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Re: [Xen-devel] [OSSTEST PATCH 4/9] mg-schema-test-database: Borrow shares properly

On Thu, 2015-12-17 at 17:43 +0000, Ian Jackson wrote:
> Ian Campbell writes ("Re: [OSSTEST PATCH 4/9] mg-schema-test
> -database: Borrow shares properly"):
> > On Thu, 2015-12-17 at 17:06 +0000, Ian Jackson wrote:
> > >   # As we copy, we note everything we're not borrowing as
> > > - # belonging to the parent db.
> > > + # belonging to the parent db.  We borrow shares of a
> shared
> > > + # resource.  If we borrow only some rather than all of
> the
> > > + # shares, neither DB will be able to unshare it.
> > 
> > This is what actually happens, rather than this comment explaining
> a thing
> > we are avoiding, right?
> Yes.
> > I ask because although the text (and the use of "properly" in the subject)
> > seems pretty clear it's the former I was surprised to find this code was
> > borrowing partial shares and therefore setting up such a situation. Given
> > the caveat below would it not be better to just never allow this?
> I have added this to the commit message:
>  Previously, the test database would be generated in a broken state:
>  resources share-host/foo/{1,2,...} exist but the resource host/foo/0
>  is allocated to magic/xdbref rather than to magic/shared.  This causes
>  various resource allocation machinery to crash.  (Even if the host is
>  entirely un-borrowed.)
> I guess it might be possible for mg-schema-test-database to check that
> either none or all of the shares of a host are being borrowed, but I
> don't think it's worth it.  The osstest git hash in the sharetype will
> in practice mostly prevent undesirable sharing of the same resource
> between test and real db instances.
> > I suppose that given the list of tasks to borrow came from the user
> > this might be considered a "keep both pieces" situation.
> Yes.  This partial sharing can only affect you if you have allocated
> individual shares to the task you say you want to borrow from.

Grand, with the extra commit log bit from above:
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

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