Rename write_nonblock() to xwrite().
[paraslash.git] / fd.c
1 /*
2 * Copyright (C) 2006-2012 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-writing on short writes.
23 *
24 * \param fd The file descriptor.
25 * \param buf The buffer to write.
26 * \param len The number of bytes to write.
27 *
28 * EAGAIN/EWOULDBLOCK is not considered a fatal error condition. For example
29 * DCCP CCID3 has a sending wait queue which fills up and is emptied
30 * asynchronously. The EAGAIN case means that there is currently no space in
31 * the wait queue, but this can change at any moment.
32 *
33 * \return Negative on fatal errors, number of bytes written else. For blocking
34 * file descriptors this function returns either \a len or the error code of
35 * the fatal error that caused the last write call to fail. For nonblocking
36 * file descriptors there is a third possibility: A positive return value < \a
37 * len indicates that some bytes have been written but the next write would
38 * block.
39 */
40 int xwrite(int fd, const char *buf, size_t len)
41 {
42 size_t written = 0;
43
44 while (written < len) {
45 ssize_t ret = write(fd, buf + written, len - written);
46 if (ret >= 0) {
47 written += ret;
48 continue;
49 }
50 if (errno == EINTR)
51 /*
52 * The write() call was interrupted by a signal before
53 * any data was written. Try again.
54 */
55 continue;
56 if (errno == EAGAIN || errno == EWOULDBLOCK)
57 /*
58 * We don't consider this an error. Note that POSIX
59 * allows either error to be returned, and does not
60 * require these constants to have the same value.
61 */
62 return written;
63 /* fatal error */
64 return -ERRNO_TO_PARA_ERROR(errno);
65 }
66 return written;
67 }
68
69 /**
70 * Write all data to a file descriptor.
71 *
72 * \param fd The file descriptor.
73 * \param buf The buffer to be sent.
74 * \param len The length of \a buf.
75 *
76 * This is like \ref xwrite() but returns \p -E_SHORT_WRITE if not
77 * all data could be written.
78 *
79 * \return Number of bytes written on success, negative error code else.
80 */
81 int write_all(int fd, const char *buf, size_t len)
82 {
83 int ret = xwrite(fd, buf, len);
84
85 if (ret < 0)
86 return ret;
87 if (ret != len)
88 return -E_SHORT_WRITE;
89 return ret;
90 }
91
92 /**
93 * Write a buffer given by a format string.
94 *
95 * \param fd The file descriptor.
96 * \param fmt A format string.
97 *
98 * \return The return value of the underlying call to \ref write_all().
99 */
100 __printf_2_3 int write_va_buffer(int fd, const char *fmt, ...)
101 {
102 char *msg;
103 int ret;
104
105 PARA_VSPRINTF(fmt, msg);
106 ret = write_buffer(fd, msg);
107 free(msg);
108 return ret;
109 }
110
111 /**
112 * Read from a non-blocking file descriptor into multiple buffers.
113 *
114 * \param fd The file descriptor to read from.
115 * \param iov Scatter/gather array used in readv().
116 * \param iovcnt Number of elements in \a iov.
117 * \param rfds An optional fd set pointer.
118 * \param num_bytes Result pointer. Contains the number of bytes read from \a fd.
119 *
120 * If \a rfds is not \p NULL and the (non-blocking) file descriptor \a fd is
121 * not set in \a rfds, this function returns early without doing anything.
122 * Otherwise The function tries to read up to \a sz bytes from \a fd. As for
123 * xwrite(), EAGAIN is not considered an error condition. However, EOF
124 * is.
125 *
126 * \return Zero or a negative error code. If the underlying call to readv(2)
127 * returned zero (indicating an end of file condition) or failed for some
128 * reason other than \p EAGAIN, a negative return value is returned.
129 *
130 * In any case, \a num_bytes contains the number of bytes that have been
131 * successfully read from \a fd (zero if the first readv() call failed with
132 * EAGAIN). Note that even if the function returns negative, some data might
133 * have been read before the error occurred. In this case \a num_bytes is
134 * positive.
135 *
136 * \sa \ref xwrite(), read(2), readv(2).
