Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757609Ab1DHQnV (ORCPT ); Fri, 8 Apr 2011 12:43:21 -0400 Received: from mail-gx0-f174.google.com ([209.85.161.174]:56476 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752433Ab1DHQnT convert rfc822-to-8bit (ORCPT ); Fri, 8 Apr 2011 12:43:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=HqOFoVySqzcM0TXZ8ULBf8/cMYKHArs1Hmj920uM3mmMDfex7QiP4Cma1plVoJcn2r HZRyOlP8bpCUI2hf/255LrkDlpmW/peMO4MqDT63e4qjZ00CUJ5gZeXE452iV86KZtkf fK7J7Eje1uXhVyHOSbUmqKUJap3fNTH39EKKI= MIME-Version: 1.0 In-Reply-To: <20110408162041.GB3871@mtj.dyndns.org> References: <8d830b21c0b944d26f29dc1e0c42c0bef8d448c2.1301595169.git.amit.shah@redhat.com> <20110401154327.GA6593@mtj.dyndns.org> <20110405065129.GC2872@amit-x200.redhat.com> <20110406100620.GA4142@mtj.dyndns.org> <20110408162041.GB3871@mtj.dyndns.org> Date: Fri, 8 Apr 2011 17:43:16 +0100 Message-ID: Subject: Re: [PATCH] sr: Ensure disk is revalidated when media changes From: Stefan Hajnoczi To: Tejun Heo Cc: Amit Shah , linux-kernel@vger.kernel.org, Jens Axboe , "James E.J. Bottomley" , linux-scsi@vger.kernel.org, Markus Armbruster Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1993 Lines: 43 On Fri, Apr 8, 2011 at 5:20 PM, Tejun Heo wrote: > Hello, > > On Fri, Apr 08, 2011 at 12:37:56PM +0100, Stefan Hajnoczi wrote: >> There is a related issue I have been discussing with Amit: >> https://lkml.org/lkml/2011/3/23/156 >> >> On media change the inode size is not updated by the sr driver or the >> universal cdrom driver. ?A userspace process that holds a /dev/sr0 >> file descriptor open across media change causes all processes on the >> system to see the old medium size when they do lseek(fd, 0, SEEK_END). >> >> I think it would make sense to refresh the inode size on media change >> so that even open file descriptors see the new size and a single >> process cannot force a stale value for all other userspace processes >> on the system. > > Hmmm... I don't know. ?Maybe we can but I'm not sure whether there's a > good reason for it. ?cdrom is locked while opened after all. ?Are > there actual problems? Yeah, sorry I didn't explain what the use case was. With QEMU you can pass through the physical CD-ROM into the virtual machine. QEMU opens /dev/cdrom with O_NONBLOCK | O_RDONLY. The guest can test if the medium is present and QEMU will do ioctl(fd, CDROM_DRIVE_STATUS, CDSL_CURRENT). The guest can also lock the tray and eject, again using the respective ioctls. Read operations are serviced by performing a read on the file descriptor in QEMU. And finally the medium size is queried by QEMU using lseek(fd, 0, SEEK_END). Today QEMU cannot keep /dev/cdrom open across media change because it will have an outdated inode size returned from lseek(fd, 0, SEEK_END). But if the cdrom driver (or sr) refresh the inode size on media change then there is no need to work around this from userspace. Stefan -- 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/