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$Id$
virt-df is a 'df' tool for printing out the used and available disk
space in all active and inactive domains. Without this tool you would
need to log in to each domain individually or set up monitoring.
It is only a proof-of-concept. Please bare in mind the following
limitations when using this tool:
(1) It does not work over remote connections. Part of the reason why
I wrote virt-df was to get an idea of how the remote storage API for
libvirt might look.
(2) It only understands a limited set of partition types. Assuming
that the files and partitions that we get back from libvirt / Xen
correspond to block devices in the guests, we can go some way towards
manually parsing those partitions to find out what they contain. We
can read the MBR, LVM, superblocks and so on. However that's a lot of
parsing work, and currently there is no library which understands a
wide range of partition schemes and filesystem types (not even
libparted which doesn't support LVM yet). The Linux kernel does
support that, but there's not really any good way to access that work.
The current implementation uses a hand-coded parser which understands
some simple formats (MBR, LVM2, ext2/3). In future we should use
something like libparted.
(3) The statistics you get are delayed. The real state of, for
example, an ext2 filesystem is only stored in the memory of the
guest's kernel. The ext2 superblock contains some meta-information
about blocks used and free, but this superblock is not up to date. In
fact the guest kernel may not update it even on a 'sync', not until
the filesystem is unmounted. Some operations do appear to write the
superblock, for example fsync(2) [that is my reading of the ext2/3
source code at least].
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