[v11][PATCH 3/9] Define set_pidmap() function

Sukadev Bhattiprolu
2009-11-05T05:37:29Z

Subject: [v11][PATCH 3/9] Define set_pidmap() function

Define a set_pidmap() interface which is like alloc_pidmap() only that
caller specifies the pid number to be assigned.

Changelog[v9]:
- Completely rewrote this patch based on Eric Biederman's code.
Changelog[v7]:
- [Eric Biederman] Generalize alloc_pidmap() to take a range of pids.
Changelog[v6]:
- Separate target_pid > 0 case to minimize the number of checks needed.
Changelog[v3]:
- (Eric Biederman): Avoid set_pidmap() function. Added couple of
checks for target_pid in alloc_pidmap() itself.
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@us.ibm.com>
Acked-by: Oren Laadan <orenl@cs.columbia.edu>
---
kernel/pid.c | 41 +++++++++++++++++++++++++++++++++--------
1 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index c4d9914..c849327 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -147,18 +147,19 @@ static int alloc_pidmap_page(struct pidmap *map)
return 0;
}

-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int do_alloc_pidmap(struct pid_namespace *pid_ns, int last, int min,
+ int max)
{
- int i, offset, max_scan, pid, last = pid_ns->last_pid;
+ int i, offset, max_scan, pid;
int rc = -EAGAIN;
struct pidmap *map;

pid = last + 1;
if (pid >= pid_max)
- pid = RESERVED_PIDS;
+ pid = min;
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;
+ max_scan = (max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
for (i = 0; i <= max_scan; ++i) {
rc = alloc_pidmap_page(map);
if (rc)
@@ -168,7 +169,6 @@ 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;
return pid;
}
offset = find_next_offset(map, offset);
@@ -179,16 +179,16 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
* bitmap block and the final block was the same
* as the starting point, pid is before last_pid.
*/
- } while (offset < BITS_PER_PAGE && pid < pid_max &&
+ } while (offset < BITS_PER_PAGE && pid < max &&
(i != max_scan || pid < last ||
!((last+1) & BITS_PER_PAGE_MASK)));
}
- if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
+ if (map < &pid_ns->pidmap[(max-1)/BITS_PER_PAGE]) {
++map;
offset = 0;
} else {
map = &pid_ns->pidmap[0];
- offset = RESERVED_PIDS;
+ offset = min;
if (unlikely(last == offset)) {
rc = -EAGAIN;
break;
@@ -199,6 +199,31 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
return rc;
}

+static int alloc_pidmap(struct pid_namespace *pid_ns)
+{
+ int nr;
+
+ nr = do_alloc_pidmap(pid_ns, pid_ns->last_pid, RESERVED_PIDS, pid_max);
+ if (nr >= 0)
+ pid_ns->last_pid = nr;
+ return nr;
+}
+
+static int set_pidmap(struct pid_namespace *pid_ns, int target)
+{
+ if (!target)
+ return alloc_pidmap(pid_ns);
+
+ if (target >= pid_max)
+ return -EINVAL;
+
+ if ((target < 0) || (target < RESERVED_PIDS &&
+ pid_ns->last_pid >= RESERVED_PIDS))
+ return -EINVAL;
+
+ return do_alloc_pidmap(pid_ns, target - 1, target, target + 1);
+}
+
int next_pidmap(struct pid_namespace *pid_ns, int last)
{
int offset;
--
1.6.0.4