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From: "Durrant, Paul" <pdurrant@amazon.co.uk>
To: Ian Jackson <ian.jackson@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"jandryuk@gmail.com" <jandryuk@gmail.com>,
	George Dunlap <George.Dunlap@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Anthony Perard <anthony.perard@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v3 4/6] libxl: allow creation of domains with a specified or random domid
Date: Fri, 17 Jan 2020 12:06:55 +0000
Message-ID: <d5ca972f0e7a429d847a522e9f21c54b@EX13D32EUC003.ant.amazon.com> (raw)
In-Reply-To: <24097.39947.159860.741920@mariner.uk.xensource.com>

> -----Original Message-----
> From: Ian Jackson <ian.jackson@citrix.com>
> Sent: 17 January 2020 12:36
> To: Durrant, Paul <pdurrant@amazon.co.uk>
> Cc: xen-devel@lists.xenproject.org; Wei Liu <wl@xen.org>; Anthony Perard
> <anthony.perard@citrix.com>; Andrew Cooper <Andrew.Cooper3@citrix.com>;
> George Dunlap <George.Dunlap@citrix.com>; Jan Beulich <jbeulich@suse.com>;
> Julien Grall <julien@xen.org>; Konrad Rzeszutek Wilk
> <konrad.wilk@oracle.com>; Stefano Stabellini <sstabellini@kernel.org>;
> jandryuk@gmail.com
> Subject: RE: [PATCH v3 4/6] libxl: allow creation of domains with a
> specified or random domid
> 
> Durrant, Paul writes ("RE: [PATCH v3 4/6] libxl: allow creation of domains
> with a specified or random domid"):
> > [Ian:]
> > > I think there are only two possible solutions:
> > >
> > >   - Check the domain's entry in the recent list *after* creating
> > >     the domain in Xen.  This involves accepting that we will
> > >     reuse the domid but only for a domain we are in the early
> > >     stages of constructing, so hopefully without bad consequence?
> > >
> > >   - Take the recent domid lock.
> > >
> >
> > Or take a global file lock in libxl around domain creation and
> destruction?
> 
> We want domain construction to be concurrent, when it can be.  So I
> think a lock around just xc_domain_create is OK but a lock around the
> whole operation is not.
> 
> > > Also, it seems to me that we should check the recent domid list if we
> > > let Xen choose the domid.  Maybe that can be in a subsequent patch...
> >
> > Well, we could solve all this, remove the need for a file and all the
> associated complexity by simply keeping history inside the hypervisor. I
> don't know how the Xen maintainers will feel about that though, as Xen
> itself shouldn't have a problem with eager domid re-use.
> 
> I think this doesn't need to be done in the hypervisor so I am
> inclined to say it shouldn't be.  Also, there is a lot of policy here...
> 

Ok, to cover all bases then it seems like checking the domid after creation and then destroying if it is too recent is the better option.

  Paul

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Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  9:35 [Xen-devel] [PATCH v3 0/6] xl/libxl: domid allocation/preservation changes Paul Durrant
2020-01-16  9:35 ` [Xen-devel] [PATCH v3 1/6] libxl: add definition of INVALID_DOMID to the API Paul Durrant
2020-01-16  9:35 ` [Xen-devel] [PATCH v3 2/6] libxl_create: make 'soft reset' explicit Paul Durrant
2020-01-16  9:35 ` [Xen-devel] [PATCH v3 3/6] libxl: add infrastructure to track and query 'retired' domids Paul Durrant
2020-01-16 18:27   ` Ian Jackson
2020-01-17  9:26     ` Durrant, Paul
2020-01-17 11:31       ` Ian Jackson
2020-01-16  9:36 ` [Xen-devel] [PATCH v3 4/6] libxl: allow creation of domains with a specified or random domid Paul Durrant
2020-01-16  9:40   ` Jan Beulich
2020-01-16  9:46     ` Durrant, Paul
2020-01-16  9:59       ` Jan Beulich
2020-01-16 15:53   ` Jason Andryuk
2020-01-16 18:36   ` Ian Jackson
2020-01-17  9:37     ` Durrant, Paul
2020-01-17 11:35       ` Ian Jackson
2020-01-17 12:06         ` Durrant, Paul [this message]
2020-01-17 15:30           ` Ian Jackson
2020-01-20  8:18             ` Durrant, Paul
2020-01-16  9:36 ` [Xen-devel] [PATCH v3 5/6] xl.conf: introduce 'domid_policy' Paul Durrant
2020-01-16 18:37   ` Ian Jackson
2020-01-16  9:36 ` [Xen-devel] [PATCH v3 6/6] xl: allow domid to be preserved on save/restore or migrate Paul Durrant
2020-01-16 18:39   ` Ian Jackson
2020-01-16 18:43 ` [Xen-devel] [PATCH v3 0/6] xl/libxl: domid allocation/preservation changes Ian Jackson
2020-01-17  9:11   ` Durrant, Paul

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