From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories. Date: Wed, 27 May 2009 12:16:09 -0400 (EDT) Message-ID: References: <1243440094.6067.10.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Hannes Reinecke , Kay Sievers , SCSI development list , "Eric W. Biederman" , Andrew Morton , Greg Kroah-Hartman , Kernel development list , Tejun Heo , Cornelia Huck , , "Eric W. Biederman" To: James Bottomley Return-path: Received: from iolanthe.rowland.org ([192.131.102.54]:52077 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751818AbZE0QQH (ORCPT ); Wed, 27 May 2009 12:16:07 -0400 In-Reply-To: <1243440094.6067.10.camel@localhost.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 27 May 2009, James Bottomley wrote: > Hardly ... our current refcounting is on destruction (releases). This > problem is an instance of visibility (the del calls) we need the > visibility teardown to work nicely. We currently have no refcounting on > the visibility. Even if we did (and we could add a ref on when the > underlying device del calls are done), what happens if the target needs > to become visible again. Apparently the generic device infrastructure > can't accept doing an add on a previously del'd device. Definitely not. > The most obvious way of fixing this is to have a special case for > targets of dying hosts ... they could call del early on the > understanding that they're never getting new underlying devices. That > would allow the wait to trigger on the last target del, which is what is > optimal. I don't understand all the subtle issues here. In other contexts, the solution would be to initialize a refcount to 1 when the target is allocated, increment it when a device is added, and decrement it when a device is removed or the host is removed. When the refcount goes to 0, the target is deleted. Why wouldn't this kind of approach work? Alan Stern