fd.c: Simplify write_ok().
[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;
118 do
119 ret = select(n, readfds, writefds, NULL, timeout_tv);
120 while (ret < 0 && errno == EINTR);
121 if (ret < 0)
122 return -ERRNO_TO_PARA_ERROR(errno);
123 return ret;
124 }
125
126 /**
127 * Set a file descriptor to blocking mode.
128 *
129 * \param fd The file descriptor.
130 *
131 * \return Standard.
132 */
133 __must_check int mark_fd_blocking(int fd)
134 {
135 int flags = fcntl(fd, F_GETFL);
136 if (flags < 0)
137 return -ERRNO_TO_PARA_ERROR(errno);
138 flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
139 if (flags < 0)
140 return -ERRNO_TO_PARA_ERROR(errno);
141 return 1;
142 }
143
144 /**
145 * Set a file descriptor to non-blocking mode.
146 *
147 * \param fd The file descriptor.
148 *
149 * \return Standard.
150 */
151 __must_check int mark_fd_nonblocking(int fd)
152 {
153 int flags = fcntl(fd, F_GETFL);
154 if (flags < 0)
155 return -ERRNO_TO_PARA_ERROR(errno);
156 flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
157 if (flags < 0)
158 return -ERRNO_TO_PARA_ERROR(errno);
159 return 1;
160 }
161
162 /**
163 * Set a file descriptor in a fd_set.
164 *
165 * \param fd The file descriptor to be set.
166 * \param fds The file descriptor set.
167 * \param max_fileno Highest-numbered file descriptor.
168 *
169 * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
170 * return, \a max_fileno contains the maximum of the old_value and \a fd.
171 *
172 * \sa para_select.
173 */
174 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
175 {
176 assert(fd >= 0 && fd < FD_SETSIZE);
177 #if 0
178 {
179 int flags = fcntl(fd, F_GETFL);
180 if (!(flags & O_NONBLOCK)) {
181 PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
182 exit(EXIT_FAILURE);
183 }
184 }
185 #endif
186 FD_SET(fd, fds);
187 *max_fileno = PARA_MAX(*max_fileno, fd);
188 }
189
190 /**
191 * Paraslash's wrapper for fgets(3).
192 *
193 * \param line Pointer to the buffer to store the line.
194 * \param size The size of the buffer given by \a line.
195 * \param f The stream to read from.
196 *
197 * \return Unlike the standard fgets() function, an integer value
198 * is returned. On success, this function returns 1. On errors, -E_FGETS
199 * is returned. A zero return value indicates an end of file condition.
200 */
201 __must_check int para_fgets(char *line, int size, FILE *f)
202 {
203 again:
204 if (fgets(line, size, f))
205 return 1;
206 if (feof(f))
207 return 0;
208 if (!ferror(f))
209 return -E_FGETS;
210 if (errno != EINTR) {
211 PARA_ERROR_LOG("%s\n", strerror(errno));
212 return -E_FGETS;
213 }
214 clearerr(f);
215 goto again;
216 }
217
218 /**
219 * Paraslash's wrapper for mmap.
220 *
221 * \param length Number of bytes to mmap.
222 * \param prot Either PROT_NONE or the bitwise OR of one or more of
223 * PROT_EXEC PROT_READ PROT_WRITE.
224 * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
225 * \param fd The file to mmap from.
226 * \param offset Mmap start.
227 * \param map Result pointer.
228 *
229 * \return Standard.
230 *
231 * \sa mmap(2).
232 */
233 int para_mmap(size_t length, int prot, int flags, int fd, off_t offset,
234 void *map)
235 {
236 void **m = map;
237
238 errno = EINVAL;
239 if (!length)
240 goto err;
241 *m = mmap(NULL, length, prot, flags, fd, offset);
242 if (*m != MAP_FAILED)
243 return 1;
244 err:
245 *m = NULL;
246 return -ERRNO_TO_PARA_ERROR(errno);
247 }
248
249 /**
250 * Wrapper for the open(2) system call.
251 *
252 * \param path The filename.
253 * \param flags The usual open(2) flags.
254 * \param mode Specifies the permissions to use.
