Introduce the new nonblock API.
[paraslash.git] / fd.c
1 /*
2 * Copyright (C) 2006-2010 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 <regex.h>
10 #include <sys/types.h>
11 #include <dirent.h>
12 #include <sys/mman.h>
13 #include <fcntl.h>
14 #include <sys/uio.h>
15
16 #include "para.h"
17 #include "error.h"
18 #include "string.h"
19 #include "fd.h"
20
21 /**
22 * Write a buffer to a file descriptor, re-write on short writes.
23 *
24 * \param fd The file descriptor.
25 * \param buf The buffer to be sent.
26 * \param len The length of \a buf.
27 *
28 * \return Standard. In any case, the number of bytes that have been written is
29 * stored in \a len.
30 */
31 int write_all(int fd, const char *buf, size_t *len)
32 {
33 size_t total = *len;
34
35 assert(total);
36 *len = 0;
37 while (*len < total) {
38 int ret = write(fd, buf + *len, total - *len);
39 if (ret == -1)
40 return -ERRNO_TO_PARA_ERROR(errno);
41 *len += ret;
42 }
43 return 1;
44 }
45
46 /**
47 * Write a buffer to a non-blocking file descriptor.
48 *
49 * \param fd The file descriptor.
50 * \param buf the buffer to write.
51 * \param len the number of bytes of \a buf.
52 * \param max_bytes_per_write Do not write more than that many bytes at once.
53 *
54 * If \a max_bytes_per_write is non-zero, do not send more than that many bytes
55 * per write().
56 *
57 * EAGAIN is not considered an error condition. For example CCID3 has a
58 * sending wait queue which fills up and is emptied asynchronously. The EAGAIN
59 * case means that there is currently no space in the wait queue, but this can
60 * change at any moment.
61 *
62 * \return Negative on errors, number of bytes written else.
63 */
64 int write_nonblock(int fd, const char *buf, size_t len,
65 size_t max_bytes_per_write)
66 {
67 size_t written = 0;
68 int ret = 0;
69
70 while (written < len) {
71 size_t num = len - written;
72
73 if (max_bytes_per_write && max_bytes_per_write < num)
74 num = max_bytes_per_write;
75 ret = write(fd, buf + written, num);
76 if (ret < 0 && errno == EAGAIN)
77 return written;
78 if (ret < 0)
79 return -ERRNO_TO_PARA_ERROR(errno);
80 written += ret;
81 }
82 return written;
83 }
84
85 /**
86 * Read from a non-blocking file descriptor into multiple buffers.
87 *
88 * \param fd The file descriptor to read from.
89 * \param iov Scatter/gather array used in readv().
90 * \param iovcnt Number of elements in \a iov.
91 * \param rfds An optional fd set pointer.
92 * \param num_bytes Result pointer. Contains the number of bytes read from \a fd.
93 *
94 * If \a rfds is not \p NULL and the (non-blocking) file descriptor \a fd is
95 * not set in \a rfds, this function returns early without doing anything.
96 * Otherwise The function tries to read up to \a sz bytes from \a fd. As for
97 * write_nonblock(), EAGAIN is not considered an error condition. However, EOF
98 * is.
99 *
100 * \return Zero or a negative error code. If the underlying call to readv(2)
101 * returned zero (indicating an end of file condition) or failed for some
102 * reason other than \p EAGAIN, a negative return value is returned.
103 *
104 * In any case, \a num_bytes contains the number of bytes that have been
105 * successfully read from \a fd (zero if the first readv() call failed with
106 * EAGAIN). Note that even if the function returns negative, some data might
107 * have been read before the error occured. In this case \a num_bytes is
108 * positive.
109 *
110 * \sa \ref write_nonblock(), read(2), readv(2).
111 */
112 int readv_nonblock(int fd, struct iovec *iov, int iovcnt, fd_set *rfds,
113 size_t *num_bytes)
114 {
115 int ret, i, j;
116
117 *num_bytes = 0;
118 /*
119 * Avoid a shortcoming of select(): Reads from a non-blocking fd might
120 * return EAGAIN even if FD_ISSET() returns true. However, FD_ISSET()
121 * returning false definitely means that no data can currently be read.
