Re: [PATCH] sched_attr: Do not define for glibc >= 2.41

[Crystal Wood <crwood@redhat.com>]

On Wed, 2025-01-29 at 16:54 -0500, John Kacur wrote:
> 
> On Tue, 28 Jan 2025, Khem Raj wrote:
> 
> > glibc 2.41+ has added [1] definitions for sched_setattr and sched_getattr functions
> > and struct sched_attr. Therefore, it needs to be checked for here as well before
> > defining sched_attr
> > 
> > Define sched_attr conditionally on SCHED_ATTR_SIZE_VER0
> > 
> > Fixes builds with glibc/trunk
> > 
> > [1] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=21571ca0d70302909cf72707b2a7736cf12190a0;hp=298bc488fdc047da37482f4003023cb9adef78f8
> > 
> > Signed-off-by: Khem Raj <raj.khem@gmail.com>
> > Cc: Clark Williams <williams@redhat.com>
> > Cc: John Kacur <jkacur@redhat.com>
> > Cc: rt-users <linux-rt-users@vger.kernel.org>
> > ---
> >  src/include/rt-sched.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/src/include/rt-sched.h b/src/include/rt-sched.h
> > index 80171c7..9cf0e3a 100644
> > --- a/src/include/rt-sched.h
> > +++ b/src/include/rt-sched.h
> > @@ -42,6 +42,8 @@
> >  #define __NR_sched_getattr		275
> >  #endif
> >  
> > +/* sched_attr is not defined in glibc < 2.41 */
> > +#ifndef SCHED_ATTR_SIZE_VER0
> >  struct sched_attr {
> >  	uint32_t size;
> >  	uint32_t sched_policy;
> > @@ -68,4 +70,6 @@ int sched_getattr(pid_t pid,
> >  		  unsigned int size,
> >  		  unsigned int flags);
> >  
> > +#endif /* SCHED_ATTR_SIZE_VER0 */
> > +
> >  #endif /* __RT_SCHED_H__ */
> > 
> > 
> 
> Does the following fix your problem?
[snip]

> +#if ! __GLIBC_PREREQ(2, 41)

I'm not familiar with the norms surrounding use of this macro, but it's
generally better to test features than versions... what if this feature
gets backported into some distro's earlier-version-numbered glibc?

FWIW, it looks like QEMU went with the feature test approach:
https://patchwork.ozlabs.org/project/qemu-devel/patch/20241011054806.1014276-1-raj.khem@gmail.com/
https://patchwork.ozlabs.org/project/qemu-devel/patch/20241011193140.1047648-1-raj.khem@gmail.com/

Also, was that patch posted anywhere?  Just wondering if I've still got
problems with email filtering.

-Crystal