tools/lib/api/fs/debugfs.c

   1 #define _GNU_SOURCE
   2 #include <errno.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include <string.h>
   6 #include <stdbool.h>
   7 #include <sys/vfs.h>
   8 #include <sys/mount.h>
   9 #include <linux/kernel.h>
  10
  11 #include "debugfs.h"
  12
  13 char debugfs_mountpoint[PATH_MAX + 1] = "/sys/kernel/debug";
  14
  15 static const char * const debugfs_known_mountpoints[] = {
  16         "/sys/kernel/debug",
  17         "/debug",
  18         0,
  19 };
  20
  21 static bool debugfs_found;
  22
  23 /* find the path to the mounted debugfs */
  24 const char *debugfs_find_mountpoint(void)
  25 {
  26         const char * const *ptr;
  27         char type[100];
  28         FILE *fp;
  29
  30         if (debugfs_found)
  31                 return (const char *)debugfs_mountpoint;
  32
  33         ptr = debugfs_known_mountpoints;
  34         while (*ptr) {
  35                 if (debugfs_valid_mountpoint(*ptr) == 0) {
  36                         debugfs_found = true;
  37                         strcpy(debugfs_mountpoint, *ptr);
  38                         return debugfs_mountpoint;
  39                 }
  40                 ptr++;
  41         }
  42
  43         /* give up and parse /proc/mounts */
  44         fp = fopen("/proc/mounts", "r");
  45         if (fp == NULL)
  46                 return NULL;
  47
  48         while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
  49                       debugfs_mountpoint, type) == 2) {
  50                 if (strcmp(type, "debugfs") == 0)
  51                         break;
  52         }
  53         fclose(fp);
  54
  55         if (strcmp(type, "debugfs") != 0)
  56                 return NULL;
  57
  58         debugfs_found = true;
  59
  60         return debugfs_mountpoint;
  61 }
  62
  63 /* verify that a mountpoint is actually a debugfs instance */
  64
  65 int debugfs_valid_mountpoint(const char *debugfs)
  66 {
  67         struct statfs st_fs;
  68
  69         if (statfs(debugfs, &st_fs) < 0)
  70                 return -ENOENT;
  71         else if ((long)st_fs.f_type != (long)DEBUGFS_MAGIC)
  72                 return -ENOENT;
  73
  74         return 0;
  75 }
  76
  77 /* mount the debugfs somewhere if it's not mounted */
  78 char *debugfs_mount(const char *mountpoint)
  79 {
  80         /* see if it's already mounted */
  81         if (debugfs_find_mountpoint())
  82                 goto out;
  83
  84         /* if not mounted and no argument */
  85         if (mountpoint == NULL) {
  86                 /* see if environment variable set */
  87                 mountpoint = getenv(PERF_DEBUGFS_ENVIRONMENT);
  88                 /* if no environment variable, use default */
  89                 if (mountpoint == NULL)
  90                         mountpoint = "/sys/kernel/debug";
  91         }
  92
  93         if (mount(NULL, mountpoint, "debugfs", 0, NULL) < 0)
  94                 return NULL;
  95
  96         /* save the mountpoint */
  97         debugfs_found = true;
  98         strncpy(debugfs_mountpoint, mountpoint, sizeof(debugfs_mountpoint));
  99 out:
 100         return debugfs_mountpoint;
 101 }
 102
 103 int debugfs__strerror_open(int err, char *buf, size_t size, const char *filename)
 104 {
 105         char sbuf[128];
 106
 107         switch (err) {
 108         case ENOENT:
 109                 if (debugfs_found) {
 110                         snprintf(buf, size,
 111                                  "Error:\tFile %s/%s not found.\n"
 112                                  "Hint:\tPerhaps this kernel misses some CONFIG_ setting to enable this feature?.\n",
 113                                  debugfs_mountpoint, filename);
 114                         break;
 115                 }
 116                 snprintf(buf, size, "%s",
 117                          "Error:\tUnable to find debugfs\n"
 118                          "Hint:\tWas your kernel compiled with debugfs support?\n"
 119                          "Hint:\tIs the debugfs filesystem mounted?\n"
 120                          "Hint:\tTry 'sudo mount -t debugfs nodev /sys/kernel/debug'");
 121                 break;
 122         case EACCES:
 123                 snprintf(buf, size,
 124                          "Error:\tNo permissions to read %s/%s\n"
 125                          "Hint:\tTry 'sudo mount -o remount,mode=755 %s'\n",
 126                          debugfs_mountpoint, filename, debugfs_mountpoint);
 127                 break;
 128         default:
 129                 snprintf(buf, size, "%s", strerror_r(err, sbuf, sizeof(sbuf)));
 130                 break;
 131         }
 132
 133         return 0;
 134 }
 135
 136 int debugfs__strerror_open_tp(int err, char *buf, size_t size, const char *sys, const char *name)
 137 {
 138         char path[PATH_MAX];
 139
 140         snprintf(path, PATH_MAX, "tracing/events/%s/%s", sys, name ?: "*");
 141
 142         return debugfs__strerror_open(err, buf, size, path);
 143 }