122 * This is the common case, so it is worth to avoid the overhead of the
123 * read() system call in this case.
124 */
125 if (rfds && !FD_ISSET(fd, rfds))
126 return 0;
127
128 for (i = 0, j = 0; i < iovcnt;) {
129
130 /* fix up the first iov */
131 assert(j < iov[i].iov_len);
132 iov[i].iov_base += j;
133 iov[i].iov_len -= j;
134 ret = readv(fd, iov + i, iovcnt - i);
135 iov[i].iov_base -= j;
136 iov[i].iov_len += j;
137
138 if (ret == 0)
139 return -E_EOF;
140 if (ret < 0) {
141 if (errno == EAGAIN)
142 return 0;
143 return -ERRNO_TO_PARA_ERROR(errno);
144 }
145 *num_bytes += ret;
146 while (ret > 0) {
147 if (ret < iov[i].iov_len - j) {
148 j += ret;
149 break;
150 }
151 ret -= iov[i].iov_len - j;
152 j = 0;
153 if (++i >= iovcnt)
154 break;
155 }
156 }
157 return 0;
158 }
159
160 /**
161 * Read from a non-blocking file descriptor into a single buffer.
162 *
163 * \param fd The file descriptor to read from.
164 * \param buf The buffer to read data to.
165 * \param sz The size of \a buf.
166 * \param rfds \see \ref readv_nonblock().
167 * \param num_bytes \see \ref readv_nonblock().
168 *
169 * This is a simple wrapper for readv_nonblock() which uses an iovec with a single
170 * buffer.
171 *
172 * \return The return value of the underlying call to readv_nonblock().
173 */
174 int read_nonblock(int fd, void *buf, size_t sz, fd_set *rfds, size_t *num_bytes)
175 {
176 struct iovec iov = {.iov_base = buf, .iov_len = sz};
177 return readv_nonblock(fd, &iov, 1, rfds, num_bytes);
178 }
179
180 /**
181 * Simple wrapper for readv().
182 *
183 * \param fd The file descriptor to read from.
184 * \param iov Scatter/gather array used in readv().
185 * \param iovcnt Number of elements in \a iov.
186 *
187 * \return A negative error code on errors, the return value of the underlying
188 * call to readv() otherwise.
189 *
190 * \sa readv(2).
191 */
192 int para_readv(int fd, struct iovec *iov, int iovcnt)
193 {
194 int ret = readv(fd, iov, iovcnt);
195
196 if (ret < 0)
197 return -ERRNO_TO_PARA_ERROR(errno);
198 return ret;
199 }
200
201 /**
202 * Check whether a file exists.
203 *
204 * \param fn The file name.
205 *
206 * \return Non-zero iff file exists.
207 */
208 int file_exists(const char *fn)
209 {
210 struct stat statbuf;
211
212 return !stat(fn, &statbuf);
213 }
214
215 /**
216 * Paraslash's wrapper for select(2).
217 *
218 * It calls select(2) (with no exceptfds) and starts over if select() was
219 * interrupted by a signal.
220 *
221 * \param n The highest-numbered descriptor in any of the two sets, plus 1.
222 * \param readfds fds that should be checked for readability.
223 * \param writefds fds that should be checked for writablility.
224 * \param timeout_tv upper bound on the amount of time elapsed before select()
225 * returns.
226 *
227 * \return The return value of the underlying select() call on success, the
228 * negative system error code on errors.
229 *
230 * All arguments are passed verbatim to select(2).
231 * \sa select(2) select_tut(2).
232 */
233 int para_select(int n, fd_set *readfds, fd_set *writefds,
234 struct timeval *timeout_tv)
235 {
236 int ret;
237 do
238 ret = select(n, readfds, writefds, NULL, timeout_tv);
239 while (ret < 0 && errno == EINTR);
240 if (ret < 0)
241 return -ERRNO_TO_PARA_ERROR(errno);
242 return ret;
243 }
244
245 /**
246 * Set a file descriptor to blocking mode.