137 */
138 int readv_nonblock(int fd, struct iovec *iov, int iovcnt, fd_set *rfds,
139 size_t *num_bytes)
140 {
141 int ret, i, j;
142
143 *num_bytes = 0;
144 /*
145 * Avoid a shortcoming of select(): Reads from a non-blocking fd might
146 * return EAGAIN even if FD_ISSET() returns true. However, FD_ISSET()
147 * returning false definitely means that no data can currently be read.
148 * This is the common case, so it is worth to avoid the overhead of the
149 * read() system call in this case.
150 */
151 if (rfds && !FD_ISSET(fd, rfds))
152 return 0;
153
154 for (i = 0, j = 0; i < iovcnt;) {
155
156 /* fix up the first iov */
157 assert(j < iov[i].iov_len);
158 iov[i].iov_base += j;
159 iov[i].iov_len -= j;
160 ret = readv(fd, iov + i, iovcnt - i);
161 iov[i].iov_base -= j;
162 iov[i].iov_len += j;
163
164 if (ret == 0)
165 return -E_EOF;
166 if (ret < 0) {
167 if (errno == EAGAIN)
168 return 0;
169 return -ERRNO_TO_PARA_ERROR(errno);
170 }
171 *num_bytes += ret;
172 while (ret > 0) {
173 if (ret < iov[i].iov_len - j) {
174 j += ret;
175 break;
176 }
177 ret -= iov[i].iov_len - j;
178 j = 0;
179 if (++i >= iovcnt)
180 break;
181 }
182 }
183 return 0;
184 }
185
186 /**
187 * Read from a non-blocking file descriptor into a single buffer.
188 *
189 * \param fd The file descriptor to read from.
190 * \param buf The buffer to read data to.
191 * \param sz The size of \a buf.
192 * \param rfds \see \ref readv_nonblock().
193 * \param num_bytes \see \ref readv_nonblock().
194 *
195 * This is a simple wrapper for readv_nonblock() which uses an iovec with a single
196 * buffer.
197 *
198 * \return The return value of the underlying call to readv_nonblock().
199 */
200 int read_nonblock(int fd, void *buf, size_t sz, fd_set *rfds, size_t *num_bytes)
201 {
202 struct iovec iov = {.iov_base = buf, .iov_len = sz};
203 return readv_nonblock(fd, &iov, 1, rfds, num_bytes);
204 }
205
206 /**
207 * Read a buffer and check its content for a pattern.
208 *
209 * \param fd The file descriptor to receive from.
210 * \param pattern The expected pattern.
211 * \param bufsize The size of the internal buffer.
212 * \param rfds Passed to read_nonblock().
213 *
214 * This function tries to read at most \a bufsize bytes from the non-blocking
215 * file descriptor \a fd. If at least \p strlen(\a pattern) bytes have been
216 * received, the beginning of the received buffer is compared with \a pattern,
217 * ignoring case.
218 *
219 * \return Positive if \a pattern was received, negative on errors, zero if no data
220 * was available to read.
221 *
222 * \sa \ref read_nonblock(), \sa strncasecmp(3).
223 */
224 int read_pattern(int fd, const char *pattern, size_t bufsize, fd_set *rfds)
225 {
226 size_t n, len;
227 char *buf = para_malloc(bufsize + 1);
228 int ret = read_nonblock(fd, buf, bufsize, rfds, &n);
229
230 buf[n] = '\0';
231 if (ret < 0)
232 goto out;
233 ret = 0;
234 if (n == 0)
235 goto out;
236 ret = -E_READ_PATTERN;
237 len = strlen(pattern);
238 if (n < len)
239 goto out;
240 if (strncasecmp(buf, pattern, len) != 0)
241 goto out;
242 ret = 1;
243 out:
244 if (ret < 0) {
245 PARA_NOTICE_LOG("%s\n", para_strerror(-ret));
246 PARA_NOTICE_LOG("recvd %zu bytes: %s\n", n, buf);
247 }
248 free(buf);
249 return ret;
250 }
251
252 /**
253 * Check whether a file exists.
254 *
255 * \param fn The file name.
256 *
257 * \return Non-zero iff file exists.
258 */
259 int file_exists(const char *fn)
260 {
261 struct stat statbuf;
262
263 return !stat(fn, &statbuf);
264 }
265
266 /**
267 * Paraslash's wrapper for select(2).
268 *
269 * It calls select(2) (with no exceptfds) and starts over if select() was
270 * interrupted by a signal.
271 *
272 * \param n The highest-numbered descriptor in any of the two sets, plus 1.
