Re: [Xen-devel] [PATCH] tools/libxc: Provide evtchn_port_or_error_t for compat xenctrl interface

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 03/02/16 17:12, Olaf Hering wrote:
> On Mon, Feb 01, Andrew Cooper wrote:
>
>> c/s 2d2f789 "tools: rename libxc's evtchn_port_or_error_t with an xc_
>> prefix" doesn't cater for older applications which have requested
>> XC_WANT_COMPAT_EVTCHN_API
> Not sure, but I think this breaks staging at last in SLES11:
>
> [   93s] gcc  -DPIC -O1 -fno-omit-frame-pointer -m64 -fno-strict-aliasing 
> -std=gnu99 -Wall -Wstrict-prototypes -Wdeclaration-after-statement   -O0 -g3 
> -D__XEN_TOOLS__ -MMD -MF .xc_evtchn_compat.opic.d -D_LARGEFILE_SOURCE 
> -D_LARGEFILE64_SOURCE -fno-optimize-sibling-calls -D_GNU_SOURCE 
> -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector 
> -funwind-tables -fasynchronous-unwind-tables -I../../xen/common/libelf 
> -Werror -Wmissing-prototypes -I. -I./include 
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  -pthread 
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/toollog/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/evtchn/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  -include 
> /usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/config.h
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/call/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/foreignmemory/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/gnttab/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/gnttab/include
>  
> -I/usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/include
>   -fPIC -c -o xc_evtchn_compat.opic xc_evtchn_compat.c
> [   93s] In file included from ./include/xenctrl.h:2577,
> [   93s]                  from xc_evtchn_compat.c:9:
> [   93s] ./include/xenctrl_compat.h:54: error: redefinition of typedef 
> 'evtchn_port_or_error_t'
> [   93s] 
> /usr/src/packages/BUILD/xen-4.7.20160203T131200.be05b53/non-dbg/tools/libxc/../../tools/libs/evtchn/include/xenevtchn.h:31:
>  error: previous declaration of 'evtchn_port_or_error_t' was here
> [   93s] make[4]: *** [xc_evtchn_compat.opic] Error 1
>
> Olaf

Urgh.  This is getting even more complicated.

This patch is needed to avoid breaking the build for older programs
using just

#define XC_WANT_COMPAT_EVTCHN_API
#include <xenctrl.h>

so simply reverting it isn't a viable option either.

Is there any way in C to determine whether a typedef already exists?

~Andrew


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