[PATCH 2/2] sys_restore: set the pid number

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Set the pid number for a restored task.  This is purely a toy, as it
only sets the pidnr in the lowest level pid namespace.

Signed-off-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 kernel/fork.c |    5 +++++
 kernel/pid.c  |   19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 0e43f69..41c46d2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1685,6 +1685,8 @@ int unshare_files(struct files_struct **displaced)
 char buf[CKPT_SIZE];
 char exe_filename[PAGE_SIZE];
 
+extern int choose_pidmap(struct pid *pid, int new);
+
 /*
  * userspace will already have made us a new pidns
  */
@@ -1717,6 +1719,9 @@ long do_restore(unsigned int fd,
 	if (nr_scanned != 2)
 		return -EINVAL;
 
+	ret = choose_pidmap(task_pid(current), pid);
+	if (!ret)
+		return -EAGAIN;
 
 	ret = do_execve(exe_filename, argv, envp, regs);
 out:
diff --git a/kernel/pid.c b/kernel/pid.c
index 30bd5d4..88a5e2a 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -122,6 +122,25 @@ static void free_pidmap(struct upid *upid)
 	atomic_inc(&map->nr_free);
 }
 
+int choose_pidmap(struct pid *pid, int new)
+{
+	struct pidmap *map;
+	int level = pid->level;
+	struct upid *upid = &pid->numbers[level];
+	struct pid_namespace *pid_ns = upid->ns;
+	int old = upid->nr;
+
+	map = &pid_ns->pidmap[new/BITS_PER_PAGE];
+	if (!test_and_set_bit(new, map->page)) {
+		map = &pid_ns->pidmap[old/BITS_PER_PAGE];
+		clear_bit(old, map->page);
+		upid->nr = new;
+		return 1;
+	}
+
+	return 0;
+}
+
 static int alloc_pidmap(struct pid_namespace *pid_ns)
 {
 	int i, offset, max_scan, pid, last = pid_ns->last_pid;
-- 
1.5.4.3