fd.c

   1 /*
   2  * Copyright (C) 2006-2008 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file fd.c Helper functions for file descriptor handling. */
   8
   9 #include <sys/types.h>
  10 #include <dirent.h>
  11 #include <sys/mman.h>
  12 #include <fcntl.h>
  13 #include <sys/select.h>
  14
  15 #include "para.h"
  16 #include "error.h"
  17
  18 /**
  19  * Write a buffer to a file descriptor, re-write on short writes.
  20  *
  21  * \param fd The file descriptor.
  22  * \param buf The buffer to be sent.
  23  * \param len The length of \a buf.
  24  *
  25  * \return Standard. In any case, the number of bytes that have been written is
  26  * stored in \a len.
  27  */
  28 int write_all(int fd, const char *buf, size_t *len)
  29 {
  30         size_t total = *len;
  31
  32         assert(total);
  33         *len = 0;
  34         while (*len < total) {
  35                 int ret = write(fd, buf + *len, total - *len);
  36                 if (ret == -1)
  37                         return -ERRNO_TO_PARA_ERROR(errno);
  38                 *len += ret;
  39         }
  40         return 1;
  41 }
  42
  43 /**
  44  * Check whether a file exists.
  45  *
  46  * \param fn The file name.
  47  *
  48  * \return Non-zero iff file exists.
  49  */
  50 int file_exists(const char *fn)
  51 {
  52         struct stat statbuf;
  53
  54         return !stat(fn, &statbuf);
  55 }
  56
  57 /**
  58  * Paraslash's wrapper for select(2).
  59  *
  60  * It calls select(2) (with no exceptfds) and starts over if select() was
  61  * interrupted by a signal.
  62  *
  63  * \param n The highest-numbered descriptor in any of the two sets, plus 1.
  64  * \param readfds fds that should be checked for readability.
  65  * \param writefds fds that should be checked for writablility.
  66  * \param timeout_tv upper bound on the amount of time elapsed before select()
  67  * returns.
  68  *
  69  * \return The return value of the underlying select() call on success, the
  70  * negative system error code on errors.
  71  *
  72  * All arguments are passed verbatim to select(2).
  73  * \sa select(2) select_tut(2).
  74  */
  75 int para_select(int n, fd_set *readfds, fd_set *writefds,
  76                 struct timeval *timeout_tv)
  77 {
  78         int ret, err;
  79         do {
  80                 ret = select(n, readfds, writefds, NULL, timeout_tv);
  81                 err = errno;
  82         } while (ret < 0 && err == EINTR);
  83         if (ret < 0)
  84                 return -ERRNO_TO_PARA_ERROR(errno);
  85         return ret;
  86 }
  87
  88 /**
  89  * Set a file descriptor to blocking mode.
  90  *
  91  * \param fd The file descriptor.
  92  *
  93  * \return Standard.
  94  */
  95 __must_check int mark_fd_blocking(int fd)
  96 {
  97         int flags = fcntl(fd, F_GETFL);
  98         if (flags < 0)
  99                 return -ERRNO_TO_PARA_ERROR(errno);
 100         flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
 101         if (flags < 0)
 102                 return -ERRNO_TO_PARA_ERROR(errno);
 103         return 1;
 104 }
 105
 106 /**
 107  * Set a file descriptor to non-blocking mode.
 108  *
 109  * \param fd The file descriptor.
 110  *
 111  * \return Standard.
 112  */
 113 __must_check int mark_fd_nonblocking(int fd)
 114 {
 115         int flags = fcntl(fd, F_GETFL);
 116         if (flags < 0)
 117                 return -ERRNO_TO_PARA_ERROR(errno);
 118         flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
 119         if (flags < 0)
 120                 return -ERRNO_TO_PARA_ERROR(errno);
 121         return 1;
 122 }
 123
 124 /**
 125  * Set a file descriptor in a fd_set.
 126  *
 127  * \param fd The file descriptor to be set.
 128  * \param fds The file descriptor set.
 129  * \param max_fileno Highest-numbered file descriptor.
 130  *
 131  * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
 132  * return, \a max_fileno contains the maximum of the old_value and \a fd.
 133  *
 134  * \sa para_select.
 135 */
 136 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
 137 {
 138
 139         if (fd < 0 || fd >= FD_SETSIZE) {
 140                 PARA_EMERG_LOG("fatal: tried to add invalid fd %d\n", fd);
 141                 exit(EXIT_FAILURE);
 142         }
 143 #if 0
 144         {
 145                 int flags = fcntl(fd, F_GETFL);
 146                 if (!(flags & O_NONBLOCK)) {
 147                         PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
 148                         exit(EXIT_FAILURE);
 149                 }
 150         }
 151 #endif
 152         FD_SET(fd, fds);
 153         *max_fileno = PARA_MAX(*max_fileno, fd);
 154 }
 155
 156 /**
 157  * Paraslash's wrapper for fgets(3).
