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

[Nadia.Derbey-6ktuUTfB/bM@public.gmane.org]

[-- Attachment #1: upidnr_use_next_id.patch --]
[-- Type: text/plain, Size: 4415 bytes --]

[PATCH 04/04]

This patch makes use of the target ids specified by a previous write to
/proc/self/next_pids 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-6ktuUTfB/bM@public.gmane.org>

---
 kernel/fork.c |    5 ++-
 kernel/pid.c  |   80 ++++++++++++++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 73 insertions(+), 12 deletions(-)

Index: linux-2.6.25-rc3-mm1/kernel/pid.c
===================================================================
--- linux-2.6.25-rc3-mm1.orig/kernel/pid.c	2008-03-10 09:19:02.000000000 +0100
+++ linux-2.6.25-rc3-mm1/kernel/pid.c	2008-03-10 13:45:52.000000000 +0100
@@ -122,14 +122,26 @@ static void free_pidmap(struct upid *upi
 	atomic_inc(&map->nr_free);
 }
 
-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int alloc_pidmap(struct pid_namespace *pid_ns, struct pid_list *pid_l,
+			int level)
 {
 	int i, offset, max_scan, pid, last = pid_ns->last_pid;
 	struct pidmap *map;
 
-	pid = last + 1;
-	if (pid >= pid_max)
-		pid = RESERVED_PIDS;
+	if (!pid_l) {
+		pid = last + 1;
+		if (pid >= pid_max)
+			pid = RESERVED_PIDS;
+	} else {
+		/*
+		 * There's a target pid, so use it instead
+		 */
+		BUG_ON(level < 0);
+		pid = PID_AT(pid_l, level);
+		if (pid >= pid_max)
+			return -EINVAL;
+	}
+
 	offset = pid & BITS_PER_PAGE_MASK;
 	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
 	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
@@ -153,9 +165,16 @@ static int alloc_pidmap(struct pid_names
 			do {
 				if (!test_and_set_bit(offset, map->page)) {
 					atomic_dec(&map->nr_free);
-					pid_ns->last_pid = pid;
+					if (!pid_l)
+						pid_ns->last_pid = pid;
+					else
+						pid_ns->last_pid = max(last,
+									pid);
 					return pid;
 				}
+				if (pid_l)
+					/* Target pid is already in use */
+					return -EBUSY;
 				offset = find_next_offset(map, offset);
 				pid = mk_pid(pid_ns, map, offset);
 			/*
@@ -179,7 +198,7 @@ static int alloc_pidmap(struct pid_names
 		}
 		pid = mk_pid(pid_ns, map, offset);
 	}
-	return -1;
+	return -ENOMEM;
 }
 
 int next_pidmap(struct pid_namespace *pid_ns, int last)
@@ -250,14 +269,55 @@ struct pid *alloc_pid(struct pid_namespa
 	int i, nr;
 	struct pid_namespace *tmp;
 	struct upid *upid;
+	struct pid_list *pid_l = NULL;
+	int rel_level = -1;
+
+	/*
+	 * If there is a list of upid nrs specified, use it instead of letting
+	 * the kernel chose them for us.
+	 */
+	if (current->next_id && (current->next_id->flag & SYS_ID_PID)) {
+		pid_l = current->next_id->pid_ids;
+		BUG_ON(!pid_l);
+		rel_level = pid_l->npids - 1;
+		if (rel_level > ns->level) {
+			pid = ERR_PTR(-EINVAL);
+			goto out;
+		}
+	}
 
 	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
-	if (!pid)
+	if (!pid) {
+		pid = ERR_PTR(-ENOMEM);
 		goto out;
+	}
 
 	tmp = ns;
-	for (i = ns->level; i >= 0; i--) {
-		nr = alloc_pidmap(tmp);
+	/*
+	 * 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_pidmap(tmp, pid_l, rel_level);
+		if (nr < 0)
+			goto out_free;
+
+		pid->numbers[i].nr = nr;
+		pid->numbers[i].ns = tmp;
+		tmp = tmp->parent;
+	}
+
+	if (pid_l) {
+		current->next_id->flag &= ~SYS_ID_PID;
+		pids_free(pid_l);
+		current->next_id->pid_ids = NULL;
+	}
+
+	/*
+	 * Let the lower levels upid nrs be automatically allocated
+	 */
+	for ( ; i >= 0; i--) {
+		nr = alloc_pidmap(tmp, NULL, -1);
 		if (nr < 0)
 			goto out_free;
 
@@ -288,7 +348,7 @@ out_free:
 		free_pidmap(pid->numbers + i);
 
 	kmem_cache_free(ns->pid_cachep, pid);
-	pid = NULL;
+	pid = ERR_PTR(nr);
 	goto out;
 }
 
Index: linux-2.6.25-rc3-mm1/kernel/fork.c
===================================================================
--- linux-2.6.25-rc3-mm1.orig/kernel/fork.c	2008-03-10 09:19:01.000000000 +0100
+++ linux-2.6.25-rc3-mm1/kernel/fork.c	2008-03-10 13:48:03.000000000 +0100
@@ -1197,10 +1197,11 @@ 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));
-		if (!pid)
+		if (IS_ERR(pid)) {
+			retval = PTR_ERR(pid);
 			goto bad_fork_cleanup_io;
+		}
 
 		if (clone_flags & CLONE_NEWPID) {
 			retval = pid_ns_prepare_proc(task_active_pid_ns(p));

--