273 * \param readfds fds that should be checked for readability.
274 * \param writefds fds that should be checked for writablility.
275 * \param timeout_tv upper bound on the amount of time elapsed before select()
276 * returns.
277 *
278 * \return The return value of the underlying select() call on success, the
279 * negative system error code on errors.
280 *
281 * All arguments are passed verbatim to select(2).
282 * \sa select(2) select_tut(2).
283 */
284 int para_select(int n, fd_set *readfds, fd_set *writefds,
285 struct timeval *timeout_tv)
286 {
287 int ret;
288 do
289 ret = select(n, readfds, writefds, NULL, timeout_tv);
290 while (ret < 0 && errno == EINTR);
291 if (ret < 0)
292 return -ERRNO_TO_PARA_ERROR(errno);
293 return ret;
294 }
295
296 /**
297 * Set a file descriptor to blocking mode.
298 *
299 * \param fd The file descriptor.
300 *
301 * \return Standard.
302 */
303 __must_check int mark_fd_blocking(int fd)
304 {
305 int flags = fcntl(fd, F_GETFL);
306 if (flags < 0)
307 return -ERRNO_TO_PARA_ERROR(errno);
308 flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
309 if (flags < 0)
310 return -ERRNO_TO_PARA_ERROR(errno);
311 return 1;
312 }
313
314 /**
315 * Set a file descriptor to non-blocking mode.
316 *
317 * \param fd The file descriptor.
318 *
319 * \return Standard.
320 */
321 __must_check int mark_fd_nonblocking(int fd)
322 {
323 int flags = fcntl(fd, F_GETFL);
324 if (flags < 0)
325 return -ERRNO_TO_PARA_ERROR(errno);
326 flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
327 if (flags < 0)
328 return -ERRNO_TO_PARA_ERROR(errno);
329 return 1;
330 }
331
332 /**
333 * Set a file descriptor in a fd_set.
334 *
335 * \param fd The file descriptor to be set.
336 * \param fds The file descriptor set.
337 * \param max_fileno Highest-numbered file descriptor.
338 *
339 * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
340 * return, \a max_fileno contains the maximum of the old_value and \a fd.
341 *
342 * \sa para_select.
343 */
344 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
345 {
346 assert(fd >= 0 && fd < FD_SETSIZE);
347 #if 0
348 {
349 int flags = fcntl(fd, F_GETFL);
350 if (!(flags & O_NONBLOCK)) {
351 PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
352 exit(EXIT_FAILURE);
353 }
354 }
355 #endif
356 FD_SET(fd, fds);
357 *max_fileno = PARA_MAX(*max_fileno, fd);
358 }
359
360 /**
361 * Paraslash's wrapper for fgets(3).
362 *
363 * \param line Pointer to the buffer to store the line.
364 * \param size The size of the buffer given by \a line.
365 * \param f The stream to read from.
366 *
367 * \return Unlike the standard fgets() function, an integer value
368 * is returned. On success, this function returns 1. On errors, -E_FGETS
369 * is returned. A zero return value indicates an end of file condition.
370 */
371 __must_check int para_fgets(char *line, int size, FILE *f)
372 {
373 again:
374 if (fgets(line, size, f))
375 return 1;
376 if (feof(f))
377 return 0;
378 if (!ferror(f))
379 return -E_FGETS;
380 if (errno != EINTR) {
381 PARA_ERROR_LOG("%s\n", strerror(errno));
382 return -E_FGETS;
383 }
384 clearerr(f);
385 goto again;
386 }
387
388 /**
389 * Paraslash's wrapper for mmap.
390 *
391 * \param length Number of bytes to mmap.
392 * \param prot Either PROT_NONE or the bitwise OR of one or more of
393 * PROT_EXEC PROT_READ PROT_WRITE.
394 * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
395 * \param fd The file to mmap from.
396 * \param offset Mmap start.
397 * \param map Result pointer.
398 *
399 * \return Standard.
400 *
401 * \sa mmap(2).
402 */
403 int para_mmap(size_t length, int prot, int flags, int fd, off_t offset,
404 void *map)
405 {
406 void **m = map;
407
408 errno = EINVAL;
409 if (!length)
410 goto err;
411 *m = mmap(NULL, length, prot, flags, fd, offset);
412 if (*m != MAP_FAILED)
413 return 1;
414 err:
415 *m = NULL;
416 return -ERRNO_TO_PARA_ERROR(errno);
417 }
418
419 /**
420 * Wrapper for the open(2) system call.
