Help: Using cpufreq from kernel level

[Claudio Scordino <cloud.of.andor@gmail.com>]

Hi all,

   I'm writing a kernel module that needs to get info about the available 
frequencies on the current processor and to periodically change the current 
frequency.

At user level it can be done through

/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

but I have no idea how to implement it at kernel level. 

I tried to declare

extern struct cpufreq_driver    *cpufreq_driver;
extern struct cpufreq_policy    *cpufreq_cpu_data[NR_CPUS];
extern spinlock_t cpufreq_driver_lock;
extern ssize_t show_available_freqs (struct cpufreq_policy *policy, char 
*buf);

and to do

char buffer [100000] = "\n";
spin_lock_irqsave(&cpufreq_driver_lock, flags);
show_available_freqs(cpufreq_cpu_data[0], buffer);
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

but it crashes the system.

Please, can somebody tell me how this can be done ?

Many thanks,

        Claudio Scordino