[Devel] [RFC][PATCH 04/14] Add struct pid_nr and pid_nrs list

[sukadev at us.ibm.com]

From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
Subject: [RFC][PATCH 04/14] Add struct pid_nr and pid_nrs list

A struct pid_nr associates a pid_t value with a pid namespace. We attach
a list of struct pid_nr entries to a struct pid (pid->pid_nrs), allowing
the struct pid to take different pid_t values in different namespaces.

The pid->pid_nrs list and the helper functions will be used in subsequent
functions.

Changelog:
	- [Serge Hallyn comment]: Remove (!pid_nr) check in free_pid_nr()

Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
---
 include/linux/pid.h |   23 +++++++++++++++++++++++
 kernel/pid.c        |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

Index: lx26-21-rc3-mm2/include/linux/pid.h
===================================================================
--- lx26-21-rc3-mm2.orig/include/linux/pid.h	2007-03-20 15:55:52.000000000 -0700
+++ lx26-21-rc3-mm2/include/linux/pid.h	2007-03-20 17:18:10.000000000 -0700
@@ -11,6 +11,25 @@ enum pid_type
 	PIDTYPE_MAX
 };
 
+struct pid_namespace;
+
+/*
+ * A struct pid_nr holds a process identifier (or pid->nr) for a given
+ * pid namespace.
+ *
+ * A list of struct pid_nr is stored in the struct pid. this list is
+ * used to get the process identifier associated with the pid
+ * namespace it is being seen from.
+ */
+struct pid_nr
+{
+	struct hlist_node node;
+	int nr;
+	struct hlist_node pid_chain;
+	struct pid *pid;
+	struct pid_namespace* pid_ns;
+};
+
 /*
  * What is struct pid?
  *
@@ -49,6 +68,7 @@ struct pid
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
 	struct rcu_head rcu;
+	struct hlist_head pid_nrs;
 };
 
 extern struct pid init_struct_pid;
@@ -95,6 +115,9 @@ extern struct pid *FASTCALL(find_pid(int
 extern struct pid *find_get_pid(int nr);
 extern struct pid *find_ge_pid(int nr);
 
+extern void free_pid_nr(struct pid_nr *pid_nr);
+extern struct pid_nr *alloc_pid_nr(struct pid_namespace *pid_ns,
+			struct pid *pid);
 extern struct pid *alloc_pid(void);
 extern void FASTCALL(free_pid(struct pid *pid));
 
Index: lx26-21-rc3-mm2/kernel/pid.c
===================================================================
--- lx26-21-rc3-mm2.orig/kernel/pid.c	2007-03-20 15:55:52.000000000 -0700
+++ lx26-21-rc3-mm2/kernel/pid.c	2007-03-20 17:53:54.000000000 -0700
@@ -33,6 +33,7 @@
 static struct hlist_head *pid_hash;
 static int pidhash_shift;
 static struct kmem_cache *pid_cachep;
+static struct kmem_cache *pid_nr_cachep;
 struct pid init_struct_pid = INIT_STRUCT_PID;
 
 int pid_max = PID_MAX_DEFAULT;
@@ -190,6 +191,16 @@ static void delayed_put_pid(struct rcu_h
 	put_pid(pid);
 }
 
+void free_pid_nr(struct pid_nr *pid_nr)
+{
+	free_pidmap(pid_nr->pid_ns, pid_nr->nr);
+
+	hlist_del_init(&pid_nr->node);
+
+	put_pid_ns(pid_nr->pid_ns);
+	kmem_cache_free(pid_nr_cachep, pid_nr);
+}
+
 fastcall void free_pid(struct pid *pid)
 {
 	/* We can be called with write_lock_irq(&tasklist_lock) held */
@@ -203,6 +214,40 @@ fastcall void free_pid(struct pid *pid)
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
+struct pid_nr *alloc_pid_nr(struct pid_namespace *pid_ns, struct pid *pid)
+{
+	struct pid_nr* pid_nr;
+	int nr;
+
+	nr = alloc_pidmap(pid_ns);
+	if (nr < 0)
+		return NULL;
+
+	pid_nr = kmem_cache_alloc(pid_nr_cachep, GFP_KERNEL);
+	if (!pid_nr) {
+		free_pidmap(pid_ns, nr);
+		return NULL;
+	}
+
+	INIT_HLIST_NODE(&pid_nr->node);
+	INIT_HLIST_NODE(&pid_nr->pid_chain);
+	pid_nr->pid_ns = pid_ns;
+	get_pid_ns(pid_ns);
+	pid_nr->nr = nr;
+	/*
+	 * The struct pid and list of struct pid_nrs represent a process
+	 * with multiple pid_t values, one in each pid namespace. The list
+	 * of pid_t values of a process, represented by pid->pid_nrs list,
+	 * never changes during the life of the process. As such, struct
+	 * pid and its pid_nrs list maybe viewed as a single object i.e
+	 * they are created/destroyed together.  So we do not need a
+	 * reference to struct pid here.
+	 */
+	pid_nr->pid = pid;
+
+	return pid_nr;
+}
+
 struct pid *alloc_pid(void)
 {
 	struct pid *pid;
@@ -415,4 +460,8 @@ void __init pidmap_init(void)
 	pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
 					__alignof__(struct pid),
 					SLAB_PANIC, NULL, NULL);
+
+	pid_nr_cachep = kmem_cache_create("pid_nr", sizeof(struct pid_nr),
+					  __alignof__(struct pid_nr),
+					  SLAB_PANIC, NULL, NULL);
 }
_______________________________________________
Containers mailing list
Containers at lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers