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 "kern_constants.h"
  17 #include "os.h"
  18 #include "user.h"
  19
  20 #define UML_DIR "~/.uml/"
  21
  22 #define UMID_LEN 64
  23
  24 /* Changed by set_umid, which is run early in boot */
  25 static char umid[UMID_LEN] = { 0 };
  26
  27 /* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
  28 static char *uml_dir = UML_DIR;
  29
  30 static int __init make_uml_dir(void)
  31 {
  32         char dir[512] = { '\0' };
  33         int len, err;
  34
  35         if (*uml_dir == '~') {
  36                 char *home = getenv("HOME");
  37
  38                 err = -ENOENT;
  39                 if (home == NULL) {
  40                         printk(UM_KERN_ERR "make_uml_dir : no value in "
  41                                "environment for $HOME\n");
  42                         goto err;
  43                 }
  44                 strlcpy(dir, home, sizeof(dir));
  45                 uml_dir++;
  46         }
  47         strlcat(dir, uml_dir, sizeof(dir));
  48         len = strlen(dir);
  49         if (len > 0 && dir[len - 1] != '/')
  50                 strlcat(dir, "/", sizeof(dir));
  51
  52         err = -ENOMEM;
  53         uml_dir = malloc(strlen(dir) + 1);
  54         if (uml_dir == NULL) {
  55                 printf("make_uml_dir : malloc failed, errno = %d\n", errno);
  56                 goto err;
  57         }
  58         strcpy(uml_dir, dir);
  59
  60         if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
  61                 printf("Failed to mkdir '%s': %s\n", uml_dir, strerror(errno));
  62                 err = -errno;
  63                 goto err_free;
  64         }
  65         return 0;
  66
  67 err_free:
  68         free(uml_dir);
  69 err:
  70         uml_dir = NULL;
  71         return err;
  72 }
  73
  74 /*
  75  * Unlinks the files contained in @dir and then removes @dir.
  76  * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
  77  * ignore ENOENT errors for anything (they happen, strangely enough - possibly
  78  * due to races between multiple dying UML threads).
  79  */
  80 static int remove_files_and_dir(char *dir)
  81 {
  82         DIR *directory;
  83         struct dirent *ent;
  84         int len;
  85         char file[256];
  86         int ret;
  87
  88         directory = opendir(dir);
  89         if (directory == NULL) {
  90                 if (errno != ENOENT)
  91                         return -errno;
  92                 else
  93                         return 0;
  94         }
  95
  96         while ((ent = readdir(directory)) != NULL) {
  97                 if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
  98                         continue;
  99                 len = strlen(dir) + sizeof("/") + strlen(ent->d_name) + 1;
 100                 if (len > sizeof(file)) {
 101                         ret = -E2BIG;
 102                         goto out;
 103                 }
 104
 105                 sprintf(file, "%s/%s", dir, ent->d_name);
 106                 if (unlink(file) < 0 && errno != ENOENT) {
 107                         ret = -errno;
 108                         goto out;
 109                 }
 110         }
 111
 112         if (rmdir(dir) < 0 && errno != ENOENT) {
 113                 ret = -errno;
 114                 goto out;
 115         }
 116
 117         ret = 0;
 118 out:
 119         closedir(directory);
 120         return ret;
 121 }
 122
 123 /*
 124  * This says that there isn't already a user of the specified directory even if
 125  * there are errors during the checking.  This is because if these errors
 126  * happen, the directory is unusable by the pre-existing UML, so we might as
 127  * well take it over.  This could happen either by
 128  *      the existing UML somehow corrupting its umid directory
 129  *      something other than UML sticking stuff in the directory
 130  *      this boot racing with a shutdown of the other UML
 131  * In any of these cases, the directory isn't useful for anything else.
 132  *
 133  * Boolean return: 1 if in use, 0 otherwise.
 134  */
 135 static inline int is_umdir_used(char *dir)
 136 {
 137         char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
 138         char pid[sizeof("nnnnn\0")], *end;
 139         int dead, fd, p, n, err;
 140
 141         n = snprintf(file, sizeof(file), "%s/pid", dir);
 142         if (n >= sizeof(file)) {
 143                 printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
 144                 err = -E2BIG;
 145                 goto out;
 146         }
 147
 148         dead = 0;
 149         fd = open(file, O_RDONLY);
 150         if (fd < 0) {
 151                 fd = -errno;
 152                 if (fd != -ENOENT) {
 153                         printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
 154                                "file '%s', err = %d\n", file, -fd);
 155                 }
 156                 goto out;
 157         }
 158
 159         err = 0;
 160         n = read(fd, pid, sizeof(pid));
 161         if (n < 0) {
 162                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 163                        "'%s', err = %d\n", file, errno);
 164                 goto out_close;
 165         } else if (n == 0) {
 166                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 167                        "'%s', 0-byte read\n", file);
 168                 goto out_close;
 169         }
 170
 171         p = strtoul(pid, &end, 0);
 172         if (end == pid) {
 173                 printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
 174                        "'%s', errno = %d\n", file, errno);
 175                 goto out_close;
 176         }
 177
 178         if ((kill(p, 0) == 0) || (errno != ESRCH)) {
 179                 printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
 180                        umid, p);
 181                 return 1;
 182         }
 183
 184 out_close:
 185         close(fd);
 186 out:
 187         return 0;
 188 }
 189
 190 /*
 191  * Try to remove the directory @dir unless it's in use.
 192  * Precondition: @dir exists.
