rst: Create custom proc every time we restore a namespace

We need own proc for restoring mount namespace, since the proc should
be umounted and mounted back diring namespace restore and I don't want
to introduce a special kludge for this.

One more notice -- the temp proc is mounted _after_ namespaces recreation
for the same reason (it will be umounted by prepare_mnt_ns).
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -812,6 +812,40 @@ static void restore_pgid(void)
 
 static char proc_mountpoint[PATH_MAX] = "/proc";
 
+static int prepare_proc(void)
+{
+	snprintf(proc_mountpoint, sizeof(proc_mountpoint), "/tmp/crtools-proc.XXXXXX");
+	if (mkdtemp(proc_mountpoint) == NULL) {
+		pr_err("mkdtemp failed %m");
+		return -1;
+	}
+
+	return 0;
+}
+
+static void umount_proc(void)
+{
+	int err;
+	err = umount(proc_mountpoint);
+	if (err == -1)
+		pr_err("Can't umount %s\n", proc_mountpoint);
+	err = rmdir(proc_mountpoint);
+	if (err == -1)
+		pr_err("Can't delete %s\n", proc_mountpoint);
+}
+
+static void mount_proc(void)
+{
+	int ret;
+
+	ret = mount("proc", proc_mountpoint, "proc", MS_MGC_VAL, NULL);
+	if (ret == -1) {
+		pr_err("mount failed");
+		exit(1);
+	}
+	set_proc_mountpoint(proc_mountpoint);
+}
+
 static bool restore_before_setsid(struct pstree_item *child)
 {
 	int csid = child->born_sid == -1 ? child->sid : child->born_sid;
@@ -840,15 +874,6 @@ static int restore_task_with_children(void *_arg)
 		exit(-1);
 	}
 
-	if (pid == 1) { /* New pid namespace */
-		ret = mount("proc", proc_mountpoint, "proc", MS_MGC_VAL, NULL);
-		if (ret == -1) {
-			pr_err("mount failed");
-			exit(1);
-		}
-		set_proc_mountpoint(proc_mountpoint);
-	}
-
 	ret = log_init_by_pid();
 	if (ret < 0)
 		exit(1);
@@ -857,6 +882,8 @@ static int restore_task_with_children(void *_arg)
 		ret = prepare_namespace(me->pid.virt, ca->clone_flags);
 		if (ret)
 			exit(-1);
+
+		mount_proc();
 	}
 
 	/*
@@ -927,6 +954,15 @@ static int restore_root_task(struct pstree_item *init, struct cr_options *opts)
 		return -1;
 	}
 
+	/*
+	 * We need non /proc proc mount for restoring pid and mount namespaces
+	 * and do not care for the rest of the cases. Thus -- mount proc at
+	 * custom location for any new namespace
+	 */
+
+	if (opts->namespaces_flags && prepare_proc())
+		return -1;
+
 	/*
 	 * FIXME -- currently we assume that all the tasks live
 	 * in the same set of namespaces. This is done to debug
@@ -940,13 +976,6 @@ static int restore_root_task(struct pstree_item *init, struct cr_options *opts)
 			pr_err("crtools should be re-executed with --namespace pid\n");
 			return -1;
 		}
-
-		snprintf(proc_mountpoint, sizeof(proc_mountpoint), "/tmp/crtools-proc.XXXXXX");
-		if (mkdtemp(proc_mountpoint) == NULL) {
-			pr_err("mkdtemp failed %m");
-			return -1;
-		}
-
 	} else	if (opts->namespaces_flags & CLONE_NEWPID) {
 		pr_err("Can't restore pid namespace without the process init\n");
 		return -1;
@@ -971,15 +1000,8 @@ static int restore_root_task(struct pstree_item *init, struct cr_options *opts)
 	ret = (int)futex_get(&task_entries->nr_in_progress);
 
 out:
-	if (init->pid.virt == 1) {
-		int err;
-		err = umount(proc_mountpoint);
-		if (err == -1)
-			pr_err("Can't umount %s\n", proc_mountpoint);
-		err = rmdir(proc_mountpoint);
-		if (err == -1)
-			pr_err("Can't delete %s\n", proc_mountpoint);
-	}
+	if (opts->namespaces_flags)
+		umount_proc();
 
 	if (ret < 0) {
 		struct pstree_item *pi;