[libvirt][PATCH RESEND v10 1/5] qemu: provide support to query the SGX capability

[Huang, Haibin]

I understand and thank you very much for your meticulous explanation.

> -----Original Message-----
> From: Michal Prívozník <mprivozn at redhat.com>
> Sent: Wednesday, February 23, 2022 8:16 PM
> To: Huang, Haibin <haibin.huang at intel.com>; libvir-list at redhat.com;
> berrange at redhat.com; Ding, Jian-feng <jian-feng.ding at intel.com>; Yang, Lin
> A <lin.a.yang at intel.com>; Lu, Lianhao <lianhao.lu at intel.com>
> Subject: Re: [libvirt][PATCH RESEND v10 1/5] qemu: provide support to query
> the SGX capability
> 
> On 2/23/22 04:41, Huang, Haibin wrote:
> > I accept all comments. But I didn't your point for this comment .
> >>> +static void
> >>> +virQEMUCapsFormatSGXInfo(virQEMUCaps *qemuCaps, virBuffer *buf)
> {
> >>> +    virSGXCapabilityPtr sgx =
> >>> +virQEMUCapsGetSGXCapabilities(qemuCaps);
> >>> +
> >>> +    virBufferAddLit(buf, "<sgx>\n");
> >>> +    virBufferAdjustIndent(buf, 2);
> >>> +    virBufferAsprintf(buf, "<flc>%s</flc>\n", sgx->flc ? "yes" :
> >>> + "no");
> >>
> >> ... which is in contradiction with the way we format it.
> > [Haibin] sorry, I don't get your point, can you give me the details
> >
> > Does you mean that change virBufferAsprintf(buf, "<flc>%s</flc>\n",
> > sgx->flc ? "yes" : "no"); to virBufferAsprintf(buf, "<flc>%u</flc>\n",
> > sgx->flc);
> 
> No. You can keep this particual virBufferAsprintf() as is. What I have problem
> with is the parsing side. So if this virQEMUCapsFormatSGXInfo() function is
> called, if produces the following XML:
> 
>   <sgx>
>     <flc>no</flc>
>     <epc_size>1024</epc_size>
>   </sgx>
> 
> (I've made the values up)
> 
> This corresponds to: sgx->flc = false; sgx->epc_size = 1024;
> 
> But when the XML is parsed, in virQEMUCapsParseSGXInfo(), it would se the
> following values:
> 
> sgx->flc = true; sgx->epc_size = 2014;
> 
> Notice the change in ->flc? This is because
> virXPathBoolean("boolean(./sgx/flc)") does not evaluate the value of <flc/>
> element, but only whether the xpath exists. Therefore, even if flc's element
> value is "no", it does exist and as such is evaluated to true.
> 
> Hope this cleans things up.
> 
> Michal