Re: [Qemu-devel] [PATCH] qemu-ga: guest-shutdown: use only async-signal-safe functions

[Eric Blake <eblake@redhat.com>]

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On 05/14/2012 12:03 PM, Luiz Capitulino wrote:
> On Mon, 14 May 2012 15:01:17 -0300
> Luiz Capitulino <lcapitulino@redhat.com> wrote:
> 
>>>> +
>>>> +        ret = execle("/sbin/shutdown", "shutdown", shutdown_flag, "+0",
>>>> +                    "hypervisor initiated shutdown", (char*)NULL, environ);
>>>
>>> Where was 'environ' declared?  POSIX says that environ must exist, but
>>> that it is the one variable where you must declare it yourself rather
>>> than getting it from a public header.  (For convenience, glibc declares
>>> environ in <unistd.h> when using _GNU_SOURCE, but when you are asking
>>> for strict standards namespace compliance, it disappears.)
>>
>> I'll declare it then.
> 
> -Wredundant-decls doesn't like it:
> 
> /home/lcapitulino/work/src/qmp-unstable/qga/commands-posix.c:38:15: warning: redundant redeclaration of ‘environ’ [-Wredundant-decls]
> /usr/include/unistd.h:546:15: note: previous declaration of ‘environ’ was here
>   LINK  qemu-ga

Hmm, gnulib works around that by probing for whether environ was
declared at configure time, in order to conditionalize whether to output
a declaration of its own; but obviously we aren't using gnulib.  Maybe,
since we know that the glibc declaration is guarded by _GNU_SOURCE, we
could likewise guard our declaration to only occur in the situations
where glibc is not declaring it?  Or maybe we can factor things into a
common header used by other qemu files, where the header file itself is
tagged in such a way to silence gcc warnings about any possible
duplicate declaration, while still leaving the .c files that use this
common header clean for use of -Wredundant-decls?

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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