Re: [PATCH 1/5] cgroup: ID notification call back

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 24 Aug 2010 17:46:03 -0700
Paul Menage <menage@google.com> wrote:

> On Tue, Aug 24, 2010 at 5:37 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >
> > Ou...I'm sorry but I would like to use attach_id() for this time.
> > Forgive me, above seems a big change.
> > I'd like to write a series of patch to do above, later.
> > At least, to do a trial.
> >
> 
> Sure, for testing outside the tree. I don't think introducing new code
> into mainline that's intentionally ugly and cutting corners is a good
> idea.
> 

Hmm. How this pseudo code looks like ? This passes "new id" via
cgroup->subsys[array] at creation. (Using union will be better, maybe).

---
 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |   26 +++++++++++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)

Index: mmotm-0811/include/linux/cgroup.h
===================================================================
--- mmotm-0811.orig/include/linux/cgroup.h
+++ mmotm-0811/include/linux/cgroup.h
@@ -508,6 +508,7 @@ struct cgroup_subsys {
 	struct cgroupfs_root *root;
 	struct list_head sibling;
 	/* used when use_id == true */
+	int max_id;
 	struct idr idr;
 	spinlock_t id_lock;
 
Index: mmotm-0811/kernel/cgroup.c
===================================================================
--- mmotm-0811.orig/kernel/cgroup.c
+++ mmotm-0811/kernel/cgroup.c
@@ -3335,19 +3335,31 @@ static long cgroup_create(struct cgroup 
 		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 
 	for_each_subsys(root, ss) {
-		struct cgroup_subsys_state *css = ss->create(ss, cgrp);
+		struct cgroup_subsys_state *css;
 
-		if (IS_ERR(css)) {
-			err = PTR_ERR(css);
-			goto err_destroy;
-		}
-		init_cgroup_css(css, ss, cgrp);
 		if (ss->use_id) {
 			err = alloc_css_id(ss, parent, cgrp);
 			if (err)
 				goto err_destroy;
+			/*
+ 			 * Here, created css_id is recorded into
+ 			 * cgrp->subsys[ss->subsys_id]
+			 * array and passed to subsystem.
+			 */
+		} else
+			cgrp->subsys[ss->subsys_id] = NULL;
+
+		css = ss->create(ss, cgrp);
+
+		if (IS_ERR(css)) {
+			/* forget preallocated id */
+			if (cgrp->subsys[ss->subsys_id])
+				free_css_id_direct((struct css_id *)
+					cgrp->subsys[ss->subsys_id]);
+			err = PTR_ERR(css);
+			goto err_destroy;
 		}
-		/* At error, ->destroy() callback has to free assigned ID. */
+		init_cgroup_css(css, ss, cgrp);
 	}
 
 	cgroup_lock_hierarchy(root);