[RFC][v5][PATCH 4/8]: Add target_pid parameter to alloc_pidmap()

Sukadev Bhattiprolu
2009-09-07T21:10:41Z

Subject: [RFC][v5][PATCH 4/8]: 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[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>

Index: linux-mmotm/kernel/pid.c
===================================================================
--- linux-mmotm.orig/kernel/pid.c 2009-09-05 21:17:36.000000000 -0700
+++ linux-mmotm/kernel/pid.c 2009-09-05 21:19:11.000000000 -0700
@@ -146,16 +146,22 @@
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;
@@ -168,9 +174,14 @@
do {
if (!test_and_set_bit(offset, map->page)) {
atomic_dec(&map->nr_free);
- pid_ns->last_pid = pid;
+ if (!target_pid)
+ pid_ns->last_pid = pid;
return pid;
+ } else if (target_pid) {
+ rc = -EBUSY;
+ break;
}
+
offset = find_next_offset(map, offset);
pid = mk_pid(pid_ns, map, offset);
/*
@@ -196,6 +207,7 @@
}
pid = mk_pid(pid_ns, map, offset);
}
+
return rc;
}

@@ -272,7 +284,7 @@

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