extlinux/mountinfo.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2012 Intel Corporation; All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
   8  *   Boston MA 02110-1301, USA; either version 2 of the License, or
   9  *   (at your option) any later version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 #include <stdio.h>
  14 #include <string.h>
  15 #include <limits.h>
  16 #include <stdlib.h>
  17 #include <errno.h>
  18 #include <unistd.h>
  19 #include <sys/stat.h>
  20 #include <sys/sysmacros.h>
  21 #include "mountinfo.h"
  22
  23 /*
  24  * Parse /proc/self/mountinfo
  25  */
  26 static int get_string(FILE *f, char *string_buf, size_t string_len, char *ec)
  27 {
  28     int ch;
  29     char *p = string_buf;
  30
  31     for (;;) {
  32         if (!string_len)
  33             return -2;          /* String too long */
  34
  35         ch = getc(f);
  36         if (ch == EOF) {
  37             return -1;          /* Got EOF */
  38         } else if (ch == ' ' || ch == '\t' || ch == '\n') {
  39             *ec = ch;
  40             *p = '\0';
  41             return p - string_buf;
  42         } else if (ch == '\\') {
  43             /* Should always be followed by 3 octal digits in 000..377 */
  44             int oc = 0;
  45             int i;
  46             for (i = 0; i < 3; i++) {
  47                 ch = getc(f);
  48                 if (ch < '0' || ch > '7' || (i == 0 && ch > '3'))
  49                     return -1;  /* Bad escape sequence */
  50                 oc = (oc << 3) + (ch - '0');
  51             }
  52             if (!oc)
  53                 return -1;      /* We can't handle \000 */
  54             *p++ = oc;
  55             string_len--;
  56         } else {
  57             *p++ = ch;
  58             string_len--;
  59         }
  60     }
  61 }
  62
  63 static void free_mountinfo(struct mountinfo *m)
  64 {
  65     struct mountinfo *nx;
  66
  67     while (m) {
  68         free((char *)m->root);
  69         free((char *)m->path);
  70         free((char *)m->fstype);
  71         free((char *)m->devpath);
  72         free((char *)m->mountopt);
  73         nx = m->next;
  74         free(m);
  75         m = nx;
  76     }
  77 }
  78
  79 static struct mountinfo *head = NULL, **tail = &head;
  80
  81 static void parse_mountinfo(void)
  82 {
  83     FILE *f;
  84     struct mountinfo *m, *mm;
  85     char string_buf[PATH_MAX*8];
  86     int n;
  87     char ec, *ep;
  88     unsigned int ma, mi;
  89
  90     f = fopen("/proc/self/mountinfo", "r");
  91     if (!f)
  92         return;
  93
  94     for (;;) {
  95         m = malloc(sizeof(struct mountinfo));
  96         if (!m)
  97             break;
  98         memset(m, 0, sizeof *m);
  99
 100         n = get_string(f, string_buf, sizeof string_buf, &ec);
 101         if (n < 0 || ec == '\n')
 102             break;
 103
 104         m->mountid = strtoul(string_buf, &ep, 10);
 105         if (*ep)
 106             break;
 107
 108         n = get_string(f, string_buf, sizeof string_buf, &ec);
 109         if (n < 0 || ec == '\n')
 110             break;
 111
 112         m->parentid = strtoul(string_buf, &ep, 10);
 113         if (*ep)
 114             break;
 115
 116         n = get_string(f, string_buf, sizeof string_buf, &ec);
 117         if (n < 0 || ec == '\n')
 118             break;
 119
 120         if (sscanf(string_buf, "%u:%u", &ma, &mi) != 2)
 121             break;
 122
 123         m->dev = makedev(ma, mi);
 124
 125         n = get_string(f, string_buf, sizeof string_buf, &ec);
 126         if (n < 1 || ec == '\n' || string_buf[0] != '/')
 127             break;
 128
 129         m->root = strdup(string_buf);
 130         if (!m->root)
 131             break;
 132
 133         n = get_string(f, string_buf, sizeof string_buf, &ec);
 134         if (n < 1 || ec == '\n' || string_buf[0] != '/')
 135             break;
 136
 137         m->path = strdup(string_buf);
 138         m->pathlen = (n == 1) ? 0 : n; /* Treat / as empty */
