arch/um/os-Linux/umid.c

   1 /*
   2  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <dirent.h>
   9 #include <errno.h>
  10 #include <fcntl.h>
  11 #include <signal.h>
  12 #include <string.h>
  13 #include <unistd.h>
  14 #include <sys/stat.h>
  15 #include "init.h"
  16 #include "os.h"
  17
  18 #define UML_DIR "~/.uml/"
  19
  20 #define UMID_LEN 64
  21
  22 /* Changed by set_umid, which is run early in boot */
  23 static char umid[UMID_LEN] = { 0 };
  24
  25 /* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
  26 static char *uml_dir = UML_DIR;
  27
  28 static int __init make_uml_dir(void)
  29 {
  30         char dir[512] = { '\0' };
  31         int len, err;
  32
  33         if (*uml_dir == '~') {
  34                 char *home = getenv("HOME");
  35
  36                 err = -ENOENT;
  37                 if (home == NULL) {
  38                         printk(UM_KERN_ERR "make_uml_dir : no value in "
  39                                "environment for $HOME\n");
  40                         goto err;
  41                 }
  42                 strlcpy(dir, home, sizeof(dir));
  43                 uml_dir++;
  44         }
  45         strlcat(dir, uml_dir, sizeof(dir));
  46         len = strlen(dir);
  47         if (len > 0 && dir[len - 1] != '/')
  48                 strlcat(dir, "/", sizeof(dir));
  49
  50         err = -ENOMEM;
  51         uml_dir = malloc(strlen(dir) + 1);
  52         if (uml_dir == NULL) {
  53                 printf("make_uml_dir : malloc failed, errno = %d\n", errno);
  54                 goto err;
  55         }
  56         strcpy(uml_dir, dir);
  57
  58         if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
  59                 printf("Failed to mkdir '%s': %s\n", uml_dir, strerror(errno));
  60                 err = -errno;
  61                 goto err_free;
  62         }
  63         return 0;
  64
  65 err_free:
  66         free(uml_dir);
  67 err:
  68         uml_dir = NULL;
  69         return err;
  70 }
  71
  72 /*
  73  * Unlinks the files contained in @dir and then removes @dir.
  74  * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
  75  * ignore ENOENT errors for anything (they happen, strangely enough - possibly
  76  * due to races between multiple dying UML threads).
  77  */
  78 static int remove_files_and_dir(char *dir)
  79 {
  80         DIR *directory;
  81         struct dirent *ent;
  82         int len;
  83         char file[256];
  84         int ret;
  85
  86         directory = opendir(dir);
  87         if (directory == NULL) {
  88                 if (errno != ENOENT)
  89                         return -errno;
  90                 else
  91                         return 0;
  92         }
  93
  94         while ((ent = readdir(directory)) != NULL) {
  95                 if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
  96                         continue;
  97                 len = strlen(dir) + sizeof("/") + strlen(ent->d_name) + 1;
  98                 if (len > sizeof(file)) {
  99                         ret = -E2BIG;
 100                         goto out;
 101                 }
 102
 103                 sprintf(file, "%s/%s", dir, ent->d_name);
 104                 if (unlink(file) < 0 && errno != ENOENT) {
 105                         ret = -errno;
 106                         goto out;
 107                 }
 108         }
 109
 110         if (rmdir(dir) < 0 && errno != ENOENT) {
 111                 ret = -errno;
 112                 goto out;
 113         }
 114
 115         ret = 0;
 116 out:
 117         closedir(directory);
 118         return ret;
 119 }
 120
 121 /*
 122  * This says that there isn't already a user of the specified directory even if
 123  * there are errors during the checking.  This is because if these errors
 124  * happen, the directory is unusable by the pre-existing UML, so we might as
 125  * well take it over.  This could happen either by
 126  *      the existing UML somehow corrupting its umid directory
 127  *      something other than UML sticking stuff in the directory
 128  *      this boot racing with a shutdown of the other UML
 129  * In any of these cases, the directory isn't useful for anything else.
 130  *
 131  * Boolean return: 1 if in use, 0 otherwise.
 132  */
 133 static inline int is_umdir_used(char *dir)
 134 {
 135         char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
 136         char pid[sizeof("nnnnn\0")], *end;
 137         int dead, fd, p, n, err;
 138
 139         n = snprintf(file, sizeof(file), "%s/pid", dir);
 140         if (n >= sizeof(file)) {
 141                 printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
 142                 err = -E2BIG;
 143                 goto out;
 144         }
 145
 146         dead = 0;
 147         fd = open(file, O_RDONLY);
 148         if (fd < 0) {
 149                 fd = -errno;
 150                 if (fd != -ENOENT) {
 151                         printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
 152                                "file '%s', err = %d\n", file, -fd);
 153                 }
 154                 goto out;
 155         }
 156
 157         err = 0;
 158         n = read(fd, pid, sizeof(pid));
 159         if (n < 0) {
 160                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 161                        "'%s', err = %d\n", file, errno);
 162                 goto out_close;
 163         } else if (n == 0) {
 164                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 165                        "'%s', 0-byte read\n", file);
 166                 goto out_close;
 167         }
 168
 169         p = strtoul(pid, &end, 0);
 170         if (end == pid) {
 171                 printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
 172                        "'%s', errno = %d\n", file, errno);
 173                 goto out_close;
 174         }
 175
 176         if ((kill(p, 0) == 0) || (errno != ESRCH)) {
 177                 printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
 178                        umid, p);
 179                 return 1;
 180         }
 181
 182 out_close:
 183         close(fd);
 184 out:
 185         return 0;
 186 }
 187
 188 /*
 189  * Try to remove the directory @dir unless it's in use.
