Re: [Xen-devel] REST MAINTAINERS feedback requested Was:Re: [PATCH v5 01/28] HYPERCALL_version_op. New hypercall mirroring XENVER_ but sane.

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

On Mon, Apr 11, 2016 at 05:25:04PM +0100, Ian Jackson wrote:
> Jan Beulich writes ("Re: REST MAINTAINERS feedback requested Was:Re: 
> [Xen-devel] [PATCH v5 01/28] HYPERCALL_version_op. New hypercall mirroring 
> XENVER_ but sane."):
> > On 11.04.16 at 16:22, <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> > > But to an extent some of this conversation seems to be on matters of
> > > taste.
> > 
> > Agreed.
> > 
> > > Jan, what is the downside of introducing a new hypercall ?
> > 
> > Duplicate code effectively doing the same thing.
> 
> I agree that duplication is bad, all other things being equal.
> 
> But any improvement from an old API to a new one necessarily involves
> providing a dual facility during a transition period.
> 
> I don't see an explicit deprecation in the patch that is in tree, but
> it seems to me to be intended (and, perhaps, implied).  Certainly if

I tried it at some point by adding the suffix 'compat' to it.

The compat layer did not like the extra compat string and all kinds of
compilation issues arose. I put it on the backburner.

> we are going to permit these strings etc. to be bigger than fits in
> the old hypercall, the old hypercall needs to be deprecated on the
> grounds that it can provide incomplete or inaccurate information.

The build-id in Config.mk is set to use sha1. Which produces 20 bytes.
You (or anybody else) can modify Config.mk to modify --build-id
as per man ld (there is an uuid or md5 or):

 "0xhexstring" to use a chosen bit string specified as an even number of 
hexadecimal
  digits ("-" and ":" characters between digit pairs are ignored)."

which does not impose any limits. Albeit 2967 characters of 0xdeadbeef is all I 
seem to be able
jam on the line. Weird. Anyhow:

build_id               : 
deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeef0000deadbeefdeadbeef0000deadbeef0000deadbeef0000dead

is possible.

> 
> Does this way of looking at it help ?
> 
> Thanks,
> Ian.

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