From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [PATCH] tools: pygrub: if partition table is empty, try treating as a whole disk Date: Wed, 11 Nov 2015 14:57:51 +0000 Message-ID: <20151111145751.GD10274@zion.uk.xensource.com> References: <1446734772-27405-1-git-send-email-ian.campbell@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1446734772-27405-1-git-send-email-ian.campbell@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: wei.liu2@citrix.com, ian.jackson@eu.citrix.com, 745419-forwarded@bugs.debian.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Thu, Nov 05, 2015 at 02:46:12PM +0000, Ian Campbell wrote: > pygrub (in identify_disk_image()) detects a DOS style partition table > via the presence of the 0xaa55 signature at the end of the first > sector of the disk. > > However this signature is also present in whole-disk configurations > when there is an MBR on the disk. Many filesystems (e.g. ext[234]) > include leading padding in their on disk format specifically to enable > this. > > So if we think we have a DOS partition table but do not find any > actual partition table entries we may as well try looking at it as a > whole disk image. Worst case is we probe and find there isn't anything > there. > > This was reported by Sjors Gielen in Debian bug #745419. The fix was > inspired by a patch by Adi Kriegisch in > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=745419#27 > > Tested by genext2fs'ing my /boot into a new raw image (works) and > then: > dd if=/usr/lib/grub/i386-pc/g2ldr.mbr of=img conv=notrunc bs=512 count=1 > > to add an MBR (with 0xaa55 signature) to it, which after this patch > also works. > > Signed-off-by: Ian Campbell > Cc: 745419-forwarded@bugs.debian.org Acked-by: Wei Liu > --- > tools/pygrub/src/pygrub | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/tools/pygrub/src/pygrub b/tools/pygrub/src/pygrub > index e4aedda..40f9584 100755 > --- a/tools/pygrub/src/pygrub > +++ b/tools/pygrub/src/pygrub > @@ -156,6 +156,11 @@ def get_partition_offsets(file): > else: > part_offs.append(offset) > > + # We thought we had a DOS partition table, but didn't find any > + # actual valid partition entries. This can happen because an MBR > + # (e.g. grubs) may contain the same signature. > + if not part_offs: part_offs = [0] > + > return part_offs > > class GrubLineEditor(curses.textpad.Textbox): > -- > 2.1.4 >