247 *
248 * \param fd The file descriptor.
249 *
250 * \return Standard.
251 */
252 __must_check int mark_fd_blocking(int fd)
253 {
254 int flags = fcntl(fd, F_GETFL);
255 if (flags < 0)
256 return -ERRNO_TO_PARA_ERROR(errno);
257 flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
258 if (flags < 0)
259 return -ERRNO_TO_PARA_ERROR(errno);
260 return 1;
261 }
262
263 /**
264 * Set a file descriptor to non-blocking mode.
265 *
266 * \param fd The file descriptor.
267 *
268 * \return Standard.
269 */
270 __must_check int mark_fd_nonblocking(int fd)
271 {
272 int flags = fcntl(fd, F_GETFL);
273 if (flags < 0)
274 return -ERRNO_TO_PARA_ERROR(errno);
275 flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
276 if (flags < 0)
277 return -ERRNO_TO_PARA_ERROR(errno);
278 return 1;
279 }
280
281 /**
282 * Set a file descriptor in a fd_set.
283 *
284 * \param fd The file descriptor to be set.
285 * \param fds The file descriptor set.
286 * \param max_fileno Highest-numbered file descriptor.
287 *
288 * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
289 * return, \a max_fileno contains the maximum of the old_value and \a fd.
290 *
291 * \sa para_select.
292 */
293 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
294 {
295 assert(fd >= 0 && fd < FD_SETSIZE);
296 #if 0
297 {
298 int flags = fcntl(fd, F_GETFL);
299 if (!(flags & O_NONBLOCK)) {
300 PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
301 exit(EXIT_FAILURE);
302 }
303 }
304 #endif
305 FD_SET(fd, fds);
306 *max_fileno = PARA_MAX(*max_fileno, fd);
307 }
308
309 /**
310 * Paraslash's wrapper for fgets(3).
311 *
312 * \param line Pointer to the buffer to store the line.
313 * \param size The size of the buffer given by \a line.
314 * \param f The stream to read from.
315 *
316 * \return Unlike the standard fgets() function, an integer value
317 * is returned. On success, this function returns 1. On errors, -E_FGETS
318 * is returned. A zero return value indicates an end of file condition.
319 */
320 __must_check int para_fgets(char *line, int size, FILE *f)
321 {
322 again:
323 if (fgets(line, size, f))
324 return 1;
325 if (feof(f))
326 return 0;
327 if (!ferror(f))
328 return -E_FGETS;
329 if (errno != EINTR) {
330 PARA_ERROR_LOG("%s\n", strerror(errno));
331 return -E_FGETS;
332 }
333 clearerr(f);
334 goto again;
335 }
336
337 /**
338 * Paraslash's wrapper for mmap.
339 *
340 * \param length Number of bytes to mmap.
341 * \param prot Either PROT_NONE or the bitwise OR of one or more of
342 * PROT_EXEC PROT_READ PROT_WRITE.
343 * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
344 * \param fd The file to mmap from.
345 * \param offset Mmap start.
346 * \param map Result pointer.
347 *
348 * \return Standard.
349 *
350 * \sa mmap(2).
351 */
352 int para_mmap(size_t length, int prot, int flags, int fd, off_t offset,
353 void *map)
354 {
355 void **m = map;
356
357 errno = EINVAL;
358 if (!length)
359 goto err;
360 *m = mmap(NULL, length, prot, flags, fd, offset);
361 if (*m != MAP_FAILED)
362 return 1;
363 err:
364 *m = NULL;
365 return -ERRNO_TO_PARA_ERROR(errno);
366 }
367
368 /**
369 * Wrapper for the open(2) system call.
370 *
371 * \param path The filename.
372 * \param flags The usual open(2) flags.
373 * \param mode Specifies the permissions to use.
374 *
375 * The mode parameter must be specified when O_CREAT is in the flags, and is
376 * ignored otherwise.
377 *
378 * \return The file descriptor on success, negative on errors.
379 *
380 * \sa open(2).
