[PATCH v2 2/2] qemu: Tell secdrivers which images are top parent

[Peter Krempa]

On Mon, Mar 09, 2020 at 13:39:56 +0100, Michal Privoznik wrote:
> On 3/9/20 10:18 AM, Peter Krempa wrote:
> > On Mon, Mar 09, 2020 at 09:29:43 +0100, Michal Privoznik wrote:
> > > When preparing images for block jobs we modify their seclabels so
> > > that QEMU can open them. However, as mentioned in the previous
> > > commit, secdrivers base some it their decisions whether the image
> > > they are working on is top of of the backing chain. Fortunately,
> > > in places where we call secdrivers we know this and the
> > > information can be passed to secdrivers.
> > > 
> > > The problem is the following: after the first blockcommit from
> > > the base to one of the parents the XATTRs on the base image are
> > > not cleared and therefore the second attempt to do another
> > > blockcommit fails. This is caused by blockcommit code calling
> > > qemuSecuritySetImageLabel() over the base image, possibly
> > > multiple times (to ensure RW/RO access). A naive fix would be to
> > > call the restore function. But this is not possible, because that
> > > would deny QEMU the access to the base image.  Fortunately, we
> > > can use the fact that seclabels are remembered only for the top
> > > of the backing chain and not for the rest of the backing chain.
> > > And thanks to the previous commit we can tell secdrivers which
> > > images are top of the backing chain.
> > > 
> > > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1803551
> > > 
> > > Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> > > ---
> > 
> > Once you fix all of the wrong variable name in this patch as well as in
> > the previous one:
> 
> Does isParentChainTop sound good for the variable name?

IMO isChainTop should be enough.