root/arch/x86/include/asm/vgtod.h

DEFINITIONS

1. gtod_read_begin
2. gtod_read_retry
3. gtod_write_begin
4. gtod_write_end

#ifndef _ASM_X86_VGTOD_H
#define _ASM_X86_VGTOD_H

#include <linux/compiler.h>
#include <linux/clocksource.h>

#ifdef BUILD_VDSO32_64
typedef u64 gtod_long_t;
#else
typedef unsigned long gtod_long_t;
#endif
/*
 * vsyscall_gtod_data will be accessed by 32 and 64 bit code at the same time
 * so be carefull by modifying this structure.
 */
struct vsyscall_gtod_data {
        unsigned seq;

        int vclock_mode;
        cycle_t cycle_last;
        cycle_t mask;
        u32     mult;
        u32     shift;

        /* open coded 'struct timespec' */
        u64             wall_time_snsec;
        gtod_long_t     wall_time_sec;
        gtod_long_t     monotonic_time_sec;
        u64             monotonic_time_snsec;
        gtod_long_t     wall_time_coarse_sec;
        gtod_long_t     wall_time_coarse_nsec;
        gtod_long_t     monotonic_time_coarse_sec;
        gtod_long_t     monotonic_time_coarse_nsec;

        int             tz_minuteswest;
        int             tz_dsttime;
};
extern struct vsyscall_gtod_data vsyscall_gtod_data;

static inline unsigned gtod_read_begin(const struct vsyscall_gtod_data *s)
{
        unsigned ret;

repeat:
        ret = ACCESS_ONCE(s->seq);
        if (unlikely(ret & 1)) {
                cpu_relax();
                goto repeat;
        }
        smp_rmb();
        return ret;
}

static inline int gtod_read_retry(const struct vsyscall_gtod_data *s,
                                        unsigned start)
{
        smp_rmb();
        return unlikely(s->seq != start);
}

static inline void gtod_write_begin(struct vsyscall_gtod_data *s)
{
        ++s->seq;
        smp_wmb();
}

static inline void gtod_write_end(struct vsyscall_gtod_data *s)
{
        smp_wmb();
        ++s->seq;
}

#endif /* _ASM_X86_VGTOD_H */