fd.c

   1 /*
   2  * Copyright (C) 2006-2009 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  * Write a buffer to a non-blocking file descriptor.
  45  *
  46  * \param fd The file descriptor.
  47  * \param buf the buffer to write.
  48  * \param len the number of bytes of \a buf.
  49  * \param max_bytes_per_write Do not write more than that many bytes at once.
  50  *
  51  * If \a max_bytes_per_write is non-zero, do not send more than that many bytes
  52  * per write().
  53  *
  54  * EAGAIN is not considered an error condition.  For example CCID3 has a
  55  * sending wait queue which fills up and is emptied asynchronously. The EAGAIN
  56  * case means that there is currently no space in the wait queue, but this can
  57  * change at any moment.
  58  *
  59  * \return Negative on errors, number of bytes written else.
  60  */
  61 int write_nonblock(int fd, const char *buf, size_t len,
  62                 size_t max_bytes_per_write)
  63 {
  64         size_t written = 0;
  65         int ret = 0;
  66
  67         while (written < len) {
  68                 size_t num = len - written;
  69
  70                 if (max_bytes_per_write && max_bytes_per_write < num)
  71                         num = max_bytes_per_write;
  72                 ret = write(fd, buf + written, num);
  73                 if (ret < 0 && errno == EAGAIN)
  74                         return written;
  75                 if (ret < 0)
  76                         return -ERRNO_TO_PARA_ERROR(errno);
  77                 written += ret;
  78         }
  79         return written;
  80 }
  81
  82 /**
  83  * Check whether a file exists.
  84  *
  85  * \param fn The file name.
  86  *
  87  * \return Non-zero iff file exists.
  88  */
  89 int file_exists(const char *fn)
  90 {
  91         struct stat statbuf;
  92
  93         return !stat(fn, &statbuf);
  94 }
  95
  96 /**
  97  * Paraslash's wrapper for select(2).
  98  *
  99  * It calls select(2) (with no exceptfds) and starts over if select() was
 100  * interrupted by a signal.
 101  *
 102  * \param n The highest-numbered descriptor in any of the two sets, plus 1.
 103  * \param readfds fds that should be checked for readability.
 104  * \param writefds fds that should be checked for writablility.
 105  * \param timeout_tv upper bound on the amount of time elapsed before select()
 106  * returns.
 107  *
 108  * \return The return value of the underlying select() call on success, the
 109  * negative system error code on errors.
 110  *
 111  * All arguments are passed verbatim to select(2).
 112  * \sa select(2) select_tut(2).
 113  */
 114 int para_select(int n, fd_set *readfds, fd_set *writefds,
 115                 struct timeval *timeout_tv)
 116 {
 117         int ret, err;
 118         do {
 119                 ret = select(n, readfds, writefds, NULL, timeout_tv);
 120                 err = errno;
 121         } while (ret < 0 && err == EINTR);
 122         if (ret < 0)
 123                 return -ERRNO_TO_PARA_ERROR(errno);
 124         return ret;
 125 }
 126
 127 /**
 128  * Set a file descriptor to blocking mode.
 129  *
 130  * \param fd The file descriptor.
 131  *
 132  * \return Standard.
 133  */
 134 __must_check int mark_fd_blocking(int fd)
 135 {
 136         int flags = fcntl(fd, F_GETFL);
 137         if (flags < 0)
 138                 return -ERRNO_TO_PARA_ERROR(errno);
 139         flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
 140         if (flags < 0)
 141                 return -ERRNO_TO_PARA_ERROR(errno);
 142         return 1;
 143 }
 144
 145 /**
 146  * Set a file descriptor to non-blocking mode.
 147  *
 148  * \param fd The file descriptor.
 149  *
 150  * \return Standard.
 151  */
 152 __must_check int mark_fd_nonblocking(int fd)
 153 {
 154         int flags = fcntl(fd, F_GETFL);
 155         if (flags < 0)
 156                 return -ERRNO_TO_PARA_ERROR(errno);
 157         flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
 158         if (flags < 0)
 159                 return -ERRNO_TO_PARA_ERROR(errno);
 160         return 1;
 161 }
 162
 163 /**
 164  * Set a file descriptor in a fd_set.
 165  *
 166  * \param fd The file descriptor to be set.
 167  * \param fds The file descriptor set.
 168  * \param max_fileno Highest-numbered file descriptor.
 169  *
 170  * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
 171  * return, \a max_fileno contains the maximum of the old_value and \a fd.
 172  *
 173  * \sa para_select.
