Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ] 
  1 /*
  2  * Copyright 2006 Andi Kleen, SUSE Labs.
  3  * Subject to the GNU Public License, v.2
  4  *
  5  * Fast user context implementation of clock_gettime and gettimeofday.
  6  *
  7  * The code should have no internal unresolved relocations.
  8  * Check with readelf after changing.
  9  * Also alternative() doesn't work.
 10  */
 11 
 12 /* Disable profiling for userspace code: */
 13 #define DISABLE_BRANCH_PROFILING
 14 
 15 #include <linux/kernel.h>
 16 #include <linux/posix-timers.h>
 17 #include <linux/time.h>
 18 #include <linux/string.h>
 19 #include <asm/vsyscall.h>
 20 #include <asm/vgtod.h>
 21 #include <asm/timex.h>
 22 #include <asm/hpet.h>
 23 #include <asm/unistd.h>
 24 #include <asm/io.h>
 25 #include "vextern.h"
 26 
 27 #define gtod vdso_vsyscall_gtod_data
 28 
 29 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 30 {
 31         long ret;
 32         asm("syscall" : "=a" (ret) :
 33             "" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
 34         return ret;
 35 }
 36 
 37 notrace static inline long vgetns(void)
 38 {
 39         long v;
 40         cycles_t (*vread)(void);
 41         vread = gtod->clock.vread;
 42         v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
 43         return (v * gtod->clock.mult) >> gtod->clock.shift;
 44 }
 45 
 46 notrace static noinline int do_realtime(struct timespec *ts)
 47 {
 48         unsigned long seq, ns;
 49         do {
 50                 seq = read_seqbegin(&gtod->lock);
 51                 ts->tv_sec = gtod->wall_time_sec;
 52                 ts->tv_nsec = gtod->wall_time_nsec;
 53                 ns = vgetns();
 54         } while (unlikely(read_seqretry(&gtod->lock, seq)));
 55         timespec_add_ns(ts, ns);
 56         return 0;
 57 }
 58 
 59 /* Copy of the version in kernel/time.c which we cannot directly access */
 60 notrace static void
 61 vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
 62 {
 63         while (nsec >= NSEC_PER_SEC) {
 64                 nsec -= NSEC_PER_SEC;
 65                 ++sec;
 66         }
 67         while (nsec < 0) {
 68                 nsec += NSEC_PER_SEC;
 69                 --sec;
 70         }
 71         ts->tv_sec = sec;
 72         ts->tv_nsec = nsec;
 73 }
 74 
 75 notrace static noinline int do_monotonic(struct timespec *ts)
 76 {
 77         unsigned long seq, ns, secs;
 78         do {
 79                 seq = read_seqbegin(&gtod->lock);
 80                 secs = gtod->wall_time_sec;
 81                 ns = gtod->wall_time_nsec + vgetns();
 82                 secs += gtod->wall_to_monotonic.tv_sec;
 83                 ns += gtod->wall_to_monotonic.tv_nsec;
 84         } while (unlikely(read_seqretry(&gtod->lock, seq)));
 85         vset_normalized_timespec(ts, secs, ns);
 86         return 0;
 87 }
 88 
 89 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
 90 {
 91         if (likely(gtod->sysctl_enabled && gtod->clock.vread))
 92                 switch (clock) {
 93                 case CLOCK_REALTIME:
 94                         return do_realtime(ts);
 95                 case CLOCK_MONOTONIC:
 96                         return do_monotonic(ts);
 97                 }
 98         return vdso_fallback_gettime(clock, ts);
 99 }
100 int clock_gettime(clockid_t, struct timespec *)
101         __attribute__((weak, alias("__vdso_clock_gettime")));
102 
103 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
104 {
105         long ret;
106         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
107                 if (likely(tv != NULL)) {
108                         BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
109                                      offsetof(struct timespec, tv_nsec) ||
110                                      sizeof(*tv) != sizeof(struct timespec));
111                         do_realtime((struct timespec *)tv);
112                         tv->tv_usec /= 1000;
113                 }
114                 if (unlikely(tz != NULL)) {
115                         /* Avoid memcpy. Some old compilers fail to inline it */
116                         tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
117                         tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
118                 }
119                 return 0;
120         }
121         asm("syscall" : "=a" (ret) :
122             "" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
123         return ret;
124 }
125 int gettimeofday(struct timeval *, struct timezone *)
126         __attribute__((weak, alias("__vdso_gettimeofday")));
127
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