 190  * Precondition: @dir exists.
 191  * Returns 0 for success, < 0 for failure in removal or if the directory is in
 192  * use.
 193  */
 194 static int umdir_take_if_dead(char *dir)
 195 {
 196         int ret;
 197         if (is_umdir_used(dir))
 198                 return -EEXIST;
 199
 200         ret = remove_files_and_dir(dir);
 201         if (ret) {
 202                 printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
 203                        "failed with err = %d\n", ret);
 204         }
 205         return ret;
 206 }
 207
 208 static void __init create_pid_file(void)
 209 {
 210         char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
 211         char pid[sizeof("nnnnn\0")];
 212         int fd, n;
 213
 214         if (umid_file_name("pid", file, sizeof(file)))
 215                 return;
 216
 217         fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
 218         if (fd < 0) {
 219                 printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
 220                        "%s\n", file, strerror(errno));
 221                 return;
 222         }
 223
 224         snprintf(pid, sizeof(pid), "%d\n", getpid());
 225         n = write(fd, pid, strlen(pid));
 226         if (n != strlen(pid))
 227                 printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
 228                        errno);
 229
 230         close(fd);
 231 }
 232
 233 int __init set_umid(char *name)
 234 {
 235         if (strlen(name) > UMID_LEN - 1)
 236                 return -E2BIG;
 237
 238         strlcpy(umid, name, sizeof(umid));
 239
 240         return 0;
 241 }
 242
 243 /* Changed in make_umid, which is called during early boot */
 244 static int umid_setup = 0;
 245
 246 static int __init make_umid(void)
 247 {
 248         int fd, err;
 249         char tmp[256];
 250
 251         if (umid_setup)
 252                 return 0;
 253
 254         make_uml_dir();
 255
 256         if (*umid == '\0') {
 257                 strlcpy(tmp, uml_dir, sizeof(tmp));
 258                 strlcat(tmp, "XXXXXX", sizeof(tmp));
 259                 fd = mkstemp(tmp);
 260                 if (fd < 0) {
 261                         printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
 262                                "%s\n", tmp, strerror(errno));
 263                         err = -errno;
 264                         goto err;
 265                 }
 266
 267                 close(fd);
 268
 269                 set_umid(&tmp[strlen(uml_dir)]);
 270
 271                 /*
 272                  * There's a nice tiny little race between this unlink and
 273                  * the mkdir below.  It'd be nice if there were a mkstemp
 274                  * for directories.
 275                  */
 276                 if (unlink(tmp)) {
 277                         err = -errno;
 278                         goto err;
 279                 }
 280         }
 281
 282         snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
 283         err = mkdir(tmp, 0777);
 284         if (err < 0) {
 285                 err = -errno;
 286                 if (err != -EEXIST)
 287                         goto err;
 288
 289                 if (umdir_take_if_dead(tmp) < 0)
 290                         goto err;
 291
 292                 err = mkdir(tmp, 0777);
 293         }
 294         if (err) {
 295                 err = -errno;
 296                 printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
 297                        errno);
 298                 goto err;
 299         }
 300
 301         umid_setup = 1;
 302
 303         create_pid_file();
 304
 305         err = 0;
 306  err:
 307         return err;
 308 }
 309
 310 static int __init make_umid_init(void)
 311 {
 312         if (!make_umid())
 313                 return 0;
 314
 315         /*
 316          * If initializing with the given umid failed, then try again with
 317          * a random one.
 318          */
 319         printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
 320                "random umid\n", umid);
 321         *umid = '\0';
 322         make_umid();
 323
 324         return 0;
 325 }
 326
 327 __initcall(make_umid_init);
 328
 329 int __init umid_file_name(char *name, char *buf, int len)
 330 {
 331         int n, err;
 332
 333         err = make_umid();
 334         if (err)
 335                 return err;
 336
 337         n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
 338         if (n >= len) {
 339                 printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
 340                 return -E2BIG;
 341         }
 342
 343         return 0;
 344 }
 345
 346 char *get_umid(void)
 347 {
 348         return umid;
 349 }
 350
 351 static int __init set_uml_dir(char *name, int *add)
 352 {
 353         if (*name == '\0') {
 354                 printf("uml_dir can't be an empty string\n");
 355                 return 0;
 356         }
 357
 358         if (name[strlen(name) - 1] == '/') {
 359                 uml_dir = name;
 360                 return 0;
 361         }
 362
 363         uml_dir = malloc(strlen(name) + 2);
 364         if (uml_dir == NULL) {
 365                 printf("Failed to malloc uml_dir - error = %d\n", errno);
 366
 367                 /*
 368                  * Return 0 here because do_initcalls doesn't look at
 369                  * the return value.
 370                  */
 371                 return 0;
 372         }
 373         sprintf(uml_dir, "%s/", name);
 374
 375         return 0;
 376 }
 377
 378 __uml_setup("uml_dir=", set_uml_dir,
 379 "uml_dir=<directory>\n"
 380 "    The location to place the pid and umid files.\n\n"
 381 );
 382
 383 static void remove_umid_dir(void)
 384 {
 385         char dir[strlen(uml_dir) + UMID_LEN + 1], err;
 386
 387         sprintf(dir, "%s%s", uml_dir, umid);
 388         err = remove_files_and_dir(dir);
 389         if (err)
 390                 printf("remove_umid_dir - remove_files_and_dir failed with "
 391                        "err = %d\n", err);
 392 }
 393
 394 __uml_exitcall(remove_umid_dir);