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
 178         if (fd < 0 || fd >= FD_SETSIZE) {
 179                 PARA_EMERG_LOG("fatal: tried to add invalid fd %d\n", fd);
 180                 exit(EXIT_FAILURE);
 181         }
 182 #if 0
 183         {
 184                 int flags = fcntl(fd, F_GETFL);
 185                 if (!(flags & O_NONBLOCK)) {
 186                         PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
 187                         exit(EXIT_FAILURE);
 188                 }
 189         }
 190 #endif
 191         FD_SET(fd, fds);
 192         *max_fileno = PARA_MAX(*max_fileno, fd);
 193 }
 194
 195 /**
 196  * Paraslash's wrapper for fgets(3).
 197  *
 198  * \param line Pointer to the buffer to store the line.
 199  * \param size The size of the buffer given by \a line.
 200  * \param f The stream to read from.
 201  *
 202  * \return Unlike the standard fgets() function, an integer value
 203  * is returned. On success, this function returns 1. On errors, -E_FGETS
 204  * is returned. A zero return value indicates an end of file condition.
 205  */
 206 __must_check int para_fgets(char *line, int size, FILE *f)
 207 {
 208 again:
 209         if (fgets(line, size, f))
 210                 return 1;
 211         if (feof(f))
 212                 return 0;
 213         if (!ferror(f))
 214                 return -E_FGETS;
 215         if (errno != EINTR) {
 216                 PARA_ERROR_LOG("%s\n", strerror(errno));
 217                 return -E_FGETS;
 218         }
 219         clearerr(f);
 220         goto again;
 221 }
 222
 223 /**
 224  * Paraslash's wrapper for mmap.
 225  *
 226  * \param length Number of bytes to mmap.
 227  * \param prot Either PROT_NONE or the bitwise OR of one or more of
 228  * PROT_EXEC PROT_READ PROT_WRITE.
 229  * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
 230  * \param fd The file to mmap from.
 231  * \param offset Mmap start.
 232  *
 233  * \return This function either returns a valid pointer to the mapped area
 234  * or calls exit() on errors.
 235  */
 236 void *para_mmap(size_t length, int prot, int flags, int fd, off_t offset)
 237 {
 238         void *ret = mmap(NULL, length, prot, flags, fd, offset);
 239         if (ret != MAP_FAILED)
 240                 return ret;
 241         PARA_EMERG_LOG("mmap failed: %s\n", strerror(errno));
 242         PARA_EMERG_LOG("length: %zu, flags: %d, fd: %d, offset: %zu\n",
 243                 length, flags, fd, (size_t)offset);
 244         exit(EXIT_FAILURE);
 245 }
 246
 247 /**
 248  * Wrapper for the open(2) system call.
 249  *
 250  * \param path The filename.
 251  * \param flags The usual open(2) flags.
 252  * \param mode Specifies the permissions to use.
 253  *
 254  * The mode parameter must be specified when O_CREAT is in the flags, and is
 255  * ignored otherwise.
 256  *
 257  * \return The file descriptor on success, negative on errors.
 258  *
 259  * \sa open(2).
 260  */
 261 int para_open(const char *path, int flags, mode_t mode)
 262 {
 263         int ret = open(path, flags, mode);
 264
 265         if (ret >= 0)
 266                 return ret;
 267         return -ERRNO_TO_PARA_ERROR(errno);
 268 }
 269
 270 /**
 271  * Wrapper for chdir(2).
 272  *
 273  * \param path The specified directory.
 274  *
 275  * \return Standard.
 276  */
 277 int para_chdir(const char *path)
 278 {
 279         int ret = chdir(path);
 280
 281         if (ret >= 0)
 282                 return 1;
 283         return -ERRNO_TO_PARA_ERROR(errno);
 284 }
 285
 286 /**
 287  * Save the cwd and open a given directory.
 288  *
 289  * \param dirname Path to the directory to open.
 290  * \param dir Result pointer.
 291  * \param cwd File descriptor of the current working directory.
 292  *
 293  * \return Standard.
 294  *
 295  * Opening the current directory (".") and calling fchdir() to return is
 296  * usually faster and more reliable than saving cwd in some buffer and calling
 297  * chdir() afterwards.
 298  *
 299  * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
 300  * stored in \a cwd. If the function returns success, and \a cwd is not \p
 301  * NULL, the caller must close this file descriptor (probably after calling
 302  * fchdir(*cwd)).
 303  *
 304  * On errors, the function undos everything, so the caller needs neither close
 305  * any files, nor change back to the original working directory.
 306  *
 307  * \sa getcwd(3).
 308  *
 309  */
 310 int para_opendir(const char *dirname, DIR **dir, int *cwd)
 311 {
 312         int ret;
 313
 314         if (cwd) {
 315                 ret = para_open(".", O_RDONLY, 0);
 316                 if (ret < 0)
 317                         return ret;
 318                 *cwd = ret;
 319         }
 320         ret = para_chdir(dirname);
 321         if (ret < 0)
 322                 goto close_cwd;
 323         *dir = opendir(".");
 324         if (*dir)
 325                 return 1;
 326         ret = -ERRNO_TO_PARA_ERROR(errno);
 327         /* Ignore return value of fchdir() and close(). We're busted anyway. */
 328         if (cwd) {
 329                 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
 330         }
 331 close_cwd:
 332         if (cwd)
 333                 close(*cwd);
 334         return ret;
 335 }
 336
 337 /**
 338  * A wrapper for fchdir().
