Re: [Xen-devel] Re: [PATCH] libxl: initialize domid to 0 in libxl__create_stubdom

[ZhouPeng <zpengxen@xxxxxxxxx>]

Thanks for your reply.

If do_domctl is the necessary path for every dom creation,
it seems allow to specify a domid for
the hypercall do_domctl: XEN_DOMCTL_createdomain

The refered code:
do_domctl(XEN_GUEST_HANDLE(xen_domctl_t) u_domctl)

    case XEN_DOMCTL_createdomain:
    {
        struct domain *d;
        domid_t        dom;
        static domid_t rover = 0;
        unsigned int domcr_flags;

        ret = -EINVAL;
        ...
        dom = op->domain;
        /*** here below, it seem to allow specify domid by caller ***/
        if ( (dom > 0) && (dom < DOMID_FIRST_RESERVED) )
        {
            ret = -EINVAL;
            if ( !is_free_domid(dom) )
                break;
        }
        else
        {
            for ( dom = rover + 1; dom != rover; dom++ )
            {
                if ( dom == DOMID_FIRST_RESERVED )
                    dom = 0;
                if ( is_free_domid(dom) )
                    break;
            }

            ret = -ENOMEM;
            if ( dom == rover )
                break;

            rover = dom;
        }

If it's true for this hypercall,
it's that the current tool's implementation hide it.

On Tue, Jun 21, 2011 at 8:28 PM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> ZhouPeng writes ("Re: [Xen-devel] Re: [PATCH] libxl: initialize domid to 0 in 
> libxl__create_stubdom"):
>> I think it should be both an input and output parameter,
>> which allows caller/user to provide a given domid,
>> if the given domid <= 0, it meas to request the hypervisor
>> to assign the next free id.
>
> This is not correct.  The hypervisor will always assign the domid and
> there is no facility to specify one.
>
> Ian.
>



-- 
Zhou Peng
Operating System Technology Group
Institute of Software, the Chinese Academy of Sciences (ISCAS)

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