On 08/24/2011 12:19 PM, Pekka Enberg wrote:
On 8/24/11 11:31 AM, Avi Kivity wrote:
On 08/23/2011 08:08 AM, Pekka Enberg wrote:
As for changes, we've implemented rootfs over 9p with "kvm run"
booting to host filesystem "/bin/sh" by default.
Isn't this dangerous? Users expect virtualization to land them in
sandbox, but here an rm -rf / in the guest will happily junk the host
filesystem.
Not really because I never run the tool as root. However, you're right
that
we should not default to /bin/sh if you're root.
Well, just trashing /home/penberg would be bad too, no? (my recent
experience indicates it's not that catastrophic - anything important
sits on a server somewhere and the local data is just a cache).
Still dangerous (but just to the guest), since it's not a true
snapshot. If the host filesystem changes underneath the guest, it
will see partial and incoherent updates. Copy-on-write only works if
the host filesystem doesn't change.
That's a generic problem with overlayfs based solutions, isn't it?
We're planning
to use copy-on-write only on files that aren't supposed to change that
often -
like /usr and /lib.
So the guest won't see bad data that often?
Overlay works fine if the host tree is readonly. So if you have a
separate tree for guests, you can share it with any number of them.
Just don't share the host root.
Note this probably isn't a problem booting to /bin/bash, just booting a
full-featured guest with package management and other database-like apps
that expect exclusive control over their data.
I suppose we should force shared files to be read-only in
the guest.
Yes, that's safer.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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