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 non-blocking mode.
  65  *
  66  * \param fd The file descriptor.
  67  *
  68  * \return Standard.
  69  */
  70 int mark_fd_nonblock(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 in a fd_set.
  83  *
  84  * \param fd The file descriptor to be set.
  85  * \param fds The file descriptor set.
  86  * \param max_fileno Highest-numbered file descriptor.
  87  *
  88  * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
  89  * return, \a max_fileno contains the maximum of the old_value and \a fd.
  90  *
  91  * \sa para_select.
  92 */
  93 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
  94 {
  95
  96         if (fd < 0 || fd >= FD_SETSIZE) {
  97                 PARA_EMERG_LOG("fatal: tried to add invalid fd %d\n", fd);
  98                 exit(EXIT_FAILURE);
  99         }
 100 #if 0
 101         {
 102                 int flags = fcntl(fd, F_GETFL);
 103                 if (!(flags & O_NONBLOCK)) {
 104                         PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
 105                         exit(EXIT_FAILURE);
 106                 }
 107         }
 108 #endif
 109         FD_SET(fd, fds);
 110         *max_fileno = PARA_MAX(*max_fileno, fd);
 111 }
 112
 113 /**
 114 * Paraslash's wrapper for fgets(3).
 115
 116 * \param line Pointer to the buffer to store the line.
 117 * \param size The size of the buffer given by \a line.
 118 * \param f The stream to read from.
 119 *
 120 * \return Unlike the standard fgets() function, an integer value
 121 * is returned. On success, this function returns 1. On errors, -E_FGETS
 122 * is returned. A zero return value indicates an end of file condition.
 123 */
 124 __must_check int para_fgets(char *line, int size, FILE *f)
 125 {
 126 again:
 127         if (fgets(line, size, f))
 128                 return 1;
 129         if (feof(f))
 130                 return 0;
 131         if (!ferror(f))
 132                 return -E_FGETS;
 133         if (errno != EINTR) {
 134                 PARA_ERROR_LOG("%s\n", strerror(errno));
 135                 return -E_FGETS;
 136         }
 137         clearerr(f);
 138         goto again;
 139 }
 140
 141 /**
 142  * Paraslash's wrapper for mmap.
 143  *
 144  * \param length Number of bytes to mmap.
 145  * \param prot Either PROT_NONE or the bitwise OR of one or more of
 146  * PROT_EXEC PROT_READ PROT_WRITE.
 147  * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
 148  * \param fd The file to mmap from.
 149  * \param offset Mmap start.
 150  *
 151  * \return This function either returns a valid pointer to the mapped area
 152  * or calls exit() on errors.
 153  */
 154 void *para_mmap(size_t length, int prot, int flags, int fd, off_t offset)
 155 {
 156         void *ret = mmap(NULL, length, prot, flags, fd, offset);
 157         if (ret != MAP_FAILED)
 158                 return ret;
 159         PARA_EMERG_LOG("mmap failed: %s\n", strerror(errno));
 160         PARA_EMERG_LOG("length: %zu, flags: %d, fd: %d, offset: %zu\n",
 161                 length, flags, fd, (size_t)offset);
 162         exit(EXIT_FAILURE);
 163 }
 164
 165 /**
 166  * Wrapper for the open(2) system call.
 167  *
 168  * \param path The filename.
 169  * \param flags The usual open(2) flags.
 170  * \param mode Specifies the permissions to use.
 171  *
 172  * The mode parameter must be specified when O_CREAT is in the flags, and is
 173  * ignored otherwise.
 174  *
 175  * \return The file descriptor on success, negative on errors.
 176  *
 177  * \sa open(2).
 178  */
 179 int para_open(const char *path, int flags, mode_t mode)
 180 {
 181         int ret = open(path, flags, mode);
 182
 183         if (ret >= 0)
 184                 return ret;
 185         return -ERRNO_TO_PARA_ERROR(errno);
 186 }
 187
 188 /**
 189  * Wrapper for chdir(2).
 190  *
 191  * \param path The specified directory.
 192  *
 193  * \return Standard.
 194  */
 195 int para_chdir(const char *path)
 196 {
 197         int ret = chdir(path);
 198
 199         if (ret >= 0)
 200                 return 1;
 201         return -ERRNO_TO_PARA_ERROR(errno);
 202 }
 203
 204 /**
 205  * Save the cwd and open a given directory.
 206  *
 207  * \param dirname Path to the directory to open.
 208  * \param dir Result pointer.
 209  * \param cwd File descriptor of the current working directory.
 210  *
 211  * \return Standard.
 212  *
 213  * Opening the current directory (".") and calling fchdir() to return is
 214  * usually faster and more reliable than saving cwd in some buffer and calling
 215  * chdir() afterwards.
 216  *
 217  * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
 218  * stored in \a cwd. If the function returns success, and \a cwd is not \p
 219  * NULL, the caller must close this file descriptor (probably after calling
 220  * fchdir(*cwd)).
 221  *
 222  * On errors, the function undos everything, so the caller needs neither close
 223  * any files, nor change back to the original working directory.
 224  *
 225  * \sa getcwd(3).
 226  *
 227  */
 228 int para_opendir(const char *dirname, DIR **dir, int *cwd)
 229 {
 230         int ret;
 231
 232         if (cwd) {
 233                 ret = para_open(".", O_RDONLY, 0);
 234                 if (ret < 0)
 235                         return ret;
 236                 *cwd = ret;
 237         }
 238         ret = para_chdir(dirname);
 239         if (ret < 0)
 240                 goto close_cwd;
 241         *dir = opendir(".");
 242         if (*dir)
 243                 return 1;
 244         ret = -ERRNO_TO_PARA_ERROR(errno);
 245 /* Ignore return value of fchdir() and close(). We're busted anyway. */
 246         if (cwd)
 247                 fchdir(*cwd);
 248 close_cwd:
 249         if (cwd)
 250                 close(*cwd);
 251         return ret;
 252 }
 253
 254 /**
 255  * A wrapper for fchdir().
 256  *
 257  * \param fd An open file descriptor.
 258  *
 259  * \return Standard.
 260  */
 261 int para_fchdir(int fd)
 262 {
 263         if (fchdir(fd) < 0)
 264                 return -ERRNO_TO_PARA_ERROR(errno);
 265         return 1;
 266 }
 267
 268 /**
 269  * A wrapper for mkdir(2).
 270  *
 271  * \param path Name of the directory to create.
 272  * \param mode The permissions to use.
 273  *
 274  * \return Standard.
 275  */
 276 int para_mkdir(const char *path, mode_t mode)
 277 {
 278         if (!mkdir(path, mode))
 279                 return 1;
 280         return -ERRNO_TO_PARA_ERROR(errno);
 281 }