Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757635Ab1DHQwO (ORCPT ); Fri, 8 Apr 2011 12:52:14 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:42511 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757203Ab1DHQwN (ORCPT ); Fri, 8 Apr 2011 12:52:13 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=CSiOfj417zxCIkdtlRL0am2VCHbSYXB9Jh+Fkui9ChR0o6DyxSNWjMcrGa4pxuhL7D NQREcColUoKaWEhKqCLgo4DRcoePb4f4VDBKQq0msVvChbbRK0cZg2PJM+CoY65vcqmi PvfAhA+4i5sDzWg+aubXfKYBRhCcVgdcSFDRk= Date: Fri, 8 Apr 2011 09:52:07 -0700 From: Tejun Heo To: Stefan Hajnoczi Cc: Amit Shah , linux-kernel@vger.kernel.org, Jens Axboe , "James E.J. Bottomley" , linux-scsi@vger.kernel.org, Markus Armbruster Subject: Re: [PATCH] sr: Ensure disk is revalidated when media changes Message-ID: <20110408165207.GD3871@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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1791 Lines: 43 Hello, On Fri, Apr 08, 2011 at 05:43:16PM +0100, Stefan Hajnoczi wrote: > >> 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. Hmmm... ISTR there was some discussion about changing inode size on the fly quite a while ago. I didn't follow the discussion but it seemed to have rather nasty/delicate implications. Jens, any ideas? Thanks. -- tejun -- 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/