 158  *
 159  * \param line Pointer to the buffer to store the line.
 160  * \param size The size of the buffer given by \a line.
 161  * \param f The stream to read from.
 162  *
 163  * \return Unlike the standard fgets() function, an integer value
 164  * is returned. On success, this function returns 1. On errors, -E_FGETS
 165  * is returned. A zero return value indicates an end of file condition.
 166  */
 167 __must_check int para_fgets(char *line, int size, FILE *f)
 168 {
 169 again:
 170         if (fgets(line, size, f))
 171                 return 1;
 172         if (feof(f))
 173                 return 0;
 174         if (!ferror(f))
 175                 return -E_FGETS;
 176         if (errno != EINTR) {
 177                 PARA_ERROR_LOG("%s\n", strerror(errno));
 178                 return -E_FGETS;
 179         }
 180         clearerr(f);
 181         goto again;
 182 }
 183
 184 /**
 185  * Paraslash's wrapper for mmap.
 186  *
 187  * \param length Number of bytes to mmap.
 188  * \param prot Either PROT_NONE or the bitwise OR of one or more of
 189  * PROT_EXEC PROT_READ PROT_WRITE.
 190  * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
 191  * \param fd The file to mmap from.
 192  * \param offset Mmap start.
 193  *
 194  * \return This function either returns a valid pointer to the mapped area
 195  * or calls exit() on errors.
 196  */
 197 void *para_mmap(size_t length, int prot, int flags, int fd, off_t offset)
 198 {
 199         void *ret = mmap(NULL, length, prot, flags, fd, offset);
 200         if (ret != MAP_FAILED)
 201                 return ret;
 202         PARA_EMERG_LOG("mmap failed: %s\n", strerror(errno));
 203         PARA_EMERG_LOG("length: %zu, flags: %d, fd: %d, offset: %zu\n",
 204                 length, flags, fd, (size_t)offset);
 205         exit(EXIT_FAILURE);
 206 }
 207
 208 /**
 209  * Wrapper for the open(2) system call.
 210  *
 211  * \param path The filename.
 212  * \param flags The usual open(2) flags.
 213  * \param mode Specifies the permissions to use.
 214  *
 215  * The mode parameter must be specified when O_CREAT is in the flags, and is
 216  * ignored otherwise.
 217  *
 218  * \return The file descriptor on success, negative on errors.
 219  *
 220  * \sa open(2).
 221  */
 222 int para_open(const char *path, int flags, mode_t mode)
 223 {
 224         int ret = open(path, flags, mode);
 225
 226         if (ret >= 0)
 227                 return ret;
 228         return -ERRNO_TO_PARA_ERROR(errno);
 229 }
 230
 231 /**
 232  * Wrapper for chdir(2).
 233  *
 234  * \param path The specified directory.
 235  *
 236  * \return Standard.
 237  */
 238 int para_chdir(const char *path)
 239 {
 240         int ret = chdir(path);
 241
 242         if (ret >= 0)
 243                 return 1;
 244         return -ERRNO_TO_PARA_ERROR(errno);
 245 }
 246
 247 /**
 248  * Save the cwd and open a given directory.
 249  *
 250  * \param dirname Path to the directory to open.
 251  * \param dir Result pointer.
 252  * \param cwd File descriptor of the current working directory.
 253  *
 254  * \return Standard.
 255  *
 256  * Opening the current directory (".") and calling fchdir() to return is
 257  * usually faster and more reliable than saving cwd in some buffer and calling
 258  * chdir() afterwards.
 259  *
 260  * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
 261  * stored in \a cwd. If the function returns success, and \a cwd is not \p
 262  * NULL, the caller must close this file descriptor (probably after calling
 263  * fchdir(*cwd)).
 264  *
 265  * On errors, the function undos everything, so the caller needs neither close
 266  * any files, nor change back to the original working directory.
 267  *
 268  * \sa getcwd(3).
 269  *
 270  */
 271 int para_opendir(const char *dirname, DIR **dir, int *cwd)
 272 {
 273         int ret;
 274
 275         if (cwd) {
 276                 ret = para_open(".", O_RDONLY, 0);
 277                 if (ret < 0)
 278                         return ret;
 279                 *cwd = ret;
 280         }
 281         ret = para_chdir(dirname);
 282         if (ret < 0)
 283                 goto close_cwd;
 284         *dir = opendir(".");
 285         if (*dir)
 286                 return 1;
 287         ret = -ERRNO_TO_PARA_ERROR(errno);
 288 /* Ignore return value of fchdir() and close(). We're busted anyway. */
 289         if (cwd)
 290                 fchdir(*cwd);
 291 close_cwd:
 292         if (cwd)
 293                 close(*cwd);
 294         return ret;
 295 }
 296
 297 /**
 298  * A wrapper for fchdir().
