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