From b472cf36a65c3a7eeb17c3860ecead85e67e56cd Mon Sep 17 00:00:00 2001
From: Joseph Hwang <josephsih@chromium.org>
Date: Fri, 23 Jan 2015 16:22:16 +0800
Subject: [PATCH] add grab flag

This patch grabs the device when --grab command line option is
present. In this way, no other processes are able to access the
device.

TEST=Check that the cursor is frozen when --grab option is specified.
$ evtest --grab
---
 evtest.c   | 38 +++++++++++++++++++++++++++++++++++---
 evtest.txt |  6 +++++-
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/evtest.c b/evtest.c
index 74230ea..6a2b7a1 100644
--- a/evtest.c
+++ b/evtest.c
@@ -55,6 +55,10 @@
 #include <errno.h>
 #include <getopt.h>
 #include <ctype.h>
+#include <signal.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #define BITS_PER_LONG (sizeof(long) * 8)
 #define NBITS(x) ((((x)-1)/BITS_PER_LONG)+1)
@@ -93,6 +97,17 @@ static const struct query_mode {
 	{ "EV_SW",  EV_SW, SW_MAX, EVIOCGSW(SW_MAX) },
 };
 
+static int grab_flag = 0;
+static volatile int stop = 0;
+
+/**
+ * An interrupt handler to ungrab the device.
+ */
+static void interrupt_handler(void)
+{
+	stop = 1;
+}
+
 /**
  * Look up an entry in the query_modes table by its textual name.
  *
@@ -675,8 +690,9 @@ static int version(void)
 static int usage(void)
 {
 	printf("USAGE:\n");
-	printf(" Grab mode:\n");
-	printf("   %s /dev/input/eventX\n", program_invocation_short_name);
+	printf(" Capture mode:\n");
+	printf("   %s [--grab] /dev/input/eventX\n", program_invocation_short_name);
+	printf("     --grab  grab the device for exclusive access\n");
 	printf("\n");
 	printf(" Query mode: (check exit code)\n");
 	printf("   %s --query /dev/input/eventX <type> <value>\n",
@@ -768,8 +784,15 @@ static int print_events(int fd)
 {
 	struct input_event ev[64];
 	int i, rd;
+	fd_set rdfs;
+
+	FD_ZERO(&rdfs);
+	FD_SET(fd, &rdfs);
 
 	while (1) {
+		select(fd + 1, &rdfs, NULL, NULL, NULL);
+		if (stop)
+			break;
 		rd = read(fd, ev, sizeof(struct input_event) * 64);
 
 		if (rd < (int) sizeof(struct input_event)) {
@@ -800,6 +823,9 @@ static int print_events(int fd)
 		}
 
 	}
+
+	ioctl(fd, EVIOCGRAB, (void*)0);
+	return EXIT_SUCCESS;
 }
 
 /**
@@ -814,7 +840,7 @@ static int test_grab(int fd)
 
 	rc = ioctl(fd, EVIOCGRAB, (void*)1);
 
-	if (!rc)
+	if (!rc && !grab_flag)
 		ioctl(fd, EVIOCGRAB, (void*)0);
 
 	return rc;
@@ -878,6 +904,9 @@ static int do_capture(const char *device)
 		printf("***********************************************\n");
 	}
 
+	signal(SIGINT, interrupt_handler);
+	signal(SIGTERM, interrupt_handler);
+
 	return print_events(fd);
 }
 
@@ -954,6 +983,7 @@ static int do_query(const char *device, const char *event_type, const char *keyn
 }
 
 static const struct option long_options[] = {
+	{ "grab", no_argument, &grab_flag, 1 },
 	{ "query", no_argument, NULL, MODE_QUERY },
 	{ "version", no_argument, NULL, MODE_VERSION },
 	{ 0, },
@@ -972,6 +1002,8 @@ int main (int argc, char **argv)
 		if (c == -1)
 			break;
 		switch (c) {
+		case 0:
+			break;
 		case MODE_QUERY:
 			mode = c;
 			break;
diff --git a/evtest.txt b/evtest.txt
index b614482..0a8d3cb 100644
--- a/evtest.txt
+++ b/evtest.txt
@@ -8,7 +8,7 @@ NAME
 
 SYNOPSIS
 --------
-     evtest /dev/input/eventX
+     evtest [--grab] /dev/input/eventX
 
      evtest --query /dev/input/eventX <type> <value>
 
@@ -19,6 +19,10 @@ display information about the specified input device, including all the events
 supported by the device. It then monitors the device and displays all the
 events layer events generated.
 
+If the grab flag is specified in the capture mode, evtest would grab
+the device for exclusive access during its execution period. No other
+processes are allowed to access the device simultaneously in this case.
+
 In the second invocation type ("query mode"), evtest performs a one-shot query
 of the state of a specific key *value* of an event *type*.
 
-- 
2.2.0.rc0.207.ga3a616c