linux-kernel - [RFC][v6][PATCH 4/9]: Add target_pid parameter to alloc

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Message-ID: <20090910060955.GC25883@us.ibm.com>
Date:	Wed, 9 Sep 2009 23:09:55 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Oren Laadan <orenl@...columbia.edu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
	Nathan Lynch <nathanl@...tin.ibm.com>, arnd@...db.de,
	container@...ibm.com, sukadev@...ibm.com
Subject: [RFC][v6][PATCH 4/9]: Add target_pid parameter to alloc_pidmap()



Subject: [RFC][v6][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[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@...ux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue@...ibm.com>
---
 kernel/pid.c |   24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 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	2009-09-09 19:07:28.000000000 -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;
@@ -168,9 +174,14 @@ static int alloc_pidmap(struct pid_names
 			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 @@ static int alloc_pidmap(struct pid_names
 		}
 		pid = mk_pid(pid_ns, map, offset);
 	}
+
 	return rc;
 }
 
@@ -272,7 +284,7 @@ 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;
 
--
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