[Libguestfs] libguestfs question - multiple partitions in the guest

[Shawn Kennedy]

> -----Original Message-----
> From: Richard W.M. Jones [mailto:rjones at redhat.com]
> Sent: Wednesday, August 01, 2012 2:54 PM
> To: Shawn Kennedy
> Cc: libguestfs at redhat.com; 'Smudde, Mark Alan (Mark)'; 'Tockstein, James E (Jim)'
> Subject: Re: [Libguestfs] libguestfs question - multiple partitions in the guest
> 
> On Wed, Aug 01, 2012 at 01:19:45PM -0500, Shawn Kennedy wrote:
> > Hi Richard,
> >
> > Because I have 2 filesystems (one in a mounted LV and one in a unmounted
> > LV), I get 2 sets of mountpoints in virt-inspector2 ....
> >
> >     <mountpoints>
> >       <mountpoint dev="/dev/VG1/LV0001.root">/</mountpoint>
> >       <mountpoint dev="/dev/VG1/LV0001.var">/var</mountpoint>
> >       <mountpoint dev="/dev/VG1/LV0001.app1">/app1</mountpoint>
> >       <mountpoint dev="/dev/sda1">/boot</mountpoint>
> >       <mountpoint dev="/dev/VG1/home">/home</mountpoint>
> >       <mountpoint dev="/dev/VG1/logs">/logs</mountpoint>
> >       <mountpoint dev="/dev/VG1/cores">/cores</mountpoint>
> >       <mountpoint dev="/dev/VG1/storage">/storage</mountpoint>
> >     </mountpoints>
> >
> >     <mountpoints>
> >       <mountpoint dev="/dev/VG1/LV0002.root">/</mountpoint>
> >       <mountpoint dev="/dev/VG1/LV0002.var">/var</mountpoint>
> >       <mountpoint dev="/dev/VG1/LV0002.app1">/app1</mountpoint>
> >       <mountpoint dev="/dev/sda1">/boot</mountpoint>
> >       <mountpoint dev="/dev/VG1/home">/home</mountpoint>
> >       <mountpoint dev="/dev/VG1/logs">/logs</mountpoint>
> >       <mountpoint dev="/dev/VG1/cores">/cores</mountpoint>
> >       <mountpoint dev="/dev/VG1/storage">/storage</mountpoint>
> >     </mountpoints>
> 
> virt-inspector is hopefully seeing two separate <operatingsystem>'s
> here.

Hi Rich, 

It is.  I took the liberty of snipping the output quite a bit.  I can send
more, but I don't think that's worth the effort knowing it does
see two OSs.
 
> > So, which one is the real one??  If I log into the guest directly,
> > I know the /dev/VG1/LV0002* is the mounted partition (by
> > using 'mount' command or by examining /etc/fstab).
> 
> So I think what you're asking is, what root device is currently
> mounted in the running guest, when you're inspecting the guest from
> outside (hopefully read-only) using libguestfs.

Oh yes - Read only, especially since it's a live running guest! :-)

> This isn't something that libguestfs can know since all it can see is
> what is in the disks, not the state of the running guest itself.  But
> there are some heuristics you could use instead:
> 
> (1) You could look at tell-tale signs to see which root device has
> most recently been mounted.  Probably the simplest thing is to look at
> the date of /var/log/messages in each potential root, and choose the
> most recent one (since /var/log/messages is reliably and frequently
> updated when a guest boots and runs).

That's a good idea - inspecting deeper into the guests' LV to see which
one is live by looking for data that could tell you that. /var/log/messages
is one way to know (timestamp of the file).

> (2) You could try doing what virt-v2v does, which is to parse the grub
> configuration to find out what root parameter is being passed to the
> kernel at boot time.  I believe this is the code ...
> 
> http://git.fedorahosted.org/git/?p=virt-
> v2v.git;a=blob;f=lib/Sys/VirtConvert/Converter/RedHat.pm;h=6bda68bffad6fc959dbadadee89447df71245491;hb=H
> EAD#l549

We will look into seeing what this is doing.  looking at the grub config
will be the most correct way.

I wonder - maybe an new tool (virt-grub) to dump out the grub
content of the guest image (if linux)!! :-) :-) :-)

As always, Thanks!
Shawn