[RFC][v7][PATCH 4/9]: Add target_pid parameter to alloc_pidmap()

Sukadev Bhattiprolu
2009-09-24T17:02:55Z

Subject: [RFC][v7][PATCH 4/9]: Add target_pid parameter to alloc_pidmap()

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

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@linux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
---
kernel/pid.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

Index: linux-2.6/kernel/pid.c
===================================================================
--- linux-2.6.orig/kernel/pid.c 2009-09-09 19:07:20.000000000 -0700
+++ linux-2.6/kernel/pid.c 2009-09-10 10:23:27.000000000 -0700
@@ -146,16 +146,22 @@ static int alloc_pidmap_page(struct pidm
return 0;
}

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

- pid = last + 1;
- if (pid >= pid_max)
- pid = RESERVED_PIDS;
+ if (target_pid) {
+ pid = target_pid;
+ if (pid < 0 || pid >= pid_max)
+ return -EINVAL;
+ } else {
+ pid = last + 1;
+ if (pid >= pid_max)
+ pid = RESERVED_PIDS;
+ }
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;
@@ -164,6 +170,15 @@ static int alloc_pidmap(struct pid_names
if (rc)
break;

+ if (target_pid) {
+ rc = -EBUSY;
+ if (!test_and_set_bit(offset, map->page)) {
+ atomic_dec(&map->nr_free);
+ rc = pid;
+ }
+ return rc;
+ }
+
if (likely(atomic_read(&map->nr_free))) {
do {
if (!test_and_set_bit(offset, map->page)) {
@@ -196,6 +211,7 @@ static int alloc_pidmap(struct pid_names
}
pid = mk_pid(pid_ns, map, offset);
}
+
return rc;
}

@@ -272,7 +288,7 @@ struct pid *alloc_pid(struct pid_namespa

tmp = ns;
for (i = ns->level; i >= 0; i--) {
- nr = alloc_pidmap(tmp);
+ nr = alloc_pidmap(tmp, 0);
if (nr < 0)
goto out_free;