From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:34996) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TN3aN-0006LS-RK for qemu-devel@nongnu.org; Sat, 13 Oct 2012 11:25:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TN3aM-0006pM-Gl for qemu-devel@nongnu.org; Sat, 13 Oct 2012 11:25:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27188) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TN3aM-0006jL-7J for qemu-devel@nongnu.org; Sat, 13 Oct 2012 11:25:06 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q9DFP3Ak021570 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sat, 13 Oct 2012 11:25:04 -0400 Message-ID: <507987CE.5020708@redhat.com> Date: Sat, 13 Oct 2012 11:25:02 -0400 From: Jeff Cody MIME-Version: 1.0 References: <37ca1a150224c144f9329fc8408f78c388f50a02.1349848348.git.jcody@redhat.com> <50789120.2020805@redhat.com> In-Reply-To: <50789120.2020805@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] block: make bdrv_find_backing_image compare canonical filenames Reply-To: jcody@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org On 10/12/2012 05:52 PM, Eric Blake wrote: > On 10/09/2012 11:56 PM, Jeff Cody wrote: >> Currently, bdrv_find_backing_image compares bs->backing_file with >> what is passed in as a backing_file name. Mismatches may occur, >> however, when bs->backing_file and backing_file are both not >> absolute or relative. >> >> Use path_combine() to make sure any relative backing filenames are >> relative to the current image filename being searched, and then use >> realpath() to make all comparisons based on absolute filenames. >> >> This also changes bdrv_find_backing_image to no longer be recursive, >> but iterative. >> >> Signed-off-by: Jeff Cody >> --- >> block.c | 38 ++++++++++++++++++++++++++++++++------ >> 1 file changed, 32 insertions(+), 6 deletions(-) >> > >> + for (curr_bs = bs; curr_bs->backing_hd; curr_bs = curr_bs->backing_hd) { >> + /* If not an absolute filename path, make it relative to the current >> + * image's filename path */ >> + path_combine(filename_tmp, sizeof(filename_tmp), >> + curr_bs->filename, backing_file); > > I just realized that it is possible to set up a qcow2 file that wraps a > network protocol as its backing source, such as 'nbd:...'. In this > case, what does path_combine() do to that user string? > >> + >> + /* We are going to compare absolute pathnames */ >> + if (!realpath(filename_tmp, filename_full)) { >> + continue; >> + } > > and realpath() certainly won't like it (most likely, it won't exist in > the file system, but on the off chance that it does, that file is much > different than the real protocol that we are using as the backing source). > > I'm afraid you may need a followup patch that handles the case of a > non-file backing protocol, and insist on an exact match in that case > without trying any normalization. > Yes, it will need a follow-up patch. Check for protocol (path_has_protocol()), and if true just compare unmodified backing_file names, other wise use path_combine + realpath().