Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264897AbTFLQYC (ORCPT ); Thu, 12 Jun 2003 12:24:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264898AbTFLQYB (ORCPT ); Thu, 12 Jun 2003 12:24:01 -0400 Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:24547 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id S264897AbTFLQXj (ORCPT ); Thu, 12 Jun 2003 12:23:39 -0400 Date: Thu, 12 Jun 2003 17:37:24 +0100 From: viro@parcelfarce.linux.theplanet.co.uk To: Andrey Borzenkov Cc: linux-kernel@vger.kernel.org Subject: Re: True number of device openers in 2.5 Message-ID: <20030612163724.GL6754@parcelfarce.linux.theplanet.co.uk> References: <200306121937.53198.arvidjaar@mail.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200306121937.53198.arvidjaar@mail.ru> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1494 Lines: 30 On Thu, Jun 12, 2003 at 07:37:53PM +0400, Andrey Borzenkov wrote: > For single-partition devices it is just bd_openers but I am more intersted in > multi-partition case. Here I need to know about sum of opens for all > partitions including the whole device. It appears that for a container > bd_openers is incremented for every open of itself and for the _first_ open > of partition and bd_part_count is incremented for every (including first) > open of partition. So bdev->bd_contains->bd_openers + > bdev->bd_contains->bd_part_count really gives an access (number of opened > partitions but this is unknown otherwise). There is no way to get anything useful out of that. _Any_ kernel code that relies on such counters to tell if there's somebody else who might've accessed the thing does not account for the fact that fork() and dup() do not go beyond the struct file. IOW, any place that does if (number of openers == 1) do something that breaks if IO is going on is FUBAR. Variant with if (number of openers == 0) block ->open() do something ... will work, but it means that we are not triggering it from ioctl() on that device. And here we only care about zero/non-zero, so ->bd_openers on the entire disk will do just fine. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/