How do I include Linux header files like linux/getcpu.h?

I'm using Linux 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:31:23 UTC 2012 x86_64 GNU/Linux, and I need to #include<linux/getcpu.h>. The compiler complains that it cannot find the file. Where are the header files for linux?

Solution

Short answer: usually, you don't include those headers directly.

Most OS/Machine specific headers in there are automatically included for you by a more general header. Those that are not are linux only features which may or may not be available for the version you are running.

As to getcpu, there is a more standardised version called sched_getcpu which is found in sched.h and has the same function.

Alternatively you can test wether that system call is available on your system and call it manually:

#define _GNU_SOURCE  
#include <unistd.h>
#include <sys/syscall.h>

static inline int getcpu() {
    #ifdef SYS_getcpu
    int cpu, status;
    status = syscall(SYS_getcpu, &cpu, NULL, NULL);
    return (status == -1) ? status : cpu;
    #else
    return -1; // unavailable
    #endif
}

The variable errno (#include <errno.h>) gives the error code, if syscall returns -1.