Re: libxenguest and xenguest.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.09.2020 10:06, Jürgen Groß wrote:
> On 15.09.20 09:55, Jan Beulich wrote:
>> On 15.09.2020 07:18, Jürgen Groß wrote:
>>> Andy has reported a libxenguest related build failure of qemu when
>>> building qemu outside the Xen build environment. Problem is xenguest.h
>>> now including xenctrl_dom.h, which is including xen/libelf/libelf.h.
>>>
>>> The underlying problem is that libxenguest is basically offering some
>>> "official" functions via xenguest.h, while some other functions are
>>> only Xen internally usable and are defined in xenctrl_dom.h.
>>>
>>> This is a rather weird construction and I'm seeing the following
>>> solutions:
>>>
>>> 1. Make xen/include/xen/libelf.h a public header (or split the parts
>>>      needed by xenguest.h into a public header)
>>
>> Besides being conceptually wrong imo, this could (afaict) cause name
>> space issues to consumers. This definitely gets a -1 from me, if not
>> a -2.
>>
>>> 2. Reflect the two parts of libxenguest by carving out the xenctrl_dom.h
>>>      defined parts into a new library not made public
>>>
>>> 3. Make the xenctrl_dom.h interfaces internal again by not adding it to
>>>      the installed headers
>>
>> This option would seem to imply that qemu has no real need to include
>> this header, as otherwise how would this address the build issue?
> 
> In fact qemu doesn't need to include xenguest.h at all, but this was
> just how the problem was discovered.
> 
> So before my patches xenctrl_dom.h (or xc_dom.h as it was named at that
> time) was included only from Xen sources (libxenguest, libxl, pvgrub).
> Basically there was a rather large part of libxenguest ot really usable
> by anyone outside the Xen build system. External users could use only
> the interfaces which are declared in xenguest.h.

But then - what did change?

In any event, to me it looks like headers shouldn't have mixed purpose.
Either they're internal (and don't get installed), or they're meant for
public consumption (and then everything that's in there).

Jan