kobject: introduce kobj_completion

A common way to handle kobject lifetimes in embedded in objects with
different lifetime rules is to pair the kobject with a struct completion.

This introduces a kobj_completion structure that can be used in place
of the pairing, along with several convenience functions for
initialization, release, and put-and-wait.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/kobj_completion.h b/include/linux/kobj_completion.h
new file mode 100644 (file)
index 0000000..a428f64
--- /dev/null
+++ b/include/linux/kobj_completion.h
@@ -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_ */

diff --git a/lib/kobject.c b/lib/kobject.c
index e769ee3..a5a9b13 100644 (file)
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -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>
@@ -749,6 +750,55 @@ const struct sysfs_ops kobj_sysfs_ops = {
        .store  = kobj_attr_store,
 };
 
+/**
+ * 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 other outstanding references are also dropped.  This routine
+ * is only necessary once other references may have been taken on the
+ * kobject.  Typically this happens when the kobject has been published
+ * to sysfs via kobject_add.
+ */
+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.