[RFC] don't create cpu/online sysfs file

[Joel Schopp]

I might change cpu_is_hotpluggable to __cpu_is_hotpluggable to help
indicate it is a platform specific function.  Also, won't you want to
stub out the function for the other platforms that do cpu hotplug?

-Joel

Dave Hansen wrote:

> I sent this out earlier this week, but wanted to make sure everybody is
> happy with it before I sent it upstream.  I'm doing it backwards:
> [PATCH] before [RFC]. :)
>
> Rusty said he didn't have a problem with it already.  Anton, do mind
> putting this in your patch queue, or should I send it upstream myself?
>
> --
>
> The following patch restricts creation of the
> /sys/devices/system/cpu/cpuX/online file to conditions where it is known
> that cpu hotplugging might be possible.  It also leaves room for a much
> more complex method of deciding this information in the future, on a
> per-cpu basis.
>
> It fixes a bug where CPU hotplug ppc64 RTAS calls were being made on a
> non-partitioned system.  This caused RTAS assertions, which are bad.
>
> Any new architecture that defines CONFIG_HOTPLUG_CPU will need to
> implement a cpu_is_hotpluggable() function.  This could be overcome by a
> series of #ifdefs, but I think someone porting CPU hotplug to a new
> architecture can figure this one out.
>                                                                                                                    Tested on 16-way ppc64 LPAR and 8-way bare-metal ppc64.  Compile tested
> on x86.
>
> -- Dave
>
>
> ------------------------------------------------------------------------
>
> Signed-off-by: Dave Hansen <haveblue at us.ibm.com>
>
> diff -urp linux-2.6.7-rc2-mm2-clean/arch/ppc64/kernel/smp.c linux-2.6.7-rc2-mm2-cpuonline/arch/ppc64/kernel/smp.c
> --- linux-2.6.7-rc2-mm2-clean/arch/ppc64/kernel/smp.c	Fri Jun  4 13:27:13 2004
> +++ linux-2.6.7-rc2-mm2-cpuonline/arch/ppc64/kernel/smp.c	Fri Jun  4 13:27:29 2004
> @@ -444,6 +444,21 @@ static inline void look_for_more_cpus(vo
>  	for (i = 0; i < maxcpus; i++)
>  		cpu_set(i, cpu_possible_map);
>  }
> +
> +int cpu_is_hotpluggable(struct cpu *cpu)
> +{
> +	/*
> +	 * For now, we just see if the system supports making
> +	 * the RTAS calls for CPU hotplug.  But, there may be a
> +	 * more comprehensive way to do this for an individual
> +	 * CPU.  For instance, the boot cpu might never be valid
> +	 * for hotplugging.
> +	 */
> +	if (systemcfg->platform == PLATFORM_PSERIES_LPAR)
> +		return 1;
> +
> +	return 0;
> +}
>  #else /* ... CONFIG_HOTPLUG_CPU */
>  static inline int __devinit smp_startup_cpu(unsigned int lcpu)
>  {
> diff -urp linux-2.6.7-rc2-mm2-clean/drivers/base/cpu.c linux-2.6.7-rc2-mm2-cpuonline/drivers/base/cpu.c
> --- linux-2.6.7-rc2-mm2-clean/drivers/base/cpu.c	Fri Jun  4 13:27:09 2004
> +++ linux-2.6.7-rc2-mm2-cpuonline/drivers/base/cpu.c	Fri Jun  4 13:27:29 2004
> @@ -48,7 +48,8 @@ static SYSDEV_ATTR(online, 0600, show_on
>
>  static void __init register_cpu_control(struct cpu *cpu)
>  {
> -	sysdev_create_file(&cpu->sysdev, &attr_online);
> +	if (cpu_is_hotpluggable(cpu))
> +		sysdev_create_file(&cpu->sysdev, &attr_online);
>  }
>  #else /* ... !CONFIG_HOTPLUG_CPU */
>  static inline void register_cpu_control(struct cpu *cpu)
> diff -urp linux-2.6.7-rc2-mm2-clean/include/linux/cpu.h linux-2.6.7-rc2-mm2-cpuonline/include/linux/cpu.h
> --- linux-2.6.7-rc2-mm2-clean/include/linux/cpu.h	Fri Jun  4 13:27:11 2004
> +++ linux-2.6.7-rc2-mm2-cpuonline/include/linux/cpu.h	Fri Jun  4 13:27:29 2004
> @@ -65,6 +65,10 @@ extern struct semaphore cpucontrol;
>  	register_cpu_notifier(&fn##_nb);			\
>  }
>  int cpu_down(unsigned int cpu);
> +
> +/* expected to be defined in arch-specific code */
> +extern int cpu_is_hotpluggable(struct cpu *cpu);
> +
>  #define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
>  #else
>  #define lock_cpu_hotplug()	do { } while (0)
> @@ -74,6 +78,7 @@ int cpu_down(unsigned int cpu);
>
>  /* CPUs don't go offline once they're online w/o CONFIG_HOTPLUG_CPU */
>  #define cpu_is_offline(cpu) 0
> +#define cpu_is_hotpluggable(cpu) 0
>  #endif
>
>  #endif /* _LINUX_CPU_H_ */

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