 174 */
 175 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
 176 {
 177         assert(fd >= 0 && fd < FD_SETSIZE);
 178 #if 0
 179         {
 180                 int flags = fcntl(fd, F_GETFL);
 181                 if (!(flags & O_NONBLOCK)) {
 182                         PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
 183                         exit(EXIT_FAILURE);
 184                 }
 185         }
 186 #endif
 187         FD_SET(fd, fds);
 188         *max_fileno = PARA_MAX(*max_fileno, fd);
 189 }
 190
 191 /**
 192  * Paraslash's wrapper for fgets(3).
 193  *
 194  * \param line Pointer to the buffer to store the line.
 195  * \param size The size of the buffer given by \a line.
 196  * \param f The stream to read from.
 197  *
 198  * \return Unlike the standard fgets() function, an integer value
 199  * is returned. On success, this function returns 1. On errors, -E_FGETS
 200  * is returned. A zero return value indicates an end of file condition.
 201  */
 202 __must_check int para_fgets(char *line, int size, FILE *f)
 203 {
 204 again:
 205         if (fgets(line, size, f))
 206                 return 1;
 207         if (feof(f))
 208                 return 0;
 209         if (!ferror(f))
 210                 return -E_FGETS;
 211         if (errno != EINTR) {
 212                 PARA_ERROR_LOG("%s\n", strerror(errno));
 213                 return -E_FGETS;
 214         }
 215         clearerr(f);
 216         goto again;
 217 }
 218
 219 /**
 220  * Paraslash's wrapper for mmap.
 221  *
 222  * \param length Number of bytes to mmap.
 223  * \param prot Either PROT_NONE or the bitwise OR of one or more of
 224  * PROT_EXEC PROT_READ PROT_WRITE.
 225  * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
 226  * \param fd The file to mmap from.
 227  * \param offset Mmap start.
 228  * \param map Result pointer.
 229  *
 230  * \return Standard.
 231  *
 232  * \sa mmap(2).
 233  */
 234 int para_mmap(size_t length, int prot, int flags, int fd, off_t offset,
 235                 void *map)
 236 {
 237         void **m = map;
 238
 239         errno = EINVAL;
 240         if (!length)
 241                 goto err;
 242         *m = mmap(NULL, length, prot, flags, fd, offset);
 243         if (*m != MAP_FAILED)
 244                 return 1;
 245 err:
 246         *m = NULL;
 247         return -ERRNO_TO_PARA_ERROR(errno);
 248 }
 249
 250 /**
 251  * Wrapper for the open(2) system call.
 252  *
 253  * \param path The filename.
 254  * \param flags The usual open(2) flags.
 255  * \param mode Specifies the permissions to use.
 256  *
 257  * The mode parameter must be specified when O_CREAT is in the flags, and is
 258  * ignored otherwise.
 259  *
 260  * \return The file descriptor on success, negative on errors.
 261  *
 262  * \sa open(2).
 263  */
 264 int para_open(const char *path, int flags, mode_t mode)
 265 {
 266         int ret = open(path, flags, mode);
 267
 268         if (ret >= 0)
 269                 return ret;
 270         return -ERRNO_TO_PARA_ERROR(errno);
 271 }
 272
 273 /**
 274  * Wrapper for chdir(2).
 275  *
 276  * \param path The specified directory.
 277  *
 278  * \return Standard.
 279  */
 280 int para_chdir(const char *path)
 281 {
 282         int ret = chdir(path);
 283
 284         if (ret >= 0)
 285                 return 1;
 286         return -ERRNO_TO_PARA_ERROR(errno);
 287 }
 288
 289 /**
 290  * Save the cwd and open a given directory.
 291  *
 292  * \param dirname Path to the directory to open.
 293  * \param dir Result pointer.
 294  * \param cwd File descriptor of the current working directory.
 295  *
 296  * \return Standard.
 297  *
 298  * Opening the current directory (".") and calling fchdir() to return is
 299  * usually faster and more reliable than saving cwd in some buffer and calling
 300  * chdir() afterwards.
 301  *
 302  * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
 303  * stored in \a cwd. If the function returns success, and \a cwd is not \p
 304  * NULL, the caller must close this file descriptor (probably after calling
 305  * fchdir(*cwd)).
 306  *
 307  * On errors, the function undos everything, so the caller needs neither close
 308  * any files, nor change back to the original working directory.
 309  *
 310  * \sa getcwd(3).
 311  *
 312  */
 313 int para_opendir(const char *dirname, DIR **dir, int *cwd)
 314 {
 315         int ret;
 316
 317         if (cwd) {
 318                 ret = para_open(".", O_RDONLY, 0);
 319                 if (ret < 0)
 320                         return ret;
 321                 *cwd = ret;
 322         }
 323         ret = para_chdir(dirname);
 324         if (ret < 0)
 325                 goto close_cwd;
 326         *dir = opendir(".");
 327         if (*dir)
 328                 return 1;
 329         ret = -ERRNO_TO_PARA_ERROR(errno);
 330         /* Ignore return value of fchdir() and close(). We're busted anyway. */
 331         if (cwd) {
 332                 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
 333         }
 334 close_cwd:
 335         if (cwd)
 336                 close(*cwd);
 337         return ret;
 338 }
 339
 340 /**
 341  * A wrapper for fchdir().