 339  *
 340  * \param fd An open file descriptor.
 341  *
 342  * \return Standard.
 343  */
 344 int para_fchdir(int fd)
 345 {
 346         if (fchdir(fd) < 0)
 347                 return -ERRNO_TO_PARA_ERROR(errno);
 348         return 1;
 349 }
 350
 351 /**
 352  * A wrapper for mkdir(2).
 353  *
 354  * \param path Name of the directory to create.
 355  * \param mode The permissions to use.
 356  *
 357  * \return Standard.
 358  */
 359 int para_mkdir(const char *path, mode_t mode)
 360 {
 361         if (!mkdir(path, mode))
 362                 return 1;
 363         return -ERRNO_TO_PARA_ERROR(errno);
 364 }
 365
 366 /**
 367  * Open a file and map it into memory.
 368  *
 369  * \param path Name of the regular file to map.
 370  * \param open_mode Either \p O_RDONLY or \p O_RDWR.
 371  * \param map On success, the mapping is returned here.
 372  * \param size size of the mapping.
 373  * \param fd_ptr The file descriptor of the mapping.
 374  *
 375  * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
 376  * open call is closed after mmap().  Otherwise the file is kept open and the
 377  * file descriptor is returned in \a fd_ptr.
 378  *
 379  * \return Standard.
 380  *
 381  * \sa para_open(), mmap(2).
 382  */
 383 int mmap_full_file(const char *path, int open_mode, void **map,
 384                 size_t *size, int *fd_ptr)
 385 {
 386         int fd, ret, mmap_prot, mmap_flags;
 387         struct stat file_status;
 388
 389         if (open_mode == O_RDONLY) {
 390                 mmap_prot = PROT_READ;
 391                 mmap_flags = MAP_PRIVATE;
 392         } else {
 393                 mmap_prot = PROT_READ | PROT_WRITE;
 394                 mmap_flags = MAP_SHARED;
 395         }
 396         ret = para_open(path, open_mode, 0);
 397         if (ret < 0)
 398                 return ret;
 399         fd = ret;
 400         if (fstat(fd, &file_status) < 0) {
 401                 ret = -ERRNO_TO_PARA_ERROR(errno);
 402                 goto out;
 403         }
 404         *size = file_status.st_size;
 405         ret = -E_EMPTY;
 406         PARA_DEBUG_LOG("%s: size %zu\n", path, *size);
 407         if (!*size)
 408                 goto out;
 409         *map = mmap(NULL, *size, mmap_prot, mmap_flags, fd, 0);
 410         if (*map == MAP_FAILED) {
 411                 *map = NULL;
 412                 ret = -E_MMAP;
 413                 goto out;
 414         }
 415         ret = 1;
 416 out:
 417         if (ret < 0 || !fd_ptr)
 418                 close(fd);
 419         else
 420                 *fd_ptr = fd;
 421         return ret;
 422 }
 423
 424 /**
 425  * A wrapper for munmap(2).
 426  *
 427  * \param start The start address of the memory mapping.
 428  * \param length The size of the mapping.
 429  *
 430  * \return Positive on success, \p -E_MUNMAP on errors.
 431  *
 432  * \sa munmap(2), mmap_full_file().
 433  */
 434 int para_munmap(void *start, size_t length)
 435 {
 436         int err;
 437         if (munmap(start, length) >= 0)
 438                 return 1;
 439         err = errno;
 440         PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
 441                 strerror(err));
 442         return -ERRNO_TO_PARA_ERROR(err);
 443 }
 444
 445 /**
 446  * Check a file descriptor for writability.
 447  *
 448  * \param fd The file descriptor.
 449  *
 450  * \return positive if fd is ready for writing, zero if it isn't, negative if
 451  * an error occurred.
 452  */
 453
 454 int write_ok(int fd)
 455 {
 456         struct timeval tv = {0, 0};
 457         fd_set wfds;
 458         int ret;
 459 again:
 460         FD_ZERO(&wfds);
 461         FD_SET(fd, &wfds);
 462         tv.tv_sec = 0;
 463         tv.tv_usec = 0;
 464         ret = select(fd + 1, NULL, &wfds, NULL, &tv);
 465         if (ret < 0 && errno == EINTR)
 466                 goto again;
 467         return ret;
 468 }
 469
 470 /**
 471  * Ensure that file descriptors 0, 1, and 2 are valid.
 472  *
 473  * Common approach that opens /dev/null until it gets a file descriptor greater
 474  * than two.
 475  *
 476  * \sa okir's Black Hats Manual.
 477  */
 478 void valid_fd_012(void)
 479 {
 480         while (1) {
 481                 int fd = open("/dev/null", O_RDWR);
 482                 if (fd < 0)
 483                         exit(EXIT_FAILURE);
 484                 if (fd > 2) {
 485                         close(fd);
 486                         break;
 487                 }
 488         }
 489 }