo-writer.pid
 	fi
 
 	success
diff --git a/common/meminfo-writer.c b/common/meminfo-writer.c
index 49c8b6a..c9e1059 100644
--- a/common/meminfo-writer.c
+++ b/common/meminfo-writer.c
@@ -5,10 +5,12 @@
 #include <xs.h>
 #include <syslog.h>
 #include <string.h>
+#include <signal.h>
 
 unsigned long prev_used_mem;
 int used_mem_change_threshold;
 int delay;
+int usr1_received;
 
 char *parse(char *buf)
 {
@@ -73,7 +75,10 @@ char *parse(char *buf)
 void usage()
 {
 	fprintf(stderr,
-		"usage: meminfo_writer threshold_in_kb delay_in_us\n");
+		"usage: meminfo_writer threshold_in_kb delay_in_us [pidfile]\n");
+	fprintf(stderr, "  When pidfile set, meminfo-writer will:\n");
+    fprintf(stderr, "   - fork into background\n");
+	fprintf(stderr, "   - wait for SIGURS1 (in background) before starting main work\n");
 	exit(1);
 }
 
@@ -85,6 +90,10 @@ void send_to_qmemman(struct xs_handle *xs, char *data)
 	}
 }
 
+void usr1_handler(int sig) {
+	usr1_received = 1;
+}
+
 int main(int argc, char **argv)
 {
 	char buf[4096];
@@ -93,13 +102,48 @@ int main(int argc, char **argv)
 	int fd;
 	struct xs_handle *xs;
 
-	if (argc != 3)
+	if (argc != 3 && argc != 4)
 		usage();
 	used_mem_change_threshold = atoi(argv[1]);
 	delay = atoi(argv[2]);
 	if (!used_mem_change_threshold || !delay)
 		usage();
 
+	if (argc == 4) {
+		pid_t pid;
+		sigset_t mask, oldmask;
+
+		switch (pid = fork()) {
+			case -1:
+				perror("fork");
+				exit(1);
+			case 0:
+				sigemptyset (&mask); 
+				sigaddset (&mask, SIGUSR1);
+				/* Wait for a signal to arrive. */
+				sigprocmask (SIG_BLOCK, &mask, &oldmask);
+				usr1_received = 0;
+				signal(SIGUSR1, usr1_handler);
+				while (!usr1_received)
+					  sigsuspend (&oldmask);
+				sigprocmask (SIG_UNBLOCK, &mask, NULL);
+				break;
+			default:
+				fd = open(argv[3], O_CREAT | O_TRUNC | O_WRONLY, 0666);
+				if (fd < 0) {
+					perror("open pidfile");
+					exit(1);
+				}
+				n = sprintf(buf, "%d\n", pid);
+				if (write(fd, buf, n) != n) {
+					perror("write pid");
+					exit(1);
+				}
+				close(fd);
+				exit(0);
+		}
+	}
+
 	fd = open("/proc/meminfo", O_RDONLY);
 	if (fd < 0) {
 		perror("open meminfo");