Jeremy Fitzhardinge writes ("Re: xl create should refuse to share block devices
RW between domains"):
> Well, my specific use case is that I have pairs of domain configs, one
> PV, one HVM, referring to the same set of resources. I want xl create
> to catch when I try and create the PV version of a domain while the HVM
> is still running.
Mmm. Of course an HVM domain needs to open the underlying device
twice, once for blktap and once for qemu.
> A more comprehensive check would be nice, but just this would be
> useful. But whatever it does check should be 100% reliable.
Well, I guess I meant:
1. Do we have to catch every possible conflict ? If so then
your e2fsprogs example is one we need to consider, and we
will have to add a new kernel feature which can prevent e2fsprogs
from opening the block device, or simulate "mounting" it or
something.
1b. If not, then which conflicts are we trying to detect ?
2. If we catch a particular combination (eg, start two domains at
once using the same storage resources) does our check have to be
race-free ? That may make it more complicated - and if the answer
to my first question is "no" there will be some things which are
inherently racy (eg, spotting mounting a domain's disk
vs. starting a domain with a disk which is mounted).
NB that when we fix the bug that you can start multiple domains with
the same name, you'll be able to avoid your PV/HVM accident by
specifying the same name in each config file.
Ian.
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
Home