[RFC][v4][PATCH 3/7]: Add target_pid parameter to alloc_pidmap()

[Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

Subject: [RFC][v4][PATCH 3/7]: Add target_pid parameter to alloc_pidmap()

With support for setting a specific pid number for a process,
alloc_pidmap() will need a paramter a 'target_pid' parameter.

Changelog[v2]:
	- (Serge Hallyn) Check for 'pid < 0' in set_pidmap().(Code
	  actually checks for 'pid <= 0' for completeness).

Signed-off-by: Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Acked-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Reviewed-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 kernel/pid.c |   28 ++++++++++++++++++++++++++--
 1 files changed, 26 insertions(+), 2 deletions(-)

Index: linux-2.6/kernel/pid.c
===================================================================
--- linux-2.6.orig/kernel/pid.c	2009-08-05 17:02:45.000000000 -0700
+++ linux-2.6/kernel/pid.c	2009-08-05 19:34:37.000000000 -0700
@@ -147,11 +147,35 @@
 	return 0;
 }
 
-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int set_pidmap(struct pid_namespace *pid_ns, int pid)
+{
+	int offset;
+	struct pidmap *map;
+
+	if (pid <= 0 || pid >= pid_max)
+		return -EINVAL;
+
+	offset = pid & BITS_PER_PAGE_MASK;
+	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
+
+	if (alloc_pidmap_page(map))
+		return -ENOMEM;
+
+	if (test_and_set_bit(offset, map->page))
+		return -EBUSY;
+
+	atomic_dec(&map->nr_free);
+	return pid;
+}
+
+static int alloc_pidmap(struct pid_namespace *pid_ns, int target_pid)
 {
 	int i, rc, offset, max_scan, pid, last = pid_ns->last_pid;
 	struct pidmap *map;
 
+	if (target_pid)
+		return set_pidmap(pid_ns, target_pid);
+
 	pid = last + 1;
 	if (pid >= pid_max)
 		pid = RESERVED_PIDS;
@@ -270,7 +294,7 @@
 
 	tmp = ns;
 	for (i = ns->level; i >= 0; i--) {
-		nr = alloc_pidmap(tmp);
+		nr = alloc_pidmap(tmp, 0);
 		if (nr < 0)
 			goto out_free;