fd.c

   1 /*
   2  * Copyright (C) 2006-2007 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  * Check whether a file exists.
  20  *
  21  * \param fn The file name.
  22  *
  23  * \return Non-zero iff file exists.
  24  */
  25 int file_exists(const char *fn)
  26 {
  27         struct stat statbuf;
  28
  29         return !stat(fn, &statbuf);
  30 }
  31
  32 /**
  33  * Paraslash's wrapper for select(2).
  34  *
  35  * It calls select(2) (with no exceptfds) and starts over if select() was
  36  * interrupted by a signal.
  37  *
  38  * \param n The highest-numbered descriptor in any of the two sets, plus 1.
  39  * \param readfds fds that should be checked for readability.
  40  * \param writefds fds that should be checked for writablility.
  41  * \param timeout_tv upper bound on the amount of time elapsed before select()
  42  * returns.
  43  *
  44  * \return The return value of the underlying select() call on success, the
  45  * negative system error code on errors.
  46  *
  47  * All arguments are passed verbatim to select(2).
  48  * \sa select(2) select_tut(2).
  49  */
  50 int para_select(int n, fd_set *readfds, fd_set *writefds,
  51                 struct timeval *timeout_tv)
  52 {
  53         int ret, err;
  54         do {
  55                 ret = select(n, readfds, writefds, NULL, timeout_tv);
  56                 err = errno;
  57         } while (ret < 0 && err == EINTR);
  58         if (ret < 0)
  59                 return -ERRNO_TO_PARA_ERROR(errno);
  60         return ret;
  61 }
  62
  63 /**
  64  * Set a file descriptor to blocking mode.
  65  *
  66  * \param fd The file descriptor.
  67  *
  68  * \return Standard.
  69  */
  70 int mark_fd_blocking(int fd)
  71 {
  72         int flags = fcntl(fd, F_GETFL);
  73         if (flags < 0)
  74                 return -ERRNO_TO_PARA_ERROR(errno);
  75         flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
  76         if (flags < 0)
  77                 return -ERRNO_TO_PARA_ERROR(errno);
  78         return 1;
  79 }
  80
  81 /**
  82  * Set a file descriptor to non-blocking mode.
  83  *
  84  * \param fd The file descriptor.
  85  *
  86  * \return Standard.
  87  */
  88 int mark_fd_nonblocking(int fd)
  89 {
  90         int flags = fcntl(fd, F_GETFL);
  91         if (flags < 0)
  92                 return -ERRNO_TO_PARA_ERROR(errno);
  93         flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
  94         if (flags < 0)
  95                 return -ERRNO_TO_PARA_ERROR(errno);
  96         return 1;
  97 }
  98
  99 /**
 100  * Set a file descriptor in a fd_set.
 101  *
 102  * \param fd The file descriptor to be set.
 103  * \param fds The file descriptor set.
 104  * \param max_fileno Highest-numbered file descriptor.
 105  *
 106  * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
 107  * return, \a max_fileno contains the maximum of the old_value and \a fd.
 108  *
 109  * \sa para_select.
 110 */
 111 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
 112 {
 113
 114         if (fd < 0 || fd >= FD_SETSIZE) {
 115                 PARA_EMERG_LOG("fatal: tried to add invalid fd %d\n", fd);
 116                 exit(EXIT_FAILURE);
 117         }
 118 #if 0
 119         {
 120                 int flags = fcntl(fd, F_GETFL);
 121                 if (!(flags & O_NONBLOCK)) {
 122                         PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
 123                         exit(EXIT_FAILURE);
 124                 }
 125         }
 126 #endif
 127         FD_SET(fd, fds);
 128         *max_fileno = PARA_MAX(*max_fileno, fd);
 129 }
 130
 131 /**
 132 * Paraslash's wrapper for fgets(3).
 133
 134 * \param line Pointer to the buffer to store the line.
 135 * \param size The size of the buffer given by \a line.
 136 * \param f The stream to read from.
 137 *
 138 * \return Unlike the standard fgets() function, an integer value
 139 * is returned. On success, this function returns 1. On errors, -E_FGETS
 140 * is returned. A zero return value indicates an end of file condition.
