Re: [Qemu-devel] [PATCH] Add configure clock_gettime() monotonic time test

[Anthony Liguori <anthony@codemonkey.ws>]

Brad Smith <brad@comstyle.com> writes:

> On Wed, Apr 03, 2013 at 03:22:24PM -0400, Brad Smith wrote:
>> On Wed, Apr 03, 2013 at 10:18:51AM +0200, Paolo Bonzini wrote:
>> > Il 03/04/2013 00:52, Peter Maydell ha scritto:
>> > > On 2 April 2013 17:45, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> > >> Il 02/04/2013 17:42, Brad Smith ha scritto:
>> > >>> Replace the hardcoded list of OS's utilizing clock_gettime() for monotonic
>> > >>> time with a configure test. This is to fix the use of monotonic time on
>> > >>> OpenBSD but allows for other POSIX compliant OS's such as NetBSD to also
>> > >>> utilize clock_gettime().
>> > >>
>> > >> I thought the list of OSes was supposed to filter out those that somehow
>> > >> had a broken CLOCK_MONOTONIC.
>> > > 
>> > > Judging from wading through git history, it's mostly just
>> > > historic accretion from an initial #ifdef __linux__ which was
>> > > put in by Fabrice way back when configure was barely doing
>> > > compile-this-code checks at all.
>> > > 
>> > > Google does suggest that some OSes do provide a CLOCK_MONOTONIC
>> > > but clock_gettime(CLOCK_MONOTONIC) always fails, eg Centos 3.
>> > 
>> > It would already fail, and no one reported it.
>> > 
>> > CentOS 3 has a 2.4 kernel.  I doubt anyone is using it with a recent QEMU.
>> > 
>> > Paolo
>> > 
>> > >> Otherwise, you might as well use "#ifdef CLOCK_MONOTONIC" and skip the
>> > >> configure test completely.
>> > > 
>> > > Tempting.
>> > > 
>> > > -- PMM
>> 
>> Then how about the following? This looks like it should be good
>> for Linux, *BSD's, Solaris.
>
> Any further comments?

Please submit a top-level patch and I'll apply it.

Regards,

Anthony Liguori

>
>> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
>> index 1766b2d..c363190 100644
>> --- a/include/qemu/timer.h
>> +++ b/include/qemu/timer.h
>> @@ -117,8 +117,7 @@ extern int use_rt_clock;
>>  
>>  static inline int64_t get_clock(void)
>>  {
>> -#if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 500000) \
>> -    || defined(__DragonFly__) || defined(__FreeBSD_kernel__)
>> +#ifdef CLOCK_MONOTONIC
>>      if (use_rt_clock) {
>>          struct timespec ts;
>>          clock_gettime(CLOCK_MONOTONIC, &ts);
>> diff --git a/util/qemu-timer-common.c b/util/qemu-timer-common.c
>> index 16f5e75..95e0847 100644
>> --- a/util/qemu-timer-common.c
>> +++ b/util/qemu-timer-common.c
>> @@ -49,9 +49,7 @@ int use_rt_clock;
>>  static void __attribute__((constructor)) init_get_clock(void)
>>  {
>>      use_rt_clock = 0;
>> -#if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 500000) \
>> -    || defined(__DragonFly__) || defined(__FreeBSD_kernel__) \
>> -    || defined(__OpenBSD__)
>> +#ifdef CLOCK_MONOTONIC
>>      {
>>          struct timespec ts;
>>          if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0) {
>> 
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>> 
>
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