Re: [Xen-devel] [PATCH] libxl: fix assertion failure in stub domain creation

From: "Durrant, Paul" <pdurrant@amazon.co.uk>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>, "Wei Liu" <wl@xen.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH] libxl: fix assertion failure in stub domain creation
Date: Wed, 5 Feb 2020 10:50:46 +0000	[thread overview]
Message-ID: <822309f6c7ef4109b731d37efbad5793@EX13D32EUC003.ant.amazon.com> (raw)
In-Reply-To: <20200205104716.GA85066@perard.uk.xensource.com>

> -----Original Message-----
> From: Anthony PERARD <anthony.perard@citrix.com>
> Sent: 05 February 2020 10:47
> To: Durrant, Paul <pdurrant@amazon.co.uk>
> Cc: xen-devel@lists.xenproject.org; Ian Jackson
> <ian.jackson@eu.citrix.com>; Wei Liu <wl@xen.org>; Roger Pau Monné
> <roger.pau@citrix.com>
> Subject: Re: [PATCH] libxl: fix assertion failure in stub domain creation
> 
> On Wed, Feb 05, 2020 at 09:37:24AM +0000, Paul Durrant wrote:
> > An assertion in libxl__domain_make():
> >
> > 'soft_reset || *domid == INVALID_DOMID'
> >
> > does not hold true for stub domain creation, where soft_reset is false
> > but the passed in domid == 0. This is easily fixed by changing the
> > initializer in libxl__spawn_stub_dm().
> >
> > Fixes: 75259239d85d ("libxl_create: make 'soft reset' explicit")
> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> > ---
> >  tools/libxl/libxl_dm.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> > index f758daf3b6..3b1da90167 100644
> > --- a/tools/libxl/libxl_dm.c
> > +++ b/tools/libxl/libxl_dm.c
> > @@ -2127,7 +2127,7 @@ void libxl__spawn_stub_dm(libxl__egc *egc,
> libxl__stub_dm_spawn_state *sdss)
> >          goto out;
> >      }
> >
> > -    sdss->pvqemu.guest_domid = 0;
> > +    sdss->pvqemu.guest_domid = INVALID_DOMID;
> 
> How this works? INVALID_DOMID seems to be directly feed to
> xc_domain_create(), which is using XEN_DOMCTL_createdomain.
> But a comment in domctl.h for XEN_DOMCTL_createdomain read:
>     NB. xen_domctl.domain is an IN/OUT parameter for this operation.
>     If it is specified as zero, an id is auto-allocated and returned.
> So, is xc_domain_create going to create a new domain with
> domid==INVALID_DOMID?
> 

As it happens, no. That comment is wrong. It should read "If it is not set to a valid value, an id is auto-allocated and returned".

  Paul

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