 141 */
 142 __must_check int para_fgets(char *line, int size, FILE *f)
 143 {
 144 again:
 145         if (fgets(line, size, f))
 146                 return 1;
 147         if (feof(f))
 148                 return 0;
 149         if (!ferror(f))
 150                 return -E_FGETS;
 151         if (errno != EINTR) {
 152                 PARA_ERROR_LOG("%s\n", strerror(errno));
 153                 return -E_FGETS;
 154         }
 155         clearerr(f);
 156         goto again;
 157 }
 158
 159 /**
 160  * Paraslash's wrapper for mmap.
 161  *
 162  * \param length Number of bytes to mmap.
 163  * \param prot Either PROT_NONE or the bitwise OR of one or more of
 164  * PROT_EXEC PROT_READ PROT_WRITE.
 165  * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
 166  * \param fd The file to mmap from.
 167  * \param offset Mmap start.
 168  *
 169  * \return This function either returns a valid pointer to the mapped area
 170  * or calls exit() on errors.
 171  */
 172 void *para_mmap(size_t length, int prot, int flags, int fd, off_t offset)
 173 {
 174         void *ret = mmap(NULL, length, prot, flags, fd, offset);
 175         if (ret != MAP_FAILED)
 176                 return ret;
 177         PARA_EMERG_LOG("mmap failed: %s\n", strerror(errno));
 178         PARA_EMERG_LOG("length: %zu, flags: %d, fd: %d, offset: %zu\n",
 179                 length, flags, fd, (size_t)offset);
 180         exit(EXIT_FAILURE);
 181 }
 182
 183 /**
 184  * Wrapper for the open(2) system call.
 185  *
 186  * \param path The filename.
 187  * \param flags The usual open(2) flags.
 188  * \param mode Specifies the permissions to use.
 189  *
 190  * The mode parameter must be specified when O_CREAT is in the flags, and is
 191  * ignored otherwise.
 192  *
 193  * \return The file descriptor on success, negative on errors.
 194  *
 195  * \sa open(2).
 196  */
 197 int para_open(const char *path, int flags, mode_t mode)
 198 {
 199         int ret = open(path, flags, mode);
 200
 201         if (ret >= 0)
 202                 return ret;
 203         return -ERRNO_TO_PARA_ERROR(errno);
 204 }
 205
 206 /**
 207  * Wrapper for chdir(2).
 208  *
 209  * \param path The specified directory.
 210  *
 211  * \return Standard.
 212  */
 213 int para_chdir(const char *path)
 214 {
 215         int ret = chdir(path);
 216
 217         if (ret >= 0)
 218                 return 1;
 219         return -ERRNO_TO_PARA_ERROR(errno);
 220 }
 221
 222 /**
 223  * Save the cwd and open a given directory.
 224  *
 225  * \param dirname Path to the directory to open.
 226  * \param dir Result pointer.
 227  * \param cwd File descriptor of the current working directory.
 228  *
 229  * \return Standard.
 230  *
 231  * Opening the current directory (".") and calling fchdir() to return is
 232  * usually faster and more reliable than saving cwd in some buffer and calling
 233  * chdir() afterwards.
 234  *
 235  * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
 236  * stored in \a cwd. If the function returns success, and \a cwd is not \p
 237  * NULL, the caller must close this file descriptor (probably after calling
 238  * fchdir(*cwd)).
 239  *
 240  * On errors, the function undos everything, so the caller needs neither close
 241  * any files, nor change back to the original working directory.
 242  *
 243  * \sa getcwd(3).
 244  *
 245  */
 246 int para_opendir(const char *dirname, DIR **dir, int *cwd)
 247 {
 248         int ret;
 249
 250         if (cwd) {
 251                 ret = para_open(".", O_RDONLY, 0);
 252                 if (ret < 0)
 253                         return ret;
 254                 *cwd = ret;
 255         }
 256         ret = para_chdir(dirname);
 257         if (ret < 0)
 258                 goto close_cwd;
 259         *dir = opendir(".");
 260         if (*dir)
 261                 return 1;
 262         ret = -ERRNO_TO_PARA_ERROR(errno);
 263 /* Ignore return value of fchdir() and close(). We're busted anyway. */
 264         if (cwd)
 265                 fchdir(*cwd);
 266 close_cwd:
 267         if (cwd)
 268                 close(*cwd);
 269         return ret;
 270 }
 271
 272 /**
 273  * A wrapper for fchdir().
