[Libguestfs] Weird results from g.sh()

[Sam Eiderman]

I ended up with the following logic (which is pretty close to what you
suggested, had to unmount sysfs first to create directories there)

    def update(self, g):
        if self.boot_type == BootType.UEFI:
            # On rhel7 and sles12/15 the grub config is set to non efi commands
            # due to a weak uefi detection algorithm which doesn't work from a
            # chrooted environment (checks for [ -d /sys/firmware/efi ]).
            # libguestfs bind-mounts the sysfs of the appliance to /sys when
            # invoking g.sh()/command() - Therefore, /sys/firmware/efi does
            # not exist. Hack around this behavior by unmount /sys and
            # creating /sys/firmware/efi dir before running grub2's mkconfig.
            g.sh(f'umount /sys && mkdir -p /sys/firmware/efi && '
                 f'{self.mkconfig} -o {self.config}')
        else:
            g.command([self.mkconfig, '-o', self.config])
        return True

I'm pretty sure that should be fixed in virt-v2v too (although I'm a
bit lazy do write that OCaml equivalent of this and test it).
So just a heads up on the mailing list.

Sam

On Thu, Aug 27, 2020 at 12:28 PM Sam Eiderman <sameid at google.com> wrote:
>
> I see, thanks for the clarification.
>
> On Thu, Aug 27, 2020 at 12:05 PM Richard W.M. Jones <rjones at redhat.com> wrote:
> >
> > On Thu, Aug 27, 2020 at 11:24:57AM +0300, Sam Eiderman wrote:
> > > Yes, I understand that, I am just surprised to know that we bind /sys
> > > for g.sh() commands.
> > >
> > > However, "g.command([self.mkconfig, '-o', self.config])" shouldn't
> > > have the appliances /sys available (I looked briefly in command.c and
> > > I don't see the same bind-mount code), or maybe I'm missing something.
> >
> > guestfs_sh, guestfs_sh_lines, guestfs_command, guestfs_command_lines
> > all attempt to bind-mount /sys and other directories into the chroot
> > while running the command.  (See daemon/sh.c)
> >
> > Anyway I misunderstood before - I thought you were trying to run grub
> > to install the bootloader.  Running grub2-mkconfig as done in virt-v2v
> > should be fine since AIUI it's just concatenating some configuration
> > files together.
> >
> > > I thought I could use my g.mkdir_p('/sys/firmware/efi') hack, but
> > > since it didn't work, I'm now resort to explicitly handling this
> > > failure after running the mkconfig command:
> >
> > The mkdir didn't work since that directory will be covered by the bind
> > mount when the command is running.
> >
> > I'm not sure there's a good answer here, maybe something like:
> >
> >   g.sh ("
> >     mkdir -p /sys/firmware/efi
> >     # create some files in /sys/firmware/efi to trick grub
> >     grub2-mkconfig -o ...
> >   ")
> >
> > although this may modify the appliance's real /sys.
> >
> > Rich.
> >
> > --
> > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> > Read my programming and virtualization blog: http://rwmj.wordpress.com
> > libguestfs lets you edit virtual machines.  Supports shell scripting,
> > bindings from many languages.  http://libguestfs.org
> >