Re: [PATCH] tools: libxc: do not redefine evtchn_port_or_error_t in xc_evtchn_compat.c

[Ian Campbell <ian.campbell@citrix.com>]

Adding Olaf, I forgot that Reported-by doesn't turn into a Cc.

On Thu, 2016-02-04 at 10:15 +0000, Ian Campbell wrote:
> This file stradles the xenevtchn and libxc evtchn_compat worlds, and
> hence ends up with two evtchn_port_or_error_t typedefs which older
> gcc's (and the C standard) do not like.
> 
> Avoid this by gating the compat definition on a gate provided by the
> compat implementation.
> 
> Note that this would still be broken by an application which does:
>     #define XC_WANT_COMPAT_EVTCHN_API
>     #include <xenevtchn.h>
>     #include <xenctrl.h>
> 
> Which effectively means that an application must be ported over to
> xenevtchn in one go rather than incrementally (e.g. if it uses
> evtchn's for multiple purposes). Since the port is actually fairly
> mechanical I hope this is acceptable.
> 
> Reported-by: Olaf Hering <olaf@aepfle.de>
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> I'm not super happy about this approach, due to the caveat in the
> second half of the commit message.
> 
> Other approaches:
> 
> rename the libxenevtchn type, e.g.  xenevtchn_port_or_error_t?

Thinking about this some more this might be the best approach. The type is
not used by qemu-xen, it is used by qemu-xen-traditional but we can fix
that in lockstep.

All of the in tree users are easy, of course.

Thoughts?

> 
> Some sort of skank based on the header guard #defines, but that's
> awful (and fragile).
> ---
>  tools/libxc/include/xenctrl_compat.h | 2 ++
>  tools/libxc/xc_evtchn_compat.c       | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/tools/libxc/include/xenctrl_compat.h
> b/tools/libxc/include/xenctrl_compat.h
> index 93ccadb..afc3d88 100644
> --- a/tools/libxc/include/xenctrl_compat.h
> +++ b/tools/libxc/include/xenctrl_compat.h
> @@ -51,7 +51,9 @@ void *xc_map_foreign_bulk(xc_interface *xch, uint32_t
> dom, int prot,
>  #ifdef XC_WANT_COMPAT_EVTCHN_API
>  
>  typedef struct xenevtchn_handle xc_evtchn;
> +#ifndef XC_BUILDING_COMPAT_EVTCHN_API
>  typedef xc_evtchn_port_or_error_t evtchn_port_or_error_t;
> +#endif
>  
>  xc_evtchn *xc_evtchn_open(xentoollog_logger *logger,
>                               unsigned open_flags);
> diff --git a/tools/libxc/xc_evtchn_compat.c
> b/tools/libxc/xc_evtchn_compat.c
> index 5d3e4ba..99da476 100644
> --- a/tools/libxc/xc_evtchn_compat.c
> +++ b/tools/libxc/xc_evtchn_compat.c
> @@ -6,6 +6,7 @@
>  #include <xenevtchn.h>
>  
>  #define XC_WANT_COMPAT_EVTCHN_API
> +#define XC_BUILDING_COMPAT_EVTCHN_API
>  #include "xenctrl.h"
>  
>  xc_evtchn *xc_evtchn_open(xentoollog_logger *logger,

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