 274  *
 275  * \param fd An open file descriptor.
 276  *
 277  * \return Standard.
 278  */
 279 int para_fchdir(int fd)
 280 {
 281         if (fchdir(fd) < 0)
 282                 return -ERRNO_TO_PARA_ERROR(errno);
 283         return 1;
 284 }
 285
 286 /**
 287  * A wrapper for mkdir(2).
 288  *
 289  * \param path Name of the directory to create.
 290  * \param mode The permissions to use.
 291  *
 292  * \return Standard.
 293  */
 294 int para_mkdir(const char *path, mode_t mode)
 295 {
 296         if (!mkdir(path, mode))
 297                 return 1;
 298         return -ERRNO_TO_PARA_ERROR(errno);
 299 }
 300
 301 /**
 302  * Open a file and map it into memory.
 303  *
 304  * \param path Name of the regular file to map.
 305  * \param open_mode Either \p O_RDONLY or \p O_RDWR.
 306  * \param map On success, the mapping is returned here.
 307  * \param size size of the mapping.
 308  * \param fd_ptr The file descriptor of the mapping.
 309  *
 310  * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
 311  * open call is closed after mmap().  Otherwise the file is kept open and the
 312  * file descriptor is returned in \a fd_ptr.
 313  *
 314  * \return Standard.
 315  *
 316  * \sa para_open(), mmap(2).
 317  */
 318 int mmap_full_file(const char *path, int open_mode, void **map,
 319                 size_t *size, int *fd_ptr)
 320 {
 321         int fd, ret, mmap_prot, mmap_flags;
 322         struct stat file_status;
 323
 324         if (open_mode == O_RDONLY) {
 325                 mmap_prot = PROT_READ;
 326                 mmap_flags = MAP_PRIVATE;
 327         } else {
 328                 mmap_prot = PROT_READ | PROT_WRITE;
 329                 mmap_flags = MAP_SHARED;
 330         }
 331         ret = para_open(path, open_mode, 0);
 332         if (ret < 0)
 333                 return ret;
 334         fd = ret;
 335         if (fstat(fd, &file_status) < 0) {
 336                 ret = -ERRNO_TO_PARA_ERROR(errno);
 337                 goto out;
 338         }
 339         *size = file_status.st_size;
 340         ret = -E_EMPTY;
 341         PARA_DEBUG_LOG("%s: size %zu\n", path, *size);
 342         if (!*size)
 343                 goto out;
 344         *map = mmap(NULL, *size, mmap_prot, mmap_flags, fd, 0);
 345         if (*map == MAP_FAILED) {
 346                 *map = NULL;
 347                 ret = -E_MMAP;
 348                 goto out;
 349         }
 350         ret = 1;
 351 out:
 352         if (ret < 0 || !fd_ptr)
 353                 close(fd);
 354         else
 355                 *fd_ptr = fd;
 356         return ret;
 357 }
 358
 359 /**
 360  * A wrapper for munmap(2).
 361  *
 362  * \param start The start address of the memory mapping.
 363  * \param length The size of the mapping.
 364  *
 365  * \return Positive on success, \p -E_MUNMAP on errors.
 366  *
 367  * \sa munmap(2), mmap_full_file().
 368  */
 369 int para_munmap(void *start, size_t length)
 370 {
 371         if (munmap(start, length) >= 0)
 372                 return 1;
 373         PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
 374                 strerror(errno));
 375         return -E_MUNMAP;
 376 }
 377
 378 /**
 379  * check a file descriptor for writability
 380  *
 381  * \param fd the file descriptor
 382  *
 383  * \return positive if fd is ready for writing, zero if it isn't, negative if
 384  * an error occurred.
 385  */
 386
 387 int write_ok(int fd)
 388 {
 389         struct timeval tv = {0, 0};
 390         fd_set wfds;
 391         int ret;
 392 again:
 393         FD_ZERO(&wfds);
 394         FD_SET(fd, &wfds);
 395         tv.tv_sec = 0;
 396         tv.tv_usec = 0;
 397         ret = select(fd + 1, NULL, &wfds, NULL, &tv);
 398         if (ret < 0 && errno == EINTR)
 399                 goto again;
 400         return ret;
 401 }