255 *
256 * The mode parameter must be specified when O_CREAT is in the flags, and is
257 * ignored otherwise.
258 *
259 * \return The file descriptor on success, negative on errors.
260 *
261 * \sa open(2).
262 */
263 int para_open(const char *path, int flags, mode_t mode)
264 {
265 int ret = open(path, flags, mode);
266
267 if (ret >= 0)
268 return ret;
269 return -ERRNO_TO_PARA_ERROR(errno);
270 }
271
272 /**
273 * Wrapper for chdir(2).
274 *
275 * \param path The specified directory.
276 *
277 * \return Standard.
278 */
279 int para_chdir(const char *path)
280 {
281 int ret = chdir(path);
282
283 if (ret >= 0)
284 return 1;
285 return -ERRNO_TO_PARA_ERROR(errno);
286 }
287
288 /**
289 * Save the cwd and open a given directory.
290 *
291 * \param dirname Path to the directory to open.
292 * \param dir Result pointer.
293 * \param cwd File descriptor of the current working directory.
294 *
295 * \return Standard.
296 *
297 * Opening the current directory (".") and calling fchdir() to return is
298 * usually faster and more reliable than saving cwd in some buffer and calling
299 * chdir() afterwards.
300 *
301 * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
302 * stored in \a cwd. If the function returns success, and \a cwd is not \p
303 * NULL, the caller must close this file descriptor (probably after calling
304 * fchdir(*cwd)).
305 *
306 * On errors, the function undos everything, so the caller needs neither close
307 * any files, nor change back to the original working directory.
308 *
309 * \sa getcwd(3).
310 *
311 */
312 int para_opendir(const char *dirname, DIR **dir, int *cwd)
313 {
314 int ret;
315
316 if (cwd) {
317 ret = para_open(".", O_RDONLY, 0);
318 if (ret < 0)
319 return ret;
320 *cwd = ret;
321 }
322 ret = para_chdir(dirname);
323 if (ret < 0)
324 goto close_cwd;
325 *dir = opendir(".");
326 if (*dir)
327 return 1;
328 ret = -ERRNO_TO_PARA_ERROR(errno);
329 /* Ignore return value of fchdir() and close(). We're busted anyway. */
330 if (cwd) {
331 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
332 }
333 close_cwd:
334 if (cwd)
335 close(*cwd);
336 return ret;
337 }
338
339 /**
340 * A wrapper for fchdir().
341 *
342 * \param fd An open file descriptor.
343 *
344 * \return Standard.
345 */
346 int para_fchdir(int fd)
347 {
348 if (fchdir(fd) < 0)
349 return -ERRNO_TO_PARA_ERROR(errno);
350 return 1;
351 }
352
353 /**
354 * A wrapper for mkdir(2).
355 *
356 * \param path Name of the directory to create.
357 * \param mode The permissions to use.
358 *
359 * \return Standard.
360 */
361 int para_mkdir(const char *path, mode_t mode)
362 {
363 if (!mkdir(path, mode))
364 return 1;
365 return -ERRNO_TO_PARA_ERROR(errno);
366 }
367
368 /**
369 * Open a file and map it into memory.
370 *
371 * \param path Name of the regular file to map.
372 * \param open_mode Either \p O_RDONLY or \p O_RDWR.
373 * \param map On success, the mapping is returned here.
374 * \param size size of the mapping.
375 * \param fd_ptr The file descriptor of the mapping.
376 *
377 * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
378 * open call is closed after mmap(). Otherwise the file is kept open and the
379 * file descriptor is returned in \a fd_ptr.
380 *
381 * \return Standard.
382 *
383 * \sa para_open(), mmap(2).
384 */
385 int mmap_full_file(const char *path, int open_mode, void **map,
386 size_t *size, int *fd_ptr)
387 {
388 int fd, ret, mmap_prot, mmap_flags;
389 struct stat file_status;
390
391 if (open_mode == O_RDONLY) {
392 mmap_prot = PROT_READ;
393 mmap_flags = MAP_PRIVATE;
394 } else {
395 mmap_prot = PROT_READ | PROT_WRITE;
396 mmap_flags = MAP_SHARED;
397 }
398 ret = para_open(path, open_mode, 0);
399 if (ret < 0)
400 return ret;
401 fd = ret;
402 if (fstat(fd, &file_status) < 0) {
403 ret = -ERRNO_TO_PARA_ERROR(errno);
404 goto out;
405 }
406 *size = file_status.st_size;
407 ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
408 out:
409 if (ret < 0 || !fd_ptr)
410 close(fd);
411 else
412 *fd_ptr = fd;
413 return ret;
414 }
415
416 /**
417 * A wrapper for munmap(2).
