[PATCH 4/4] - v2 - PID: use the target ID specified in procfs

[Nadia . Derbey]

[PATCH 04/04]

This patch makes use of the target ids specified by a previous write to
/proc/self/task/<tid>/next_id as the ids to use to allocate the next upid nrs.
Upper levels upid nrs that are not specified in next_pids file are left to the
kernel choice.

Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>

---
 include/linux/pid.h |    2 
 kernel/fork.c       |    3 -
 kernel/pid.c        |  141 +++++++++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 126 insertions(+), 20 deletions(-)

Index: linux-2.6.25-rc8-mm2/include/linux/pid.h
===================================================================
--- linux-2.6.25-rc8-mm2.orig/include/linux/pid.h	2008-04-17 12:50:22.000000000 +0200
+++ linux-2.6.25-rc8-mm2/include/linux/pid.h	2008-04-17 17:42:11.000000000 +0200
@@ -121,7 +121,7 @@ extern struct pid *find_get_pid(int nr);
 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
 int next_pidmap(struct pid_namespace *pid_ns, int last);
 
-extern struct pid *alloc_pid(struct pid_namespace *ns);
+extern struct pid *alloc_pid(struct pid_namespace *ns, int *retval);
 extern void free_pid(struct pid *pid);
 
 /*
Index: linux-2.6.25-rc8-mm2/kernel/fork.c
===================================================================
--- linux-2.6.25-rc8-mm2.orig/kernel/fork.c	2008-04-17 13:49:09.000000000 +0200
+++ linux-2.6.25-rc8-mm2/kernel/fork.c	2008-04-17 17:42:48.000000000 +0200
@@ -1200,8 +1200,7 @@ static struct task_struct *copy_process(
 		goto bad_fork_cleanup_io;
 
 	if (pid != &init_struct_pid) {
-		retval = -ENOMEM;
-		pid = alloc_pid(task_active_pid_ns(p));
+		pid = alloc_pid(task_active_pid_ns(p), &retval);
 		if (!pid)
 			goto bad_fork_cleanup_io;
 
Index: linux-2.6.25-rc8-mm2/kernel/pid.c
===================================================================
--- linux-2.6.25-rc8-mm2.orig/kernel/pid.c	2008-04-17 12:50:25.000000000 +0200
+++ linux-2.6.25-rc8-mm2/kernel/pid.c	2008-04-17 17:50:00.000000000 +0200
@@ -122,6 +122,26 @@ static void free_pidmap(struct upid *upi
 	atomic_inc(&map->nr_free);
 }
 
+static inline int alloc_pidmap_page(struct pidmap *map)
+{
+	if (unlikely(!map->page)) {
+		void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+		/*
+		 * Free the page if someone raced with us
+		 * installing it:
+		 */
+		spin_lock_irq(&pidmap_lock);
+		if (map->page)
+			kfree(page);
+		else
+			map->page = page;
+		spin_unlock_irq(&pidmap_lock);
+		if (unlikely(!map->page))
+			return -1;
+	}
+	return 0;
+}
+
 static int alloc_pidmap(struct pid_namespace *pid_ns)
 {
 	int i, offset, max_scan, pid, last = pid_ns->last_pid;
@@ -134,21 +154,8 @@ static int alloc_pidmap(struct pid_names
 	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
 	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
 	for (i = 0; i <= max_scan; ++i) {
-		if (unlikely(!map->page)) {
-			void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-			/*
-			 * Free the page if someone raced with us
-			 * installing it:
-			 */
-			spin_lock_irq(&pidmap_lock);
-			if (map->page)
-				kfree(page);
-			else
-				map->page = page;
-			spin_unlock_irq(&pidmap_lock);
-			if (unlikely(!map->page))
-				break;
-		}
+		if (unlikely(alloc_pidmap_page(map)))
+			break;
 		if (likely(atomic_read(&map->nr_free))) {
 			do {
 				if (!test_and_set_bit(offset, map->page)) {
@@ -182,6 +189,35 @@ static int alloc_pidmap(struct pid_names
 	return -1;
 }
 
