[libvirt] main: fix some compilation issues on non-linux platforms

[Eric Blake]

On 08/16/2011 11:29 AM, Eric Blake wrote:
>> +++ b/src/util/virpidfile.c
>> @@ -213,6 +213,8 @@ int virPidFileReadPathIfAlive(const char *path,
>> #ifdef __linux__
>> if (virFileLinkPointsTo(procpath, binpath) == 0)
>> *pid = -1;
>> +#else
>> + (void)binpath;
>> #endif
>
> Here, I'd rather mark binpath as ATTRIBUTE_UNUSED than add the #else
> preprocessor conditional. That is, ATTRIBUTE_UNUSED means only that the
> variable might be unused, not that it can't be used (so used on linux,
> unused otherwise qualifies).

Food for a separate patch: I see no reason why virFileLinkPointsTo won't 
work on cygwin.  That is, the fact that we used #ifdef __linux__ is 
wrong, since cygwin also has a working /proc/pid/ file tree to determine 
if an executable is still valid; we should instead be doing #if 
PROCFS_AVAIL, along with some sort of configuration check that accepts 
both linux and cygwin procfs (or at least whatever aspect of procfs that 
we are relying on in this function).

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org