[PATCH 1/2] kobject: introduce kobj_completion

[Jeff Mahoney <jeffm@suse.com>]

ext4 exports per-filesystem information via sysfs. The lifetime rules
have historically been painful for this but the solution has been to pair
the kobject with a completion and call complete in the kobject's
release function.

Since this is a pattern I've used in btrfs as well, it makes sense to
turn the pairing into a convenience structure with a standard API.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 include/linux/kobj_completion.h |   18 +++++++++++++++
 lib/kobject.c                   |   47 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ b/include/linux/kobj_completion.h	2013-09-10 12:58:03.530554144 -0400
@@ -0,0 +1,18 @@
+#ifndef _KOBJ_COMPLETION_H_
+#define _KOBJ_COMPLETION_H_
+
+#include <linux/kobject.h>
+#include <linux/completion.h>
+
+struct kobj_completion {
+	struct kobject kc_kobj;
+	struct completion kc_unregister;
+};
+
+#define kobj_to_kobj_completion(kobj) \
+	container_of(kobj, struct kobj_completion, kc_kobj)
+
+void kobj_completion_init(struct kobj_completion *kc, struct kobj_type *ktype);
+void kobj_completion_release(struct kobject *kobj);
+void kobj_completion_del_and_wait(struct kobj_completion *kc);
+#endif /* _KOBJ_COMPLETION_H_ */
--- a/lib/kobject.c	2013-09-10 12:57:54.198666613 -0400
+++ b/lib/kobject.c	2013-09-10 13:16:31.750607946 -0400
@@ -13,6 +13,7 @@
  */
 
 #include <linux/kobject.h>
+#include <linux/kobj_completion.h>
 #include <linux/string.h>
 #include <linux/export.h>
 #include <linux/stat.h>
@@ -711,6 +712,52 @@ const struct sysfs_ops kobj_sysfs_ops =
 };
 
 /**
+ * kobj_completion_init - initialize a kobj_completion object.
+ * @kc: kobj_completion
+ * @ktype: type of kobject to initialize
+ *
+ * kobj_completion structures can be embedded within structures with different
+ * lifetime rules.  During the release of the enclosing object, we can
+ * wait on the release of the kobject so that we don't free it while it's
+ * still busy.
+ */
+void kobj_completion_init(struct kobj_completion *kc, struct kobj_type *ktype)
+{
+	init_completion(&kc->kc_unregister);
+	kobject_init(&kc->kc_kobj, ktype);
+}
+EXPORT_SYMBOL_GPL(kobj_completion_init);
+
+/**
+ * kobj_completion_release - release a kobj_completion object
+ * @kobj: kobject embedded in kobj_completion
+ *
+ * Used with kobject_release to notify waiters that the kobject has been
+ * released.
+ */
+void kobj_completion_release(struct kobject *kobj)
+{
+	struct kobj_completion *kc = kobj_to_kobj_completion(kobj);
+	complete(&kc->kc_unregister);
+}
+EXPORT_SYMBOL_GPL(kobj_completion_release);
+
+/**
+ * kobj_completion_del_and_wait - release the kobject and wait for it
+ * @kc: kobj_completion object to release
+ *
+ * Delete the kobject from sysfs and  drop the reference count. Then wait
+ * until any outstanding references are also dropped.
+ */
+void kobj_completion_del_and_wait(struct kobj_completion *kc)
+{
+	kobject_del(&kc->kc_kobj);
+	kobject_put(&kc->kc_kobj);
+	wait_for_completion(&kc->kc_unregister);
+}
+EXPORT_SYMBOL_GPL(kobj_completion_del_and_wait);
+
+/**
  * kset_register - initialize and add a kset.
  * @k: kset.
  */

-- 
Jeff Mahoney
SUSE Labs