Documentation updates for 0.4.
[paraslash.git] / 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 #include "string.h"
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 Positive on success, \p -E_MUNMAP on errors.
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 }
483
484 /**
485 * Traverse the given directory recursively.
486 *
487 * \param dirname The directory to traverse.
488 * \param func The function to call for each entry.
489 * \param private_data Pointer to an arbitrary data structure.
490 *
491 * For each regular file under \a dirname, the supplied function \a func is
492 * called. The full path of the regular file and the \a private_data pointer
493 * are passed to \a func. Directories for which the calling process has no
494 * permissions to change to are silently ignored.
495 *
496 * \return Standard.
497 */
498 int for_each_file_in_dir(const char *dirname,
499 int (*func)(const char *, void *), void *private_data)
500 {
501 DIR *dir;
502 struct dirent *entry;
503 int cwd_fd, ret2, ret = para_opendir(dirname, &dir, &cwd_fd);
504
505 if (ret < 0)
506 return ret == -ERRNO_TO_PARA_ERROR(EACCES)? 1 : ret;
507 /* scan cwd recursively */
508 while ((entry = readdir(dir))) {
509 mode_t m;
510 char *tmp;
511 struct stat s;
512
513 if (!strcmp(entry->d_name, "."))
514 continue;
515 if (!strcmp(entry->d_name, ".."))
516 continue;
517 if (lstat(entry->d_name, &s) == -1)
518 continue;
519 m = s.st_mode;
520 if (!S_ISREG(m) && !S_ISDIR(m))
521 continue;
522 tmp = make_message("%s/%s", dirname, entry->d_name);
523 if (!S_ISDIR(m)) {
524 ret = func(tmp, private_data);
525 free(tmp);
526 if (ret < 0)
527 goto out;
528 continue;
529 }
530 /* directory */
531 ret = for_each_file_in_dir(tmp, func, private_data);
532 free(tmp);
533 if (ret < 0)
534 goto out;
535 }
536 ret = 1;
537 out:
538 closedir(dir);
539 ret2 = para_fchdir(cwd_fd);
540 if (ret2 < 0 && ret >= 0)
541 ret = ret2;
542 close(cwd_fd);
543 return ret;
544 }