From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932733Ab2JVA51 (ORCPT ); Sun, 21 Oct 2012 20:57:27 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:51318 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754692Ab2JVA5Z (ORCPT ); Sun, 21 Oct 2012 20:57:25 -0400 From: Dmitry Torokhov To: Al Viro , Dave Jones Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-input@vger.kernel.org Subject: [PATCH 1/2] char_dev: pin parent kobject Date: Sun, 21 Oct 2012 17:57:19 -0700 Message-Id: <1350867440-6109-1-git-send-email-dmitry.torokhov@gmail.com> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <20121021073928.GV2616@ZenIV.linux.org.uk> References: <20121021073928.GV2616@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In certain cases (for example when a cdev structure is embedded into another object whose lifetime is controlled by a separate kobject) it is beneficial to tie lifetime of another object to the lifetime of character device so that related object is not freed until after char_dev object is freed. To achieve this let's pin kobject's parent when doing cdev_add() and unpin when last reference to cdev structure is being released. Signed-off-by: Dmitry Torokhov --- OK, so it looks like cdev kobject's parent is unused so we can just have users set themselves as parents of character device and have cdev_add() pin it. fs/char_dev.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/fs/char_dev.c b/fs/char_dev.c index 3f152b9..afc2bb6 100644 --- a/fs/char_dev.c +++ b/fs/char_dev.c @@ -471,9 +471,19 @@ static int exact_lock(dev_t dev, void *data) */ int cdev_add(struct cdev *p, dev_t dev, unsigned count) { + int error; + p->dev = dev; p->count = count; - return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p); + + error = kobj_map(cdev_map, dev, count, NULL, + exact_match, exact_lock, p); + if (error) + return error; + + kobject_get(p->kobj.parent); + + return 0; } static void cdev_unmap(dev_t dev, unsigned count) @@ -498,14 +508,20 @@ void cdev_del(struct cdev *p) static void cdev_default_release(struct kobject *kobj) { struct cdev *p = container_of(kobj, struct cdev, kobj); + struct kobject *parent = kobj->parent; + cdev_purge(p); + kobject_put(parent); } static void cdev_dynamic_release(struct kobject *kobj) { struct cdev *p = container_of(kobj, struct cdev, kobj); + struct kobject *parent = kobj->parent; + cdev_purge(p); kfree(p); + kobject_put(parent); } static struct kobj_type ktype_cdev_default = { -- 1.7.11.7