Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZ do?

+#define DEBUG
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/unistd.h>

@@ -959,10 +959,19 @@ static struct task_struct *copy_process(unsigned long cl
 	int retval;
 	struct task_struct *p;
 	int cgroup_callbacks_done = 0;
+	pid_t clone_pid = stack_size;

 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
 		return ERR_PTR(-EINVAL);

+	/* We only allow the clone_with_pid when a new pid namespace is
+	 * created. FIXME: how to restrict it.
+	 */
+	if ((clone_flags & CLONE_NEWPID) && (clone_flags & CLONE_WITH_PID))
+		return ERR_PTR(-EINVAL);
+	if ((clone_flags & CLONE_WITH_PID) && (clone_pid <= 1))
+		return ERR_PTR(-EINVAL);

 	/*
 	 * Thread groups must share signals as well, and detached threads
 	 * can only be started up within the thread group.

@@ -1135,7 +1144,10 @@ static struct task_struct *copy_process(unsigned long c

 	if (pid != &init_struct_pid) {
 		retval = -ENOMEM;
-		pid = alloc_pid(task_active_pid_ns(p));
+		if (clone_flags & CLONE_WITH_PID)
+			pid = alloc_pid(task_active_pid_ns(p), clone_pid);
+		else
+			pid = alloc_pid(task_active_pid_ns(p), 0);

-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int alloc_pidmap(struct pid_namespace *pid_ns, pid_t pid_nr)
 {
 	int i, offset, max_scan, pid, last = pid_ns->last_pid;
 	struct pidmap *map;

-	pid = last + 1;
+	if (pid_nr)
+		pid = pid_nr;
+	else
+		pid = last + 1;

 	if (pid >= pid_max)
 		pid = RESERVED_PIDS;
 	offset = pid & BITS_PER_PAGE_MASK;

@@ -153,9 +156,12 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
 			do {
 				if (!test_and_set_bit(offset, map->page)) {
 					atomic_dec(&map->nr_free);
-					pid_ns->last_pid = pid;
+					if (!pid_nr)
+						pid_ns->last_pid = pid;
 					return pid;
 				}
+				if (pid_nr)
+					return -1;
 				offset = find_next_offset(map, offset);
 				pid = mk_pid(pid_ns, map, offset);
 			/*

@@ -239,21 +245,25 @@ void free_pid(struct pid *pid)
 	call_rcu(&pid->rcu, delayed_put_pid);
 }

-struct pid *alloc_pid(struct pid_namespace *ns)
+struct pid *alloc_pid(struct pid_namespace *ns, pid_t pid_nr)
 {
 	struct pid *pid;
 	enum pid_type type;
 	int i, nr;
 	struct pid_namespace *tmp;
 	struct upid *upid;
+	int level = ns->level;
+
+	if (pid_nr >= pid_max)
+		return NULL;

 	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
 	if (!pid)
 		goto out;

-	tmp = ns;
-	for (i = ns->level; i >= 0; i--) {
-		nr = alloc_pidmap(tmp);
+	tmp = ns->parent;
+	for (i = level-1; i >= 0; i--) {
+		nr = alloc_pidmap(tmp, 0);
 		if (nr < 0)
 			goto out_free;

@@ -262,6 +272,14 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 		tmp = tmp->parent;
 	}

+	nr = alloc_pidmap(ns, pid_nr);
+	if (nr < 0)
+		goto out_free;
+	pid->numbers[level].nr = nr;
+	pid->numbers[level].ns = ns;
+	if (nr == pid_nr)
+		pr_debug("nr == pid_nr == %d\n", nr);
+
 	get_pid_ns(ns);
 	pid->level = ns->level;
 	atomic_set(&pid->count, 1);

On Thu, Mar 12, 2009 at 2:21 PM, Serge E. Hallyn [off-list ref] wrote:

quoted

Quoting Greg Kurz (gkurz-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org):

quoted

On Thu, 2009-03-12 at 09:53 -0500, Serge E. Hallyn wrote:

quoted

Or are you suggesting that you'll do a dummy clone of (5594,2) so that
the next clone(CLONE_NEWPID) will be expected to be (5594,3,1)?

Of course not

Ok - someone *did* argue that at some point I think...

quoted

but one should be able to tell clone() to pick a specific
pid.

Can you explain exactly how?  I must be missing something clever.

-serge

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