381 */
382 int para_open(const char *path, int flags, mode_t mode)
383 {
384 int ret = open(path, flags, mode);
385
386 if (ret >= 0)
387 return ret;
388 return -ERRNO_TO_PARA_ERROR(errno);
389 }
390
391 /**
392 * Wrapper for chdir(2).
393 *
394 * \param path The specified directory.
395 *
396 * \return Standard.
397 */
398 int para_chdir(const char *path)
399 {
400 int ret = chdir(path);
401
402 if (ret >= 0)
403 return 1;
404 return -ERRNO_TO_PARA_ERROR(errno);
405 }
406
407 /**
408 * Save the cwd and open a given directory.
409 *
410 * \param dirname Path to the directory to open.
411 * \param dir Result pointer.
412 * \param cwd File descriptor of the current working directory.
413 *
414 * \return Standard.
415 *
416 * Opening the current directory (".") and calling fchdir() to return is
417 * usually faster and more reliable than saving cwd in some buffer and calling
418 * chdir() afterwards.
419 *
420 * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
421 * stored in \a cwd. If the function returns success, and \a cwd is not \p
422 * NULL, the caller must close this file descriptor (probably after calling
423 * fchdir(*cwd)).
424 *
425 * On errors, the function undos everything, so the caller needs neither close
426 * any files, nor change back to the original working directory.
427 *
428 * \sa getcwd(3).
429 *
430 */
431 int para_opendir(const char *dirname, DIR **dir, int *cwd)
432 {
433 int ret;
434
435 if (cwd) {
436 ret = para_open(".", O_RDONLY, 0);
437 if (ret < 0)
438 return ret;
439 *cwd = ret;
440 }
441 ret = para_chdir(dirname);
442 if (ret < 0)
443 goto close_cwd;
444 *dir = opendir(".");
445 if (*dir)
446 return 1;
447 ret = -ERRNO_TO_PARA_ERROR(errno);
448 /* Ignore return value of fchdir() and close(). We're busted anyway. */
449 if (cwd) {
450 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
451 }
452 close_cwd:
453 if (cwd)
454 close(*cwd);
455 return ret;
456 }
457
458 /**
459 * A wrapper for fchdir().
460 *
461 * \param fd An open file descriptor.
462 *
463 * \return Standard.
464 */
465 int para_fchdir(int fd)
466 {
467 if (fchdir(fd) < 0)
468 return -ERRNO_TO_PARA_ERROR(errno);
469 return 1;
470 }
471
472 /**
473 * A wrapper for mkdir(2).
474 *
475 * \param path Name of the directory to create.
476 * \param mode The permissions to use.
477 *
478 * \return Standard.
479 */
480 int para_mkdir(const char *path, mode_t mode)
481 {
482 if (!mkdir(path, mode))
483 return 1;
484 return -ERRNO_TO_PARA_ERROR(errno);
485 }
486
487 /**
488 * Open a file and map it into memory.
489 *
490 * \param path Name of the regular file to map.
491 * \param open_mode Either \p O_RDONLY or \p O_RDWR.
492 * \param map On success, the mapping is returned here.
493 * \param size size of the mapping.
494 * \param fd_ptr The file descriptor of the mapping.
495 *
496 * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
497 * open call is closed after mmap(). Otherwise the file is kept open and the
498 * file descriptor is returned in \a fd_ptr.
499 *
500 * \return Standard.
501 *
502 * \sa para_open(), mmap(2).
503 */
504 int mmap_full_file(const char *path, int open_mode, void **map,
505 size_t *size, int *fd_ptr)
506 {
507 int fd, ret, mmap_prot, mmap_flags;
508 struct stat file_status;
509
510 if (open_mode == O_RDONLY) {
511 mmap_prot = PROT_READ;
512 mmap_flags = MAP_PRIVATE;
513 } else {
514 mmap_prot = PROT_READ | PROT_WRITE;
515 mmap_flags = MAP_SHARED;
516 }
517 ret = para_open(path, open_mode, 0);
518 if (ret < 0)
519 return ret;
520 fd = ret;
521 if (fstat(fd, &file_status) < 0) {
522 ret = -ERRNO_TO_PARA_ERROR(errno);
523 goto out;
524 }
525 *size = file_status.st_size;
526 ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
527 out:
528 if (ret < 0 || !fd_ptr)
529 close(fd);
530 else
531 *fd_ptr = fd;
532 return ret;
533 }
534
535 /**
536 * A wrapper for munmap(2).
