no-fork option for tapdisk2 debugging.

To simplify running tapdisk2 from a debugger, add an opttion "-n" to disable foring into the background.

Signed-off-by: Philipp Hahn <hahn@xxxxxxxxxxxxx>
--
[v2] fold extra indention patch into patch.
--- xen-4.0.1.orig/tools/blktap2/drivers/tapdisk2.c	2010-08-25 12:22:07.000000000 +0200
+++ xen-4.0.1/tools/blktap2/drivers/tapdisk2.c	2011-06-17 17:37:35.000000000 +0200
@@ -402,7 +402,7 @@ tapdisk2_wait_for_device(void)
 static void
 usage(const char *app, int err)
 {
-	fprintf(stderr, "usage: %s <-n file>\n", app);
+	fprintf(stderr, "usage: %s [-f] -n driver:file\n", app);
 	exit(err);
 }
 
@@ -411,10 +411,11 @@ main(int argc, char *argv[])
 {
 	int c;
 	char *params;
+	int do_fork = 1;
 
 	params = NULL;
 
-	while ((c = getopt(argc, argv, "n:s:h")) != -1) {
+	while ((c = getopt(argc, argv, "n:s:fh")) != -1) {
 		switch (c) {
 		case 'n':
 			params = optarg;
@@ -430,6 +431,9 @@ main(int argc, char *argv[])
 			exit(EXIT_FAILURE);
 #endif
 			break;
+		case 'f':
+			do_fork = 0;
+			break;
 		default:
 			usage(argv[0], EINVAL);
 		}
@@ -438,12 +442,17 @@ main(int argc, char *argv[])
 	if (!params || optind != argc)
 		usage(argv[0], EINVAL);
 
-	if (pipe(channel) == -1) {
-		printf("pipe failed: %d\n", errno);
-		return errno;
-	}
+	if (do_fork) {
+		if (pipe(channel) == -1) {
+			printf("pipe failed: %d\n", errno);
+			return errno;
+		}
+	} else {
+		channel[0] = dup(STDIN_FILENO);
+		channel[1] = dup(STDERR_FILENO);
+	}
 
-	switch (fork()) {
+	switch (do_fork ? fork() : 0) {
 	case -1:
 		printf("fork failed: %d\n", errno);
 		return errno;