Re: opening files in exclusive mode?

[Michael Tokarev <mjt@tls.msk.ru>]

Brian Jackson wrote:

> This has been discussed thoroughly on this list at least once in the
> past. It was decided against changing the default for various reasons.

Well, I understand points about changing defaults.  I disagree,
because it really hurts to have no warnings whatsoever when, by
a chance, running off an already used block device (it's even
possible to run a guest off a block device mounted on host!),
but that's another topic (I'll take a look at the archives).

> See the original thread for all the reasons, but the ones I remember
> are: it would kill backward compatibility for people that start multiple
> guests from the same source with -snapshot and for people who use qcow
> images with base images.

Well, qcow with base image is easy: there are shared and exclusive
locks out there.  Base image gets locked in shared mode, while the
qcow itself is in exclusive.

>  It was also suggested that this might be a
> feature better suited for a mgmt application since it likely has a
> better idea of who/how it will be used.

There is, so far, no management application.  I for one either run
kvm manually from command line, or use a shell script with a single
command line in it (because the command line becomes quite long).
And it seems most people who experiment with kvm are either doing
the same or are trying libvirt and falling back to bare command line
when that does not work.  So that "management application" becomes
the human who runs the whole thing, and who needs this whole feature
in the first place... :)

>  It could also disrupt live
> migration.

That's probably true.  Again, with some workarounds, or disabling
locking.. I dunno for now.

But the question stands: how about the whole idea about PROVIDING
such an option, to start with?

Thanks!

/mjt