Re: [Xen-devel] Regression building HVM domains following "x86: add bitmap of enabled emulated devices"

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Nov 11, 2015 at 09:07:34PM +0000, Andrew Cooper wrote:
> On 11/11/2015 20:57, Konrad Rzeszutek Wilk wrote:
> > On Wed, Nov 11, 2015 at 07:13:25PM +0000, Andrew Cooper wrote:
> >> Hello,
> >>
> >> Xapi uses the Ocaml stub_xc_domain_create() which uses
> >> xc_domain_create().  xc_domain_create() itself zeros the arch
> >> configuration but passes flags straight through.
> > Ooops.
> >> As a result of c/s 171946ab "x86: add bitmap of enabled emulated
> >> devices", xc_domain_create() can no longer be used to construct HVM
> >> domains, failing the hypervisor-side sanity check.
> >>
> >> Needless to say, this has put a dent in XenServer's automated testing.
> >>
> >>
> >> There are a couple of options, but neither of them are fantastic.
> >>
> >> 1) Have xc_domain_create() fill in XEN_X86_EMU_ALL based on
> >> XEN_DOMCTL_CDF_hvm_guest and XEN_DOMCTL_CDF_pvh_guest
> >>
> >> or
> >>
> >> 2) Mandate that all callers provide a valid arch configuration,
> >> essentially turning xc_domain_create() into xc_domain_create_config()
> >>
> >>
> >> Longterm, what is the plan wrt guest construction?  With my x86
> >> maintainership hat on, I don't want to keep XEN_DOMCTL_CDF_pvh_guest in
> >> the interface, so I do not like 1) as an option.
> >>
> >> `git grep` indicates that the 3 users of xc_domain_create() are the
> >> Ocaml/Python stubs and init-xenstore-domain.c which only constructs a PV
> >> guest (which bypasses the issue), whereas libxl uses
> >> xc_domain_create_config().  (For the python stubs, I expect this will
> >> hit Oracle who are still using Xend to my knowledge).
> > We are moving to 'xl'.. and there are no Xend bits anymore.
> >> Option 2) is a better alternative, but will have a knock-on effect for
> >> downstream consumers of the stubs.
> > But aren't xc_* calls not-release-stable?
> 
> They are indeed not, which offers the option to change the API.
> 
> >
> > Here is a third idea::
> >
> >  Make 'xc_domain_create' call 'xc_domain_create_config'. The 
> > xc_domain_create
> >  would synthesis the flags and we would put an 'deprecated' flag on it
> >  (whatever that means?) and remove 'xc_domain_create' in 4.7?
> 
> This is option 1.  xc_domain_create() already calls
> xc_domain_create_config() but with a zeroed arch configuration.

When I wrote 'flag' I mean 'arch'. Sorry about that brainfart.
> 
> The issue is that modifying xc_domain_create() will preclude their
> construction of DMLite domains.

/me nods.
> 
> ~Andrew
> 
> >
> >> It is a worthwhile disruption?  I can't spot a compatible option which
> >> preserves the stubs' ability to build DMLite domains.
> >>
> >> ~Andrew
> 

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