From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752497Ab2G0TIY (ORCPT ); Fri, 27 Jul 2012 15:08:24 -0400 Received: from mga01.intel.com ([192.55.52.88]:17920 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751965Ab2G0TIX (ORCPT ); Fri, 27 Jul 2012 15:08:23 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="199064633" Date: Fri, 27 Jul 2012 15:08:21 -0400 From: Matthew Wilcox To: Greg KH Cc: Keith Busch , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, Alan Cox Subject: Re: [PATCH] NVMe: Add a character device for each nvme device Message-ID: <20120727190821.GO22985@linux.intel.com> References: <1343407458-29909-1-git-send-email-keith.busch@intel.com> <20120727181212.GM22985@linux.intel.com> <20120727182546.GA23874@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120727182546.GA23874@kroah.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 27, 2012 at 11:25:46AM -0700, Greg KH wrote: > On Fri, Jul 27, 2012 at 02:12:12PM -0400, Matthew Wilcox wrote: > > I don't see a problem here, but I'm no expert at sysfs / character devices. > > Alan, Greg, anyone else see any problems with how this character device is > > created / destroyed? > > Yes, see below: Thanks! > > > + device_create(nvme_char_cl, NULL, MKDEV(nvme_char_major, dev->instance), > > > + NULL, "nvme%d", dev->instance); > > You just created a device at the "root" of sysfs, which is wrong, > especially when you do have a parent device here. Please use it. OK, that makes sense; this device should be the child of the pci_dev that it belongs to. > Also, why are you creating your own class? Can't this just be a misc > device? And if you want to create your own class, please don't, use a > bus, as that is what is really happening here, right? We are trying to > move away from using 'struct class' wherever possible (one of these days > we'll just remove it...) What we're trying to achieve here is to create one character device per NVMe controller that gets plugged in. Each NVMe controller is-a PCI function. The reason we're trying to do this is so that we can send commands to the NVMe controller, even when there is no storage present (eg a drive is shipped from the factory with no configured storage). So we have no particular desire to create a new struct class, or struct bus. If we can create a misc device per PCIe function that's bound to our driver, that's great! Can you recommend a driver that does this already?