[PATCH user-cr] add -t option to mount new devpts

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Trivial patch, and I'm not sure whether we want this or want to
do it this way.  But it saves me having to do it during my restart.sh
wrapper shell-script.

Signed-off-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 restart.c |   35 ++++++++++++++++++++++++++++++++++-
 1 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/restart.c b/restart.c
index 063e973..03c1850 100644
--- a/restart.c
+++ b/restart.c
@@ -30,6 +30,7 @@
 #include <asm/unistd.h>
 #include <sys/syscall.h>
 #include <sys/prctl.h>
+#include <sys/mount.h>
 
 #include <linux/sched.h>
 #include <linux/checkpoint.h>
@@ -79,6 +80,7 @@ static char usage_str[] =
 "  -l,--logfile=FILE     write error and debug data to FILE (default=none)\n"
 "     --logfile-fd=FD    write error and debug data to file desctiptor FD\n"
 "     --inspect          inspect image on-the-fly for error records\n"
+"  -t,--pty		 start in a new devpts namespace to support ptys\n"
 "  -v,--verbose          verbose output\n"
 "  -d,--debug            debugging output\n"
 "     --warn-COND        warn on condition COND, but proceed anyways\n"
@@ -365,6 +367,7 @@ struct args {
 	long warn;
 	long fail;
 	int keep_lsm;
+	int pty;
 };
 
 #define CKPT_COND_PIDZERO  0x1
@@ -444,9 +447,10 @@ static void parse_args(struct args *args, int argc, char *argv[])
 		{ "debug",	no_argument,		NULL, 'd' },
 		{ "warn-pidzero",	no_argument,	NULL, 9 },
 		{ "fail-pidzero",	no_argument,	NULL, 10 },
+		{ "pty", no_argument,			NULL, 't'},
 		{ NULL,		0,			NULL, 0 }
 	};
-	static char optc[] = "hdvkpPwWF:r:i:l:";
+	static char optc[] = "hdvkpPwWF:r:i:l:t";
 
 	int optind;
 	int sig;
@@ -456,6 +460,7 @@ static void parse_args(struct args *args, int argc, char *argv[])
 	args->wait = 1;
 	args->infd = -1;
 	args->logfd = -1;
+	args->pty = 0;
 
 	while (1) {
 		int c = getopt_long(argc, argv, optc, opts, &optind);
@@ -469,6 +474,9 @@ static void parse_args(struct args *args, int argc, char *argv[])
 		case 'v':
 			global_verbose = 1;
 			break;
+		case 't':
+			args->pty = 1;
+			break;
 		case 5:  /* --inspect */
 			args->inspect = 1;
 			break;
@@ -786,6 +794,31 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 
+	/* private devpts namespace? */
+	if (args.pty) {
+		struct stat ptystat;
+		/* make sure /dev/ptmx is a link else we'll just break */
+		ret = lstat("/dev/ptmx", &ptystat);
+		if (ret) {
+			perror("stat /dev/ptmx");
+			exit(1);
+		}
+		if ((ptystat.st_mode & S_IFMT) != S_IFLNK) {
+			printf("Error: /dev/ptmx must be a link to /dev/pts/ptmx\n");
+			exit(1);
+		}
+		ret = unshare(CLONE_NEWNS);
+		if (ret) {
+			perror("unshare mounts ns (for -pty)");
+			exit(1);
+		}
+		ret = mount("pts", "/dev/pts", "devpts", 0, "newinstance");
+		if (ret) {
+			perror("mount -t devpts -o newinstance");
+			exit(1);
+		}
+	}
+
 	/* self-restart ends here: */
 	if (args.self) {
 		restart(getpid(), STDIN_FILENO, RESTART_TASKSELF, args.logfd);
-- 
1.6.1.1