Re: [Qemu-devel] [PATCH] qemu-timer: Check for usable fields for SIGEV_THREAD_ID

[Aurelien Jarno <aurelien@aurel32.net>]

On Fri, Oct 12, 2012 at 09:26:55AM -0700, Richard Henderson wrote:
> Older glibc (RHEL 5.x, Debian 5.x) does not have the _sigev_un._tid
> member in its structure definition, while the accompanying kernel
> headers do define SIGEV_THREAD_ID.  We need configure to check for
> both before using it.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Anthony Liguori <aliguori@us.ibm.com>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  configure    | 21 +++++++++++++++++++++
>  qemu-timer.c |  4 ++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
> 
> FWIW, RHEL 5 is the last release for ia64.  And for whatever reason,
> the ultrasparc in the gcc compile farm is still running Lenny.  I've
> been hacking around this for some time, and now finally got around to
> submitting a proper patch for it.
> 
> 
> r~
> 
> 
> diff --git a/configure b/configure
> index c4a7837..78d8819 100755
> --- a/configure
> +++ b/configure
> @@ -2841,6 +2841,23 @@ if compile_prog "" "" ; then
>  fi
>  
>  ##########################################
> +# check if we have usable SIGEV_THREAD_ID
> +
> +sigev_thread_id=no
> +cat > $TMPC << EOF
> +#include <signal.h>
> +int main(void) {
> +  struct sigevent ev;
> +  ev.sigev_notify = SIGEV_THREAD_ID;
> +  ev._sigev_un._tid = 0;
> +  return 0;
> +}
> +EOF
> +if compile_prog "" "" ; then
> +    sigev_thread_id=yes
> +fi
> +
> +##########################################
>  # check if trace backend exists
>  
>  $python "$source_path/scripts/tracetool.py" "--backend=$trace_backend" --check-backend  > /dev/null 2> /dev/null
> @@ -3186,6 +3203,7 @@ echo "preadv support    $preadv"
>  echo "fdatasync         $fdatasync"
>  echo "madvise           $madvise"
>  echo "posix_madvise     $posix_madvise"
> +echo "sigev_thread_id   $sigev_thread_id"
>  echo "uuid support      $uuid"
>  echo "libcap-ng support $cap_ng"
>  echo "vhost-net support $vhost_net"
> @@ -3469,6 +3487,9 @@ fi
>  if test "$posix_madvise" = "yes" ; then
>    echo "CONFIG_POSIX_MADVISE=y" >> $config_host_mak
>  fi
> +if test "$sigev_thread_id" = "yes" ; then
> +  echo "CONFIG_SIGEV_THREAD_ID=y" >> $config_host_mak
> +fi
>  
>  if test "$spice" = "yes" ; then
>    echo "CONFIG_SPICE=y" >> $config_host_mak
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 908a103..ede84ff 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -494,12 +494,12 @@ static int dynticks_start_timer(struct qemu_alarm_timer *t)
>      memset(&ev, 0, sizeof(ev));
>      ev.sigev_value.sival_int = 0;
>      ev.sigev_notify = SIGEV_SIGNAL;
> -#ifdef SIGEV_THREAD_ID
> +#ifdef CONFIG_SIGEV_THREAD_ID
>      if (qemu_signalfd_available()) {
>          ev.sigev_notify = SIGEV_THREAD_ID;
>          ev._sigev_un._tid = qemu_get_thread_id();
>      }
> -#endif /* SIGEV_THREAD_ID */
> +#endif /* CONFIG_SIGEV_THREAD_ID */
>      ev.sigev_signo = SIGALRM;
>  
>      if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {

Looks good on principle, but doesn't work for me. Running configure I
get:

| $./configure 
| ERROR: configure test passed without -Werror but failed with -Werror.
| This is probably a bug in the configure script. The failing command
| will be at the bottom of config.log.
| You can run configure with --disable-werror to bypass this check.
| $

And config.log contains:

| /tmp/qemu-conf--6963-.c: In function ‘main’:
| /tmp/qemu-conf--6963-.c:3:19: error: variable ‘ev’ set but not used [-Werror=unused-but-set-variable]
| cc1: all warnings being treated as errors

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net