Re: [PATCH] test: fix 'make assets' failure as root

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 25 Sep 2025 11:27:49 +0100
"Richard W.M. Jones" <rjones@redhat.com> wrote:

> On Thu, Sep 25, 2025 at 11:40:25AM +0200, Stefano Brivio wrote:
> > On Thu, 25 Sep 2025 09:53:06 +0100
> > "Richard W.M. Jones" <rjones@redhat.com> wrote:
> >   
> > > On Thu, Sep 25, 2025 at 01:43:06PM +0800, Yumei Huang wrote:  
> > > > Running `make assets` under `test` as root fails with a "Permission denied"
> > > > error when `prepare-distro-img.sh` invokes `virt-edit` and `guestfish`. This
> > > > is due to a known bug in libvirt.
> > > > 
> > > > Work around the issue by switching to the direct backend.
> > > > 
> > > > Signed-off-by: Yumei Huang <yuhuang@redhat.com>
> > > > ---
> > > >  test/prepare-distro-img.sh | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/test/prepare-distro-img.sh b/test/prepare-distro-img.sh
> > > > index 0d967c9..423eea7 100755
> > > > --- a/test/prepare-distro-img.sh
> > > > +++ b/test/prepare-distro-img.sh
> > > > @@ -3,6 +3,8 @@
> > > >  IMG="$1"
> > > >  PASST_FILES="$(echo ../*.c ../*.h ../*.sh ../*.1 ../Makefile ../README.md)"
> > > >  
> > > > +export LIBGUESTFS_BACKEND=direct    
> > > 
> > > Please add a comment that this is only added as a temporary hack until
> > > we can get a proper fix (in libguestfs possibly, see Dan's earlier
> > > email).  
> > 
> > On the other hand, regardless of that fix, I would be happy to be run
> > this on single-user Alpine L1 guests, eventually, where libguestfs
> > doesn't depend on libvirt (see my caveat 2.), and I usually reserve
> > very little disk space for those.  
> 
> The upstream default is backend 'direct'.  In Fedora & RHEL we
> override this with 'libvirt':
> 
> https://src.fedoraproject.org/rpms/libguestfs/blob/rawhide/f/libguestfs.spec#_714

Ah, sorry, I had no idea!

> I don't know what Alpine does, but likely it leaves it at the default.
> (You can try: `guestfish get-backend`)

Yes, this is guestfs-tools and libguestfs 1.56.1-r0 on Alpine:

  # guestfish get-backend
  direct

Same on any modern Debian, openSUSE, Ubuntu.

> > If you don't have compelling reasons (like you're dropping
> > LIBGUESTFS_BACKEND=direct in two weeks), I would simply keep this as
> > long as it works. The day you drop that, we'll drop this too.  
> 
> We're not dropping the environment variable / feature ever.  The
> problem is that this was cargo-culted into a lot of code over the
> years, and it does reduce the security of libguestfs on RHEL.  We're
> having an (ongoing) battle to remove this cargo-culting from CNV right
> now.  I'm just not keen to add this line in new places, without at
> least a comment saying this is a temporary hack, and not generally
> recommended.

Oh, I see, that makes sense.

But then, Yumei, we should also add to that comment (sorry, this is
becoming much more complicated than I thought...) that the workaround
is for Fedora and related distributions.

-- 
Stefao