From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH XEN v8 02/29] tools: Refactor
 /dev/xen/evtchn wrappers into libxenevtchn.
Date: Mon, 25 Jan 2016 14:35:22 +0000
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To: Ian Campbell <ian.campbell@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, wei.liu2@citrix.com, xen-devel@lists.xen.org
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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.

Ian.