tools/lib/api/fs/tracefs.c

   1 #include <errno.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>
   5 #include <unistd.h>
   6 #include <stdbool.h>
   7 #include <sys/vfs.h>
   8 #include <sys/types.h>
   9 #include <sys/stat.h>
  10 #include <sys/mount.h>
  11 #include <linux/kernel.h>
  12
  13 #include "tracefs.h"
  14
  15 #ifndef TRACEFS_DEFAULT_PATH
  16 #define TRACEFS_DEFAULT_PATH            "/sys/kernel/tracing"
  17 #endif
  18
  19 char tracefs_mountpoint[PATH_MAX + 1] = TRACEFS_DEFAULT_PATH;
  20
  21 static const char * const tracefs_known_mountpoints[] = {
  22         TRACEFS_DEFAULT_PATH,
  23         "/sys/kernel/debug/tracing",
  24         "/tracing",
  25         "/trace",
  26         0,
  27 };
  28
  29 static bool tracefs_found;
  30
  31 bool tracefs_configured(void)
  32 {
  33         return tracefs_find_mountpoint() != NULL;
  34 }
  35
  36 /* find the path to the mounted tracefs */
  37 const char *tracefs_find_mountpoint(void)
  38 {
  39         const char *ret;
  40
  41         if (tracefs_found)
  42                 return (const char *)tracefs_mountpoint;
  43
  44         ret = find_mountpoint("tracefs", (long) TRACEFS_MAGIC,
  45                               tracefs_mountpoint, PATH_MAX + 1,
  46                               tracefs_known_mountpoints);
  47
  48         if (ret)
  49                 tracefs_found = true;
  50
  51         return ret;
  52 }
  53
  54 /* mount the tracefs somewhere if it's not mounted */
  55 char *tracefs_mount(const char *mountpoint)
  56 {
  57         /* see if it's already mounted */
  58         if (tracefs_find_mountpoint())
  59                 goto out;
  60
  61         /* if not mounted and no argument */
  62         if (mountpoint == NULL) {
  63                 /* see if environment variable set */
  64                 mountpoint = getenv(PERF_TRACEFS_ENVIRONMENT);
  65                 /* if no environment variable, use default */
  66                 if (mountpoint == NULL)
  67                         mountpoint = TRACEFS_DEFAULT_PATH;
  68         }
  69
  70         if (mount(NULL, mountpoint, "tracefs", 0, NULL) < 0)
  71                 return NULL;
  72
  73         /* save the mountpoint */
  74         tracefs_found = true;
  75         strncpy(tracefs_mountpoint, mountpoint, sizeof(tracefs_mountpoint));
  76 out:
  77         return tracefs_mountpoint;
  78 }