421 *
422 * \param path The filename.
423 * \param flags The usual open(2) flags.
424 * \param mode Specifies the permissions to use.
425 *
426 * The mode parameter must be specified when O_CREAT is in the flags, and is
427 * ignored otherwise.
428 *
429 * \return The file descriptor on success, negative on errors.
430 *
431 * \sa open(2).
432 */
433 int para_open(const char *path, int flags, mode_t mode)
434 {
435 int ret = open(path, flags, mode);
436
437 if (ret >= 0)
438 return ret;
439 return -ERRNO_TO_PARA_ERROR(errno);
440 }
441
442 /**
443 * Wrapper for chdir(2).
444 *
445 * \param path The specified directory.
446 *
447 * \return Standard.
448 */
449 int para_chdir(const char *path)
450 {
451 int ret = chdir(path);
452
453 if (ret >= 0)
454 return 1;
455 return -ERRNO_TO_PARA_ERROR(errno);
456 }
457
458 /**
459 * Save the cwd and open a given directory.
460 *
461 * \param dirname Path to the directory to open.
462 * \param dir Result pointer.
463 * \param cwd File descriptor of the current working directory.
464 *
465 * \return Standard.
466 *
467 * Opening the current directory (".") and calling fchdir() to return is
468 * usually faster and more reliable than saving cwd in some buffer and calling
469 * chdir() afterwards.
470 *
471 * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
472 * stored in \a cwd. If the function returns success, and \a cwd is not \p
473 * NULL, the caller must close this file descriptor (probably after calling
474 * fchdir(*cwd)).
475 *
476 * On errors, the function undos everything, so the caller needs neither close
477 * any files, nor change back to the original working directory.
478 *
479 * \sa getcwd(3).
480 *
481 */
482 static int para_opendir(const char *dirname, DIR **dir, int *cwd)
483 {
484 int ret;
485
486 if (cwd) {
487 ret = para_open(".", O_RDONLY, 0);
488 if (ret < 0)
489 return ret;
490 *cwd = ret;
491 }
492 ret = para_chdir(dirname);
493 if (ret < 0)
494 goto close_cwd;
495 *dir = opendir(".");
496 if (*dir)
497 return 1;
498 ret = -ERRNO_TO_PARA_ERROR(errno);
499 /* Ignore return value of fchdir() and close(). We're busted anyway. */
500 if (cwd) {
501 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
502 }
503 close_cwd:
504 if (cwd)
505 close(*cwd);
506 return ret;
507 }
508
509 /**
510 * A wrapper for fchdir().
511 *
512 * \param fd An open file descriptor.
513 *
514 * \return Standard.
515 */
516 static int para_fchdir(int fd)
517 {
518 if (fchdir(fd) < 0)
519 return -ERRNO_TO_PARA_ERROR(errno);
520 return 1;
521 }
522
523 /**
524 * A wrapper for mkdir(2).
525 *
526 * \param path Name of the directory to create.
527 * \param mode The permissions to use.
528 *
529 * \return Standard.
530 */
531 int para_mkdir(const char *path, mode_t mode)
532 {
533 if (!mkdir(path, mode))
534 return 1;
535 return -ERRNO_TO_PARA_ERROR(errno);
536 }
537
538 /**
539 * Open a file and map it into memory.
540 *
541 * \param path Name of the regular file to map.
542 * \param open_mode Either \p O_RDONLY or \p O_RDWR.
543 * \param map On success, the mapping is returned here.
544 * \param size size of the mapping.
545 * \param fd_ptr The file descriptor of the mapping.
546 *
547 * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
548 * open call is closed after mmap(). Otherwise the file is kept open and the
549 * file descriptor is returned in \a fd_ptr.
550 *
551 * \return Standard.
552 *
553 * \sa para_open(), mmap(2).
