From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:51670 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235Ab3CRJ1G (ORCPT ); Mon, 18 Mar 2013 05:27:06 -0400 Date: Mon, 18 Mar 2013 10:27:00 +0100 From: Karel Zak To: Jeff Mahoney Cc: util-linux@vger.kernel.org Subject: Re: [PATCH] loopdev: sync capacity after setting it Message-ID: <20130318092700.GC2172@x2.net.home> References: <51438CF9.7020707@suse.com> <5145D0B4.1070207@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <5145D0B4.1070207@suse.com> Sender: util-linux-owner@vger.kernel.org List-ID: On Sun, Mar 17, 2013 at 10:18:28AM -0400, Jeff Mahoney wrote: > On 03/15/2013 05:04 PM, Jeff Mahoney wrote: > >I recently tried to mount an hfsplus file system from an image file with > >a partition table by using the loop offset and sizelimit options to specify > >the location of the file system. > > > >hfsplus stores some metadata at a set offset from the end of the partition, > >so it's sensitive to the device size reported by the kernel. > > > >It worked with this: > ># losetup -r -o 32k --sizelimit=102400000 > ># mount -r -t hfsplus > > > >But failed with this: > ># mount -r -oloop,offset=32k,sizelimit=102400000 > > > ># losetup -a > >/dev/loop0: [0089]:2 (), offset 32768, sizelimit 102400000 > >/dev/loop1: [0089]:2 (), offset 32768, sizelimit 102400000 > > > >/proc/partitions shows the correct number of blocks to match the sizelimit. > > > >But if I set a breakpoint in mount before the mount syscall, I could see: > ># blockdev --getsize64 /dev/loop[01] > >102400000 > >102432768 > > > >The kernel loop driver will set the gendisk capacity of the device at > >LOOP_SET_STATUS64 but won't sync it to the block device until one of two > >conditions are met: All open file descriptors referring to the device are > >closed (and it will sync when re-opened) or if the LOOP_SET_CAPACITY ioctl > >is called to sync it. Since mount opens the device and passes it directly > >to the mount syscall after LOOP_SET_STATUS64 without closing and reopening > >it, the sizelimit argument is effectively ignroed. The capacity needs to > >be synced immediately for it to work as expected. > > > >This patch adds the LOOP_SET_CAPACITY call to loopctx_setup_device since > >the device isn't yet released to the user, so it's safe to sync the capacity > >immediately. > > It turns out this ioctl wasn't introduced until 2.6.30. I'll fix that up and > resend tomorrow. Do you mean #ifdef LOOP_SET_CAPACITY? I can fix the patch manually. (It seem that we already use this ioctl in code without any extra care about old kernel and nobody complains :-) Karel -- Karel Zak http://karelzak.blogspot.com