Re: [Xen-devel] [PATCH XEN v8 02/29] tools: Refactor /dev/xen/evtchn wrappers into libxenevtchn.

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/25/2016 09:35 AM, Ian Jackson wrote:
> Ian Campbell writes ("Re: [Xen-devel] [PATCH XEN v8 02/29] tools: Refactor 
> /dev/xen/evtchn wrappers into libxenevtchn."):
> > Various of the tools/libs/*/include/*.h have a
> >
> >      /* Callers who don't care don't need to #include <xentoollog.h> */
> >      typedef struct xentoollog_logger xentoollog_logger;
> >
> > but since that typedef matches in all cases I think it is allowed to be
> > repeated like this, isn't it?
> No, I'm afraid not.  It is permitted to repeatedly mention `struct
> xentoollog_logger', but the typedef must only occur once in any
> translation unit.
>
> If it is desirable to let callers avoid including xentoollog.h, then
> all those headers need to say:
>
>    struct xentoollog_logger;
>    int some_function(..., struct xentoollog_logger *lg, ...);
>
> So in your patches something like:
>
>    struct xentoollog_logger;
>
>    xenevtchn_handle *xenevtchn_open(struct xentoollog_logger *logger,
>                                     unsigned open_flags);
>
> The separate `struct xentoollog_logger;' is needed because otherwise
> the `struct xentoollog_logger *logger' in the formal parameters of
> xenevtchn_open is a declaration, rather than a reference to a
> previously-declared thing, and if it is a declaration its scope is
> only the contained function prototype, so other mentions of `struct
> xentoollog_logger' are treated as references to a different type.
> This is, of course, insane.
(I was just about to respond to IanC's earlier message)

It builds on my desktop (gcc 4.9.2) but not on an older setup (4.4.7). 
BTW, I should have explicitly said so: I haven't bisected to this commit 
--- it just looked like this ould be the culprit.
-boris

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