 139
 140         /* Skip tagged attributes */
 141         do {
 142             n = get_string(f, string_buf, sizeof string_buf, &ec);
 143             if (n < 0 || ec == '\n')
 144                 goto quit;
 145         } while (n != 1 || string_buf[0] != '-');
 146
 147         n = get_string(f, string_buf, sizeof string_buf, &ec);
 148         if (n < 0 || ec == '\n')
 149             break;
 150
 151         m->fstype = strdup(string_buf);
 152         if (!m->fstype)
 153             break;
 154
 155         n = get_string(f, string_buf, sizeof string_buf, &ec);
 156         if (n < 0 || ec == '\n')
 157             break;
 158
 159         m->devpath = strdup(string_buf);
 160         if (!m->devpath)
 161             break;
 162
 163         n = get_string(f, string_buf, sizeof string_buf, &ec);
 164         if (n < 0)
 165             break;
 166
 167         m->mountopt = strdup(string_buf);
 168         if (!m->mountopt)
 169             break;
 170
 171         /* Skip any previously unknown fields */
 172         while (ec != '\n' && ec != EOF)
 173             ec = getc(f);
 174
 175         *tail = m;
 176         tail = &m->next;
 177     }
 178 quit:
 179     fclose(f);
 180     free_mountinfo(m);
 181
 182     /* Create parent links */
 183     for (m = head; m; m = m->next) {
 184         for (mm = head; mm; mm = mm->next) {
 185             if (m->parentid == mm->mountid) {
 186                 m->parent = mm;
 187                 if (!strcmp(m->path, mm->path))
 188                     mm->hidden = 1; /* Hidden under another mount */
 189                 break;
 190             }
 191         }
 192     }
 193 }
 194
 195 const struct mountinfo *find_mount(const char *path, char **subpath)
 196 {
 197     static int done_init;
 198     char *real_path;
 199     const struct mountinfo *m, *best;
 200     struct stat st;
 201     int len, matchlen;
 202
 203     if (!done_init) {
 204         parse_mountinfo();
 205         done_init = 1;
 206     }
 207
 208     if (stat(path, &st))
 209         return NULL;
 210
 211     real_path = realpath(path, NULL);
 212     if (!real_path)
 213         return NULL;
 214
 215     /*
 216      * Tricky business: we need the longest matching subpath
 217      * which isn't a parent of the same subpath.
 218      */
 219     len = strlen(real_path);
 220     matchlen = 0;
 221     best = NULL;
 222     for (m = head; m; m = m->next) {
 223         if (m->hidden)
 224             continue;           /* Hidden underneath another mount */
 225
 226         if (m->pathlen > len)
 227             continue;           /* Cannot possibly match */
 228
 229         if (m->pathlen < matchlen)
 230             continue;           /* No point in testing this one */
 231
 232         if (st.st_dev == m->dev &&
 233             !memcmp(m->path, real_path, m->pathlen) &&
 234             (real_path[m->pathlen] == '/' || real_path[m->pathlen] == '\0')) {
 235             matchlen = m->pathlen;
 236             best = m;
 237         }
 238     }
 239
 240     if (best && subpath) {
 241         if (real_path[best->pathlen] == '\0')
 242             *subpath = strdup("/");
 243         else
 244             *subpath = strdup(real_path + best->pathlen);
 245     }
 246
 247     return best;
 248 }
 249
 250 #ifdef TEST
 251
 252 int main(int argc, char *argv[])
 253 {
 254     int i;
 255     const struct mountinfo *m;
 256     char *subpath;
 257
 258     parse_mountinfo();
 259
 260     for (i = 1; i < argc; i++) {
 261         m = find_mount(argv[i], &subpath);
 262         if (!m) {
 263             printf("%s: %s\n", argv[i], strerror(errno));
 264             continue;
 265         }
 266
 267         printf("%s -> %s @ %s(%u,%u):%s %s %s\n",
 268                argv[i], subpath, m->devpath, major(m->dev), minor(m->dev),
 269                m->root, m->fstype, m->mountopt);
 270         printf("Usable device: %s\n", find_device(m->dev, m->devpath));
 271         free(subpath);
 272     }
 273
 274     return 0;
 275 }
 276
 277 #endif