418 *
419 * \param start The start address of the memory mapping.
420 * \param length The size of the mapping.
421 *
422 * \return Positive on success, \p -E_MUNMAP on errors.
423 *
424 * \sa munmap(2), mmap_full_file().
425 */
426 int para_munmap(void *start, size_t length)
427 {
428 int err;
429 if (munmap(start, length) >= 0)
430 return 1;
431 err = errno;
432 PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
433 strerror(err));
434 return -ERRNO_TO_PARA_ERROR(err);
435 }
436
437 /**
438 * Check a file descriptor for writability.
439 *
440 * \param fd The file descriptor.
441 *
442 * \return positive if fd is ready for writing, zero if it isn't, negative if
443 * an error occurred.
444 */
445
446 int write_ok(int fd)
447 {
448 struct timeval tv;
449 fd_set wfds;
450
451 FD_ZERO(&wfds);
452 FD_SET(fd, &wfds);
453 tv.tv_sec = 0;
454 tv.tv_usec = 0;
455 return para_select(fd + 1, NULL, &wfds, &tv);
456 }
457
458 /**
459 * Ensure that file descriptors 0, 1, and 2 are valid.
460 *
461 * Common approach that opens /dev/null until it gets a file descriptor greater
462 * than two.
463 *
464 * \sa okir's Black Hats Manual.
465 */
466 void valid_fd_012(void)
467 {
468 while (1) {
469 int fd = open("/dev/null", O_RDWR);
470 if (fd < 0)
471 exit(EXIT_FAILURE);
472 if (fd > 2) {
473 close(fd);
474 break;
475 }
476 }
477 }
478
479 /**
480 * Traverse the given directory recursively.
481 *
482 * \param dirname The directory to traverse.
483 * \param func The function to call for each entry.
484 * \param private_data Pointer to an arbitrary data structure.
485 *
486 * For each regular file under \a dirname, the supplied function \a func is
487 * called. The full path of the regular file and the \a private_data pointer
488 * are passed to \a func. Directories for which the calling process has no
489 * permissions to change to are silently ignored.
490 *
491 * \return Standard.
492 */
493 int for_each_file_in_dir(const char *dirname,
494 int (*func)(const char *, void *), void *private_data)
495 {
496 DIR *dir;
497 struct dirent *entry;
498 int cwd_fd, ret2, ret = para_opendir(dirname, &dir, &cwd_fd);
499
500 if (ret < 0)
501 return ret == -ERRNO_TO_PARA_ERROR(EACCES)? 1 : ret;
502 /* scan cwd recursively */
503 while ((entry = readdir(dir))) {
504 mode_t m;
505 char *tmp;
506 struct stat s;
507
508 if (!strcmp(entry->d_name, "."))
509 continue;
510 if (!strcmp(entry->d_name, ".."))
511 continue;
512 if (lstat(entry->d_name, &s) == -1)
513 continue;
514 m = s.st_mode;
515 if (!S_ISREG(m) && !S_ISDIR(m))
516 continue;
517 tmp = make_message("%s/%s", dirname, entry->d_name);
518 if (!S_ISDIR(m)) {
519 ret = func(tmp, private_data);
520 free(tmp);
521 if (ret < 0)
522 goto out;
523 continue;
524 }
525 /* directory */
526 ret = for_each_file_in_dir(tmp, func, private_data);
527 free(tmp);
528 if (ret < 0)
529 goto out;
530 }
531 ret = 1;
532 out:
533 closedir(dir);
534 ret2 = para_fchdir(cwd_fd);
535 if (ret2 < 0 && ret >= 0)
536 ret = ret2;
537 close(cwd_fd);
538 return ret;
539 }