From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from cantor2.suse.de ([195.135.220.15]:53829 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932316Ab3COVFC (ORCPT ); Fri, 15 Mar 2013 17:05:02 -0400 Received: from relay1.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 7F156A4386 for ; Fri, 15 Mar 2013 22:05:01 +0100 (CET) Message-ID: <51438CF9.7020707@suse.com> Date: Fri, 15 Mar 2013 17:04:57 -0400 From: Jeff Mahoney MIME-Version: 1.0 To: util-linux@vger.kernel.org Subject: [PATCH] loopdev: sync capacity after setting it Content-Type: text/plain; charset=ISO-8859-1 Sender: util-linux-owner@vger.kernel.org List-ID: 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. Signed-off-by: Jeff Mahoney --- lib/loopdev.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- a/lib/loopdev.c +++ b/lib/loopdev.c @@ -1105,6 +1105,18 @@ int loopcxt_setup_device(struct loopdev_ goto err; } + /* + * mount passes the file descriptor without closing it, so + * the capacity isn't updated automatically. File systems + * won't see the new size if it's not the full size of + * the backing file. + */ + if ((lc->info.lo_offset || lc->info.lo_sizelimit) && + ioctl(dev_fd, LOOP_SET_CAPACITY, 0)) { + DBG(lc, loopdev_debug("LOOP_SET_CAPACITY failed: %m")); + goto err; + } + DBG(lc, loopdev_debug("setup: LOOP_SET_STATUS64: OK")); memset(&lc->info, 0, sizeof(lc->info)); -- Jeff Mahoney SUSE Labs