 193  * Returns 0 for success, < 0 for failure in removal or if the directory is in
 194  * use.
 195  */
 196 static int umdir_take_if_dead(char *dir)
 197 {
 198         int ret;
 199         if (is_umdir_used(dir))
 200                 return -EEXIST;
 201
 202         ret = remove_files_and_dir(dir);
 203         if (ret) {
 204                 printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
 205                        "failed with err = %d\n", ret);
 206         }
 207         return ret;
 208 }
 209
 210 static void __init create_pid_file(void)
 211 {
 212         char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
 213         char pid[sizeof("nnnnn\0")];
 214         int fd, n;
 215
 216         if (umid_file_name("pid", file, sizeof(file)))
 217                 return;
 218
 219         fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
 220         if (fd < 0) {
 221                 printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
 222                        "%s\n", file, strerror(errno));
 223                 return;
 224         }
 225
 226         snprintf(pid, sizeof(pid), "%d\n", getpid());
 227         n = write(fd, pid, strlen(pid));
 228         if (n != strlen(pid))
 229                 printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
 230                        errno);
 231
 232         close(fd);
 233 }
 234
 235 int __init set_umid(char *name)
 236 {
 237         if (strlen(name) > UMID_LEN - 1)
 238                 return -E2BIG;
 239
 240         strlcpy(umid, name, sizeof(umid));
 241
 242         return 0;
 243 }
 244
 245 /* Changed in make_umid, which is called during early boot */
 246 static int umid_setup = 0;
 247
 248 int __init make_umid(void)
 249 {
 250         int fd, err;
 251         char tmp[256];
 252
 253         if (umid_setup)
 254                 return 0;
 255
 256         make_uml_dir();
 257
 258         if (*umid == '\0') {
 259                 strlcpy(tmp, uml_dir, sizeof(tmp));
 260                 strlcat(tmp, "XXXXXX", sizeof(tmp));
 261                 fd = mkstemp(tmp);
 262                 if (fd < 0) {
 263                         printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
 264                                "%s\n", tmp, strerror(errno));
 265                         err = -errno;
 266                         goto err;
 267                 }
 268
 269                 close(fd);
 270
 271                 set_umid(&tmp[strlen(uml_dir)]);
 272
 273                 /*
 274                  * There's a nice tiny little race between this unlink and
 275                  * the mkdir below.  It'd be nice if there were a mkstemp
 276                  * for directories.
 277                  */
 278                 if (unlink(tmp)) {
 279                         err = -errno;
 280                         goto err;
 281                 }
 282         }
 283
 284         snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
 285         err = mkdir(tmp, 0777);
 286         if (err < 0) {
 287                 err = -errno;
 288                 if (err != -EEXIST)
 289                         goto err;
 290
 291                 if (umdir_take_if_dead(tmp) < 0)
 292                         goto err;
 293
 294                 err = mkdir(tmp, 0777);
 295         }
 296         if (err) {
 297                 err = -errno;
 298                 printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
 299                        errno);
 300                 goto err;
 301         }
 302
 303         umid_setup = 1;
 304
 305         create_pid_file();
 306
 307         err = 0;
 308  err:
 309         return err;
 310 }
 311
 312 static int __init make_umid_init(void)
 313 {
 314         if (!make_umid())
 315                 return 0;
 316
 317         /*
 318          * If initializing with the given umid failed, then try again with
 319          * a random one.
 320          */
 321         printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
 322                "random umid\n", umid);
 323         *umid = '\0';
 324         make_umid();
 325
 326         return 0;
 327 }
 328
 329 __initcall(make_umid_init);
 330
 331 int __init umid_file_name(char *name, char *buf, int len)
 332 {
 333         int n, err;
 334
 335         err = make_umid();
 336         if (err)
 337                 return err;
 338
 339         n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
 340         if (n >= len) {
 341                 printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
 342                 return -E2BIG;
 343         }
 344
 345         return 0;
 346 }
 347
 348 char *get_umid(void)
 349 {
 350         return umid;
 351 }
 352
 353 static int __init set_uml_dir(char *name, int *add)
 354 {
 355         if (*name == '\0') {
 356                 printf("uml_dir can't be an empty string\n");
 357                 return 0;
 358         }
 359
 360         if (name[strlen(name) - 1] == '/') {
 361                 uml_dir = name;
 362                 return 0;
 363         }
 364
 365         uml_dir = malloc(strlen(name) + 2);
 366         if (uml_dir == NULL) {
 367                 printf("Failed to malloc uml_dir - error = %d\n", errno);
 368
 369                 /*
 370                  * Return 0 here because do_initcalls doesn't look at
 371                  * the return value.
 372                  */
 373                 return 0;
 374         }
 375         sprintf(uml_dir, "%s/", name);
 376
 377         return 0;
 378 }
 379
 380 __uml_setup("uml_dir=", set_uml_dir,
 381 "uml_dir=<directory>\n"
 382 "    The location to place the pid and umid files.\n\n"
 383 );
 384
 385 static void remove_umid_dir(void)
 386 {
 387         char dir[strlen(uml_dir) + UMID_LEN + 1], err;
 388
 389         sprintf(dir, "%s%s", uml_dir, umid);
 390         err = remove_files_and_dir(dir);
 391         if (err)
 392                 printf("remove_umid_dir - remove_files_and_dir failed with "
 393                        "err = %d\n", err);
 394 }
 395
 396 __uml_exitcall(remove_umid_dir);