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Re: [Qemu-devel] [PATCH] main_loop: Make main_loop_wait() return void

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] main_loop: Make main_loop_wait() return void
Date: Fri, 31 Mar 2017 09:10:03 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 03/31/2017 08:51 AM, Peter Maydell wrote:
> In commit e330c118f2a5a the last usage of main_loop_wait() that cared
> about the return value was changed to no longer use it. Drop the
> now-useless return value and make the function return void.
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> Coverity complains (CID 1372464) about main_loop() calling
> main_loop_wait() and ignoring its return value. I suspect
> this change will just displace that to within main_loop_wait()
> itself since the underlying issue there is "the ppoll() that
> gets called to poll fds can return an error code, but what
> do we do if it does?". Suggestions on that point welcome.

At one point, there was a suggestion to introduce an ignore_value()
macro that ignores values that the compiler/coverity would otherwise
complain about, in contexts where we really are okay ignoring the value.
 If making main_loop_wait() return void shifts where Coverity blames,
then ignore_value(ppoll()) seems like it might help.

> I guess this will make the compiler warn about ret being
> set and never used if CONFIG_SLIRP is not defined, which
> is irritating. I'm postponing messing about with fixing
> that in favour of seeing whether anybody has a good answer
> to the question above (which might make it moot).
> ---

> -int main_loop_wait(int nonblocking)
> +void main_loop_wait(int nonblocking)
>  {
>      int ret;
>      uint32_t timeout = UINT32_MAX;
> @@ -513,7 +513,7 @@ int main_loop_wait(int nonblocking)
>      qemu_start_warp_timer();
>      qemu_clock_run_all_timers();
> -    return ret;
> +    return;
>  }

We generally avoid lone return; at the end of a void function.

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

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