Introduce struct upid

From: Sukadev Bhattiprolu <[email protected]>

Since task will be visible from different pid namespaces each of them have to be addressed by multiple pids. struct upid is to store the information about which id refers to which namespace.

The constuciton looks like this. Each struct pid carried the reference counter and the list of tasks attached to this pid. At its end it has a variable length array of struct upid-s. Each struct upid has a numerical id (pid itself), pointer to the namespace, this ID is valid in and is hashed into a pid_hash for searching the pids.

The nr and pid_chain fields are kept in struct pid for a while to make kernel still work (no patch initialize the upids yet), but it will be removed at the end of this series when we switch to upids completely.

---

 init_task.h |    6 ++++++
 pid.h       |   16 ++++++++++++++++
 2 files changed, 22 insertions(+)

diff -upr linux-2.6.23-rc1-mm1.orig/include/linux/init_task.h linux-2.6.23-rc1-mm1-7/include/linux/init_task.h
@@ -93,6 +93,12 @@ extern struct group_info init_groups;
 		{ .first = &init_task.pids[PIDTYPE_SID].node },		\
 	},								\
 	.rcu		= RCU_HEAD_INIT,				\
+	.level		= 0,						\
+	.numbers	= { {						\
+		.nr		= 0,					\
+		.ns		= &init_pid_ns,				\
+		.pid_chain	= { .next = NULL, .pprev = NULL },	\
+	}, }								\
 }
 
 #define INIT_PID_LINK(type) 					\

diff -upr linux-2.6.23-rc1-mm1.orig/include/linux/pid.h linux-2.6.23-rc1-mm1-7/include/linux/pid.h
@@ -40,6 +40,20 @@ enum pid_type
  * processes.
  */
 
+
+/*
+ * struct upid is used to get the id of the struct pid, as it is
+ * seen in particular namespace. Later the struct pid is found with
+ * find_pid_ns() using the int nr and struct pid_namespace *ns.
+ */
+
+struct upid {
+	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
+	int nr;
+	struct pid_namespace *ns;
+	struct hlist_node pid_chain;
+};
+
 struct pid
 {
 	atomic_t count;

@@ -50,6 +50,8 @@ struct pid
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
 	struct rcu_head rcu;
+	int level;
+	struct upid numbers[1];
 };
 
 extern struct pid init_struct_pid;

Andrew Morton [[email protected]] wrote:

| On Fri, 10 Aug 2007 15:47:59 +0400
| [email protected] wrote:
| 
| >  struct pid
| >  {
| >  	atomic_t count;
| > @@ -50,6 +50,8 @@ struct pid
| >  	/* lists of tasks that use this pid */
| >  	struct hlist_head tasks[PIDTYPE_MAX];
| >  	struct rcu_head rcu;
| > +	int level;
| > +	struct upid numbers[1];
| 
| You can make this have size [0] now.  It's a gcc extension and
| is used elsewhere in the kernel.

Sorry, we did not respond to this yet :-)

Well, every process has at least one 'struct upid'. The only "cost" I see with size [1] is having to subtract 1 in create_pid_cachep().

Besides, we create/initialize the 'struct pid' for the idle process by hand (see INIT_STRUCT_PID in init_task.h).

If we set this size to [0] now, we would need to dynamically allocate a 'struct upid' during early boot and attach this upid to init_struct_pid.

Or is there a easy way to attach a 'upid' to init_struct_pid, statically ?

Suka