537 *
538 * \param start The start address of the memory mapping.
539 * \param length The size of the mapping.
540 *
541 * \return Standard.
542 *
543 * \sa munmap(2), mmap_full_file().
544 */
545 int para_munmap(void *start, size_t length)
546 {
547 int err;
548 if (munmap(start, length) >= 0)
549 return 1;
550 err = errno;
551 PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
552 strerror(err));
553 return -ERRNO_TO_PARA_ERROR(err);
554 }
555
556 /**
557 * Check a file descriptor for writability.
558 *
559 * \param fd The file descriptor.
560 *
561 * \return positive if fd is ready for writing, zero if it isn't, negative if
562 * an error occurred.
563 */
564
565 int write_ok(int fd)
566 {
567 struct timeval tv;
568 fd_set wfds;
569
570 FD_ZERO(&wfds);
571 FD_SET(fd, &wfds);
572 tv.tv_sec = 0;
573 tv.tv_usec = 0;
574 return para_select(fd + 1, NULL, &wfds, &tv);
575 }
576
577 /**
578 * Ensure that file descriptors 0, 1, and 2 are valid.
579 *
580 * Common approach that opens /dev/null until it gets a file descriptor greater
581 * than two.
582 *
583 * \sa okir's Black Hats Manual.
584 */
585 void valid_fd_012(void)
586 {
587 while (1) {
588 int fd = open("/dev/null", O_RDWR);
589 if (fd < 0)
590 exit(EXIT_FAILURE);
591 if (fd > 2) {
592 close(fd);
593 break;
594 }
595 }
596 }
597
598 /**
599 * Traverse the given directory recursively.
600 *
601 * \param dirname The directory to traverse.
602 * \param func The function to call for each entry.
603 * \param private_data Pointer to an arbitrary data structure.
604 *
605 * For each regular file under \a dirname, the supplied function \a func is
606 * called. The full path of the regular file and the \a private_data pointer
607 * are passed to \a func. Directories for which the calling process has no
608 * permissions to change to are silently ignored.
609 *
610 * \return Standard.
611 */
612 int for_each_file_in_dir(const char *dirname,
613 int (*func)(const char *, void *), void *private_data)
614 {
615 DIR *dir;
616 struct dirent *entry;
617 int cwd_fd, ret2, ret = para_opendir(dirname, &dir, &cwd_fd);
618
619 if (ret < 0)
620 return ret == -ERRNO_TO_PARA_ERROR(EACCES)? 1 : ret;
621 /* scan cwd recursively */
622 while ((entry = readdir(dir))) {
623 mode_t m;
624 char *tmp;
625 struct stat s;
626
627 if (!strcmp(entry->d_name, "."))
628 continue;
629 if (!strcmp(entry->d_name, ".."))
630 continue;
631 if (lstat(entry->d_name, &s) == -1)
632 continue;
633 m = s.st_mode;
634 if (!S_ISREG(m) && !S_ISDIR(m))
635 continue;
636 tmp = make_message("%s/%s", dirname, entry->d_name);
637 if (!S_ISDIR(m)) {
638 ret = func(tmp, private_data);
639 free(tmp);
640 if (ret < 0)
641 goto out;
642 continue;
643 }
644 /* directory */
645 ret = for_each_file_in_dir(tmp, func, private_data);
646 free(tmp);
647 if (ret < 0)
648 goto out;
649 }
650 ret = 1;
651 out:
652 closedir(dir);
653 ret2 = para_fchdir(cwd_fd);
654 if (ret2 < 0 && ret >= 0)
655 ret = ret2;
656 close(cwd_fd);
657 return ret;
658 }