[libvirt] [ANNOUNCE] virt-df 2.1.0 - a 'df' tool for virtual guests

[Richard W.M. Jones]

On Thu, May 15, 2008 at 02:54:53PM +0100, Daniel P. Berrange wrote:
> > This version supports most common filesystems and partitioning
> > schemes, including:
> >  - Linux ext2/3
> >  - DOS FAT32
> >  - Windows NTFS
> >  - Linux LVM2 (volume groups and logical volumes)
> >  - Primary and extended disk partitions
> >  - Linux swap
> >  - Linux suspend partition
> 
> I'm assuming this only works for raw file & block devices ? Are you planning
> to support the funky QCow / VMDK formats too ?

Yes, interesting point.  Since I always use flat files or straight
partitions for my guests I admit I hadn't given this much thought :-)
However support for these formats is just a matter of decoding enough
of the structure to enable the same mappings to be made in the
'virt-df' library, same as for LVM2 or indeed MBR partitions now.

I'll take a look at it.  IIRC there are several different undocumented
variations on the QCow format?

> The other thing that could be annoying is that Fedora 9 support for
> encrypting all volumes - might need to prompt for a decryption key
> for that.

Yes -- any encrypted volumes aren't going to work at the moment, and
couldn't work unless there was a way to access the passphrase.

> > Included also is an experimental command line tool called 'diskzip'
> > which intelligently compresses disk images by leaving out the bits
> > which aren't actually used in the filesystems / partitions / volume
> > groups contained within.
> 
> That's pretty neat. Which file systems does that work for ?   VMWare have
> a funky  guest tool which tries to let you get to a similar point. It works
> by basically openning a file inside the guest VM and filling it with zeros
> until the entire disk is full. THeir backend can then detect and discard
> all the sectors with zeros. Understanding the filesystem metdata is a much
> nicer way todo this :-)

It works with most of the formats supported by virt-df.  For MBR & LVM
once you've parsed the partition tables / LVM metadata, then the
information you need just falls out naturally.  For NTFS & DOS FAT
(you won't believe it but ...) you need to find the allocation
bitmaps/tables in both cases in order to calculate blocks used/free
for df anyway.  For ext2 it's a little bit more tricky because one
needs to additionally parse the group block free bitmaps [this bit
doesn't work at the moment, but is in principle very simple to add].

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://et.redhat.com/~rjones/virt-top