Merge branch 't/allow_zero_btr_add'
[paraslash.git] / fd.c
1 /*
2 * Copyright (C) 2006-2013 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 an array of buffers to a file descriptor.
23 *
24 * \param fd The file descriptor.
25 * \param iov Pointer to one or more buffers.
26 * \param iovcnt The number of buffers.
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.
34 *
35 * For blocking file descriptors, this function returns either the sum of all
36 * buffer sizes, or the error code of the fatal error that caused the last
37 * write call to fail.
38 *
39 * For nonblocking file descriptors there is a third possibility: Any positive
40 * return value less than the sum of the buffer sizes indicates that some bytes
41 * have been written but the next write would block.
42 *
43 * \sa writev(2), \ref xwrite().
44 */
45 int xwritev(int fd, struct iovec *iov, int iovcnt)
46 {
47 size_t written = 0;
48 int i;
49 struct iovec saved_iov, *curiov;
50
51 i = 0;
52 curiov = iov;
53 saved_iov = *curiov;
54 while (i < iovcnt && curiov->iov_len > 0) {
55 ssize_t ret = writev(fd, curiov, iovcnt - i);
56 if (ret >= 0) {
57 written += ret;
58 while (ret > 0) {
59 if (ret < curiov->iov_len) {
60 curiov->iov_base += ret;
61 curiov->iov_len -= ret;
62 break;
63 }
64 ret -= curiov->iov_len;
65 *curiov = saved_iov;
66 i++;
67 if (i >= iovcnt)
68 return written;
69 curiov++;
70 