[Users] Why does vzctl not check dirty flag of ploop device?

[Roman Haefeli]

Hi all

We are running several CTs on a cluster of a few OpenVZ host nodes. The
nodes share an NFS export where the ploop images of the CTs are located.

I noticed that 'vzctl start CTID' will happily start a ploop-based CT
that is already running on a different node. This is also possible with
simfs-CTs (having their private directory on NFS), but running a
ploop-CT on two nodes at the same time severely corrupts the CTs
filesystem. Before deploying such a setup, I would like to much sure
that this is avoided by any chance.

I found that a ploop imagefile will set a 'dirty flag' when it is in
use. Why doesn't 'vzctl' take that into accout? If 'vzctl' would read
that flag on CT start and refuse to start the CT when it is dirty, it
would not be possible to start the same CT twice.

I would like 'vzctl start $CTID' to do something like this:

ploop-fsck -f -r /vz/private/$CTID/root.hdd/root.hdd && \
  vzctl start $CTID

What do you think?

Roman