Re: Regression building HVM domains following "x86: add bitmap of enabled emulated devices"

[Andrew Cooper <andrew.cooper3@citrix.com>]

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.

The issue is that modifying xc_domain_create() will preclude their
construction of DMLite domains.

~Andrew

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