+/*
+ * Return a predefined pid value if successful (ID_AT(pid_l, level)),
+ * -errno else
+ */
+static int alloc_fixed_pidmap(struct pid_namespace *pid_ns,
+			struct sys_id *pid_l, int level)
+{
+	int offset, pid;
+	struct pidmap *map;
+
+	pid = ID_AT(pid_l, level);
+	if (pid < RESERVED_PIDS || pid >= pid_max)
+		return -EINVAL;
+
+	map = &pid_ns->pidmap[pid / BITS_PER_PAGE];
+
+	if (unlikely(alloc_pidmap_page(map)))
+		return -ENOMEM;
+
+	offset = pid & BITS_PER_PAGE_MASK;
+	if (test_and_set_bit(offset, map->page))
+		return -EBUSY;
+
+	atomic_dec(&map->nr_free);
+	pid_ns->last_pid = max(pid_ns->last_pid, pid);
+
+	return pid;
+}
+
 int next_pidmap(struct pid_namespace *pid_ns, int last)
 {
 	int offset;
@@ -243,20 +279,91 @@ void free_pid(struct pid *pid)
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
-struct pid *alloc_pid(struct pid_namespace *ns)
+/*
+ * Called by alloc_pid() to use a list of predefined ids for the calling
+ * process' upper ns levels.
+ * Returns next pid ns to visit if successful (may be NULL if walked through
+ * the entire pid ns hierarchy).
+ * i is filled with next level to be visited (useful for the error cases).
+ */
+static struct pid_namespace *set_predefined_pids(struct pid_namespace *ns,
+						struct pid *pid,
+						struct sys_id *pid_l,
+						int *next_level)
+{
+	struct pid_namespace *tmp;
+	int rel_level, i, nr;
+
+	rel_level = pid_l->nids - 1;
+	if (rel_level > ns->level)
+		return ERR_PTR(-EINVAL);
+
+	tmp = ns;
+
+	/*
+	 * Use the predefined upid nrs for levels ns->level down to
+	 * ns->level - rel_level
+	 */
+	for (i = ns->level ; rel_level >= 0; i--, rel_level--) {
+		nr = alloc_fixed_pidmap(tmp, pid_l, rel_level);
+		if (nr < 0) {
+			tmp = ERR_PTR(nr);
+			goto out;
+		}
+
+		pid->numbers[i].nr = nr;
+		pid->numbers[i].ns = tmp;
+		tmp = tmp->parent;
+	}
+
+	id_blocks_free(pid_l);
+out:
+	*next_level = i;
+	return tmp;
+}
+
+struct pid *alloc_pid(struct pid_namespace *ns, int *retval)
 {
 	struct pid *pid;
 	enum pid_type type;
 	int i, nr;
 	struct pid_namespace *tmp;
 	struct upid *upid;
+	struct sys_id *pid_l;
 
+	*retval = -ENOMEM;
 	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
 	if (!pid)
 		goto out;
 
 	tmp = ns;
-	for (i = ns->level; i >= 0; i--) {
+	i = ns->level;
+
+	/*
+	 * If there is a list of upid nrs specified, use it instead of letting
+	 * the kernel chose the upid nrs for us.
+	 */
+	pid_l = current->next_id;
+	if (pid_l && pid_l->nids) {
+		/*
+		 * returns the next ns to be visited in the following loop
+		 * (or NULL if we are done).
+		 * i is filled in with the next level to be visited. We need
+		 * it to undo things in the error cases.
+		 */
+		tmp = set_predefined_pids(ns, pid, pid_l, &i);
+		if (IS_ERR(tmp)) {
+			*retval = PTR_ERR(tmp);
+			goto out_free;
+		}
+		current->next_id = NULL;
+	}
+
+	*retval = -ENOMEM;
+	/*
+	 * Let the lower levels upid nrs be automatically allocated
+	 */
+	for ( ; i >= 0; i--) {
 		nr = alloc_pidmap(tmp);
 		if (nr < 0)
 			goto out_free;

--
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