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[Xen-devel] Re: xl create should refuse to share block devices RW betwee

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: xl create should refuse to share block devices RW between domains
From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Date: Tue, 27 Jul 2010 16:17:52 +0100
Cc: "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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Jeremy Fitzhardinge writes ("xl create should refuse to share block devices RW 
between domains"):
>   When creating a domain, "xl create" should fail if a block device is 
> shared RW between domains, like xm create does.
> I'm not sure how this would be implemented.  Search xenstore for 
> references to the device when setting up a domain?

Does this safety catch have to be 100% reliable ?  If not then there
are some useful heuristics: for example, you could see whether the
device is a devmapper device and if so check its open count.  That
would catch simultaneously mounting the fs in dom0.

Doesn't the kernel already have some features to try to stop multiple
conflicting uses of the same block device ?  Perhaps blktap[2] should
do the same ?


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