 342  *
 343  * \param fd An open file descriptor.
 344  *
 345  * \return Standard.
 346  */
 347 int para_fchdir(int fd)
 348 {
 349         if (fchdir(fd) < 0)
 350                 return -ERRNO_TO_PARA_ERROR(errno);
 351         return 1;
 352 }
 353
 354 /**
 355  * A wrapper for mkdir(2).
 356  *
 357  * \param path Name of the directory to create.
 358  * \param mode The permissions to use.
 359  *
 360  * \return Standard.
 361  */
 362 int para_mkdir(const char *path, mode_t mode)
 363 {
 364         if (!mkdir(path, mode))
 365                 return 1;
 366         return -ERRNO_TO_PARA_ERROR(errno);
 367 }
 368
 369 /**
 370  * Open a file and map it into memory.
 371  *
 372  * \param path Name of the regular file to map.
 373  * \param open_mode Either \p O_RDONLY or \p O_RDWR.
 374  * \param map On success, the mapping is returned here.
 375  * \param size size of the mapping.
 376  * \param fd_ptr The file descriptor of the mapping.
 377  *
 378  * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
 379  * open call is closed after mmap().  Otherwise the file is kept open and the
 380  * file descriptor is returned in \a fd_ptr.
 381  *
 382  * \return Standard.
 383  *
 384  * \sa para_open(), mmap(2).
 385  */
 386 int mmap_full_file(const char *path, int open_mode, void **map,
 387                 size_t *size, int *fd_ptr)
 388 {
 389         int fd, ret, mmap_prot, mmap_flags;
 390         struct stat file_status;
 391
 392         if (open_mode == O_RDONLY) {
 393                 mmap_prot = PROT_READ;
 394                 mmap_flags = MAP_PRIVATE;
 395         } else {
 396                 mmap_prot = PROT_READ | PROT_WRITE;
 397                 mmap_flags = MAP_SHARED;
 398         }
 399         ret = para_open(path, open_mode, 0);
 400         if (ret < 0)
 401                 return ret;
 402         fd = ret;
 403         if (fstat(fd, &file_status) < 0) {
 404                 ret = -ERRNO_TO_PARA_ERROR(errno);
 405                 goto out;
 406         }
 407         *size = file_status.st_size;
 408         ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
 409 out:
 410         if (ret < 0 || !fd_ptr)
 411                 close(fd);
 412         else
 413                 *fd_ptr = fd;
 414         return ret;
 415 }
 416
 417 /**
 418  * A wrapper for munmap(2).
 419  *
 420  * \param start The start address of the memory mapping.
 421  * \param length The size of the mapping.
 422  *
 423  * \return Standard.
 424  *
 425  * \sa munmap(2), mmap_full_file().
 426  */
 427 int para_munmap(void *start, size_t length)
 428 {
 429         int err;
 430         if (munmap(start, length) >= 0)
 431                 return 1;
 432         err = errno;
 433         PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
 434                 strerror(err));
 435         return -ERRNO_TO_PARA_ERROR(err);
 436 }
 437
 438 /**
 439  * Check a file descriptor for writability.
 440  *
 441  * \param fd The file descriptor.
 442  *
 443  * \return positive if fd is ready for writing, zero if it isn't, negative if
 444  * an error occurred.
 445  */
 446
 447 int write_ok(int fd)
 448 {
 449         struct timeval tv = {0, 0};
 450         fd_set wfds;
 451         int ret;
 452 again:
 453         FD_ZERO(&wfds);
 454         FD_SET(fd, &wfds);
 455         tv.tv_sec = 0;
 456         tv.tv_usec = 0;
 457         ret = select(fd + 1, NULL, &wfds, NULL, &tv);
 458         if (ret < 0 && errno == EINTR)
 459                 goto again;
 460         return ret;
 461 }
 462
 463 /**
 464  * Ensure that file descriptors 0, 1, and 2 are valid.
 465  *
 466  * Common approach that opens /dev/null until it gets a file descriptor greater
 467  * than two.
 468  *
 469  * \sa okir's Black Hats Manual.
 470  */
 471 void valid_fd_012(void)
 472 {
 473         while (1) {
 474                 int fd = open("/dev/null", O_RDWR);
 475                 if (fd < 0)
 476                         exit(EXIT_FAILURE);
 477                 if (fd > 2) {
 478                         close(fd);
 479                         break;
 480                 }
 481         }
 482 }