zdtm: add a small program to create a zdtm container (v2)

I didn't find a way how to do that with help "unshare".
It's simpler to write this program. It looks better than tricks in
zdtm.sh.

v2: proxify exit status
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Ruslan Kuprieiev <kupruser@gmail.com>
Acked-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/.gitignore

@@ -4,3 +4,4 @@
 /dev
 /dump
 /*.log
+/zdtm_ct

test/Makefile

@@ -28,7 +28,13 @@ fault-injection: .FORCE
 zdtm_ns: $(shell echo "$(TST)" | tr ' ' '\n' | grep -P $(EXP))
 zdtm_nons: $(shell echo "$(TST)" | tr ' ' '\n' | grep -vP $(EXP))
 
-$(TST):
+zdtm_ct: zdtm_ct.c
+
+clean:
+	rm -rf zdtm_ct
+	$(MAKE) -C zdtm $@
+
+$(TST): zdtm_ct
 	./zdtm.sh --ct ${ZDTM_ARGS} $(@) &> $(subst /,_,$@).log || \
 	{ flock Makefile cat $(subst /,_,$@).log; exit 1; }
 .PHONY: zdtm_ns

test/zdtm.sh

@@ -881,18 +881,11 @@ while :; do
 		[ -z "$ZDTM_SH_IN_CT" ] && {
 			export ZDTM_SH_IN_CT=1
 			shift
-			args="$@"
 			# pidns is used to avoid conflicts
 			# mntns is used to mount /proc
 			# net is used to avoid conflicts of parasite sockets
-			unshare --pid --mount --ipc --net -- bash -c "
-				(
-					ip link set up dev lo &&
-					mount --make-rprivate / &&
-					umount -l /proc &&
-					mount -t proc proc /proc/ &&
-					./zdtm.sh $args
-				)"
+			make zdtm_ct &&
+			./zdtm_ct ./zdtm.sh "$@"
 			exit
 		}
 		shift

test/zdtm_ct.c

+#define _GNU_SOURCE
+#include <sched.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/mount.h>
+
+int main(int argc, char **argv)
+{
+	pid_t pid;
+	int status;
+
+	/*
+	 *pidns is used to avoid conflicts
+	 * mntns is used to mount /proc
+	 * net is used to avoid conflicts of parasite sockets
+	*/
+	if (unshare(CLONE_NEWNS | CLONE_NEWPID | CLONE_NEWNET | CLONE_NEWIPC))
+		return 1;
+	pid = fork();
+	if (pid == 0) {
+		if (mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL)) {
+			fprintf(stderr, "mount(/, S_REC | MS_PRIVATE)): %m");
+			return 1;
+		}
+		umount2("/proc", MNT_DETACH);
+		umount2("/dev/pts", MNT_DETACH);
+		if (mount("zdtm_proc", "/proc", "proc", 0, NULL)) {
+			fprintf(stderr, "mount(/proc): %m");
+			return 1;
+		}
+		if (mount("zdtm_devpts", "/dev/pts", "devpts", 0,
+					"newinstance,ptmxmode=0666")) {
+			fprintf(stderr, "mount(pts): %m");
+			return 1;
+		}
+		if (mount("/dev/pts/ptmx", "/dev/ptmx", NULL, MS_BIND, NULL)) {
+			fprintf(stderr, "mount(ptmx): %m");
+			return 1;
+		}
+		if (system("ip link set up dev lo"))
+			return 1;
+		execv(argv[1], argv + 1);
+		fprintf(stderr, "execve: %m");
+		return 1;
+	}
+
+	if (waitpid(pid, &status, 0) != pid) {
+		fprintf(stderr, "waitpid: %m");
+		return 1;
+	}
+
+	if (WIFEXITED(status))
+		return WEXITSTATUS(status);
+	else if (WIFSIGNALED(status))
+		kill(getpid(), WTERMSIG(status));
+	else
+		fprintf(stderr, "Unexpected exit status: %x\n", status);
+
+	return 1;
+}