554 */
555 int mmap_full_file(const char *path, int open_mode, void **map,
556 size_t *size, int *fd_ptr)
557 {
558 int fd, ret, mmap_prot, mmap_flags;
559 struct stat file_status;
560
561 if (open_mode == O_RDONLY) {
562 mmap_prot = PROT_READ;
563 mmap_flags = MAP_PRIVATE;
564 } else {
565 mmap_prot = PROT_READ | PROT_WRITE;
566 mmap_flags = MAP_SHARED;
567 }
568 ret = para_open(path, open_mode, 0);
569 if (ret < 0)
570 return ret;
571 fd = ret;
572 if (fstat(fd, &file_status) < 0) {
573 ret = -ERRNO_TO_PARA_ERROR(errno);
574 goto out;
575 }
576 *size = file_status.st_size;
577 ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
578 out:
579 if (ret < 0 || !fd_ptr)
580 close(fd);
581 else
582 *fd_ptr = fd;
583 return ret;
584 }
585
586 /**
587 * A wrapper for munmap(2).
588 *
589 * \param start The start address of the memory mapping.
590 * \param length The size of the mapping.
591 *
592 * \return Standard.
593 *
594 * \sa munmap(2), mmap_full_file().
595 */
596 int para_munmap(void *start, size_t length)
597 {
598 int err;
599
600 if (!start)
601 return 0;
602 if (munmap(start, length) >= 0)
603 return 1;
604 err = errno;
605 PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
606 strerror(err));
607 return -ERRNO_TO_PARA_ERROR(err);
608 }
609
610 /**
611 * Check a file descriptor for writability.
612 *
613 * \param fd The file descriptor.
614 *
615 * \return positive if fd is ready for writing, zero if it isn't, negative if
616 * an error occurred.
617 */
618
619 int write_ok(int fd)
620 {
621 struct timeval tv;
622 fd_set wfds;
623
624 FD_ZERO(&wfds);
625 FD_SET(fd, &wfds);
626 tv.tv_sec = 0;
627 tv.tv_usec = 0;
628 return para_select(fd + 1, NULL, &wfds, &tv);
629 }
630
631 /**
632 * Ensure that file descriptors 0, 1, and 2 are valid.
633 *
634 * Common approach that opens /dev/null until it gets a file descriptor greater
635 * than two.
636 *
637 * \sa okir's Black Hats Manual.
638 */
639 void valid_fd_012(void)
640 {
641 while (1) {
642 int fd = open("/dev/null", O_RDWR);
643 if (fd < 0)
644 exit(EXIT_FAILURE);
645 if (fd > 2) {
646 close(fd);
647 break;
648 }
649 }
650 }
651
652 /**
653 * Traverse the given directory recursively.
654 *
655 * \param dirname The directory to traverse.
656 * \param func The function to call for each entry.
657 * \param private_data Pointer to an arbitrary data structure.
658 *
659 * For each regular file under \a dirname, the supplied function \a func is
660 * called. The full path of the regular file and the \a private_data pointer
661 * are passed to \a func. Directories for which the calling process has no
662 * permissions to change to are silently ignored.
663 *
664 * \return Standard.
665 */
666 int for_each_file_in_dir(const char *dirname,
667 int (*func)(const char *, void *), void *private_data)
668 {
669 DIR *dir;
670 struct dirent *entry;
671 int cwd_fd, ret2, ret = para_opendir(dirname, &dir, &cwd_fd);
672
673 if (ret < 0)
674 return ret == -ERRNO_TO_PARA_ERROR(EACCES)? 1 : ret;
675 /* scan cwd recursively */
676 while ((entry = readdir(dir))) {
677 mode_t m;
678 char *tmp;
679 struct stat s;
680
681 if (!strcmp(entry->d_name, "."))
682 continue;
683 if (!strcmp(entry->d_name, ".."))
684 continue;
685 if (lstat(entry->d_name, &s) == -1)
686 continue;
687 m = s.st_mode;
688 if (!S_ISREG(m) && !S_ISDIR(m))
689 continue;
690 tmp = make_message("%s/%s", dirname, entry->d_name);
691 if (!S_ISDIR(m)) {
692 ret = func(tmp, private_data);
693 free(tmp);
694 if (ret < 0)
695 goto out;
696 continue;
697 }
698 /* directory */
699 ret = for_each_file_in_dir(tmp, func, private_data);
700 free(tmp);
701 if (ret < 0)
702 goto out;
703 }
704 ret = 1;
705 out:
706 closedir(dir);
707 ret2 = para_fchdir(cwd_fd);
708 if (ret2 < 0 && ret >= 0)
709 ret = ret2;
710 close(cwd_fd);
711 return ret;
712 }