tools/perf/util/cloexec.c

   1 #include <sched.h>
   2 #include "util.h"
   3 #include "../perf.h"
   4 #include "cloexec.h"
   5 #include "asm/bug.h"
   6 #include "debug.h"
   7 #include <unistd.h>
   8 #include <asm/unistd.h>
   9 #include <sys/syscall.h>
  10
  11 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
  12
  13 int __weak sched_getcpu(void)
  14 {
  15 #ifdef __NR_getcpu
  16         unsigned cpu;
  17         int err = syscall(__NR_getcpu, &cpu, NULL, NULL);
  18         if (!err)
  19                 return cpu;
  20 #else
  21         errno = ENOSYS;
  22 #endif
  23         return -1;
  24 }
  25
  26 static int perf_flag_probe(void)
  27 {
  28         /* use 'safest' configuration as used in perf_evsel__fallback() */
  29         struct perf_event_attr attr = {
  30                 .type = PERF_TYPE_SOFTWARE,
  31                 .config = PERF_COUNT_SW_CPU_CLOCK,
  32                 .exclude_kernel = 1,
  33         };
  34         int fd;
  35         int err;
  36         int cpu;
  37         pid_t pid = -1;
  38         char sbuf[STRERR_BUFSIZE];
  39
  40         cpu = sched_getcpu();
  41         if (cpu < 0)
  42                 cpu = 0;
  43
  44         /*
  45          * Using -1 for the pid is a workaround to avoid gratuitous jump label
  46          * changes.
  47          */
  48         while (1) {
  49                 /* check cloexec flag */
  50                 fd = sys_perf_event_open(&attr, pid, cpu, -1,
  51                                          PERF_FLAG_FD_CLOEXEC);
  52                 if (fd < 0 && pid == -1 && errno == EACCES) {
  53                         pid = 0;
  54                         continue;
  55                 }
  56                 break;
  57         }
  58         err = errno;
  59
  60         if (fd >= 0) {
  61                 close(fd);
  62                 return 1;
  63         }
  64
  65         WARN_ONCE(err != EINVAL && err != EBUSY,
  66                   "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
  67                   err, str_error_r(err, sbuf, sizeof(sbuf)));
  68
  69         /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
  70         while (1) {
  71                 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
  72                 if (fd < 0 && pid == -1 && errno == EACCES) {
  73                         pid = 0;
  74                         continue;
  75                 }
  76                 break;
  77         }
  78         err = errno;
  79
  80         if (fd >= 0)
  81                 close(fd);
  82
  83         if (WARN_ONCE(fd < 0 && err != EBUSY,
  84                       "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
  85                       err, str_error_r(err, sbuf, sizeof(sbuf))))
  86                 return -1;
  87
  88         return 0;
  89 }
  90
  91 unsigned long perf_event_open_cloexec_flag(void)
  92 {
  93         static bool probed;
  94
  95         if (!probed) {
  96                 if (perf_flag_probe() <= 0)
  97                         flag = 0;
  98                 probed = true;
  99         }
 100
 101         return flag;
 102 }