 299  *
 300  * \param fd An open file descriptor.
 301  *
 302  * \return Standard.
 303  */
 304 int para_fchdir(int fd)
 305 {
 306         if (fchdir(fd) < 0)
 307                 return -ERRNO_TO_PARA_ERROR(errno);
 308         return 1;
 309 }
 310
 311 /**
 312  * A wrapper for mkdir(2).
 313  *
 314  * \param path Name of the directory to create.
 315  * \param mode The permissions to use.
 316  *
 317  * \return Standard.
 318  */
 319 int para_mkdir(const char *path, mode_t mode)
 320 {
 321         if (!mkdir(path, mode))
 322                 return 1;
 323         return -ERRNO_TO_PARA_ERROR(errno);
 324 }
 325
 326 /**
 327  * Open a file and map it into memory.
 328  *
 329  * \param path Name of the regular file to map.
 330  * \param open_mode Either \p O_RDONLY or \p O_RDWR.
 331  * \param map On success, the mapping is returned here.
 332  * \param size size of the mapping.
 333  * \param fd_ptr The file descriptor of the mapping.
 334  *
 335  * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
 336  * open call is closed after mmap().  Otherwise the file is kept open and the
 337  * file descriptor is returned in \a fd_ptr.
 338  *
 339  * \return Standard.
 340  *
 341  * \sa para_open(), mmap(2).
 342  */
 343 int mmap_full_file(const char *path, int open_mode, void **map,
 344                 size_t *size, int *fd_ptr)
 345 {
 346         int fd, ret, mmap_prot, mmap_flags;
 347         struct stat file_status;
 348
 349         if (open_mode == O_RDONLY) {
 350                 mmap_prot = PROT_READ;
 351                 mmap_flags = MAP_PRIVATE;
 352         } else {
 353                 mmap_prot = PROT_READ | PROT_WRITE;
 354                 mmap_flags = MAP_SHARED;
 355         }
 356         ret = para_open(path, open_mode, 0);
 357         if (ret < 0)
 358                 return ret;
 359         fd = ret;
 360         if (fstat(fd, &file_status) < 0) {
 361                 ret = -ERRNO_TO_PARA_ERROR(errno);
 362                 goto out;
 363         }
 364         *size = file_status.st_size;
 365         ret = -E_EMPTY;
 366         PARA_DEBUG_LOG("%s: size %zu\n", path, *size);
 367         if (!*size)
 368                 goto out;
 369         *map = mmap(NULL, *size, mmap_prot, mmap_flags, fd, 0);
 370         if (*map == MAP_FAILED) {
 371                 *map = NULL;
 372                 ret = -E_MMAP;
 373                 goto out;
 374         }
 375         ret = 1;
 376 out:
 377         if (ret < 0 || !fd_ptr)
 378                 close(fd);
 379         else
 380                 *fd_ptr = fd;
 381         return ret;
 382 }
 383
 384 /**
 385  * A wrapper for munmap(2).
 386  *
 387  * \param start The start address of the memory mapping.
 388  * \param length The size of the mapping.
 389  *
 390  * \return Positive on success, \p -E_MUNMAP on errors.
 391  *
 392  * \sa munmap(2), mmap_full_file().
 393  */
 394 int para_munmap(void *start, size_t length)
 395 {
 396         int err;
 397         if (munmap(start, length) >= 0)
 398                 return 1;
 399         err = errno;
 400         PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
 401                 strerror(err));
 402         return -ERRNO_TO_PARA_ERROR(err);
 403 }
 404
 405 /**
 406  * Check a file descriptor for writability.
 407  *
 408  * \param fd The file descriptor.
 409  *
 410  * \return positive if fd is ready for writing, zero if it isn't, negative if
 411  * an error occurred.
 412  */
 413
 414 int write_ok(int fd)
 415 {
 416         struct timeval tv = {0, 0};
 417         fd_set wfds;
 418         int ret;
 419 again:
 420         FD_ZERO(&wfds);
 421         FD_SET(fd, &wfds);
 422         tv.tv_sec = 0;
 423         tv.tv_usec = 0;
 424         ret = select(fd + 1, NULL, &wfds, NULL, &tv);
 425         if (ret < 0 && errno == EINTR)
 426                 goto again;
 427         return ret;
 428 }
 429
 430 /**
 431  * Ensure that file descriptors 0, 1, and 2 are valid.
 432  *
 433  * Common approach that opens /dev/null until it gets a file descriptor greater
 434  * than two.
 435  *
 436  * \sa okir's Black Hats Manual.
 437  */
 438 void valid_fd_012(void)
 439 {
 440         while (1) {
 441                 int fd = open("/dev/null", O_RDWR);
 442                 if (fd < 0)
 443                         exit(EXIT_FAILURE);
 444                 if (fd > 2) {
 445                         close(fd);
 446                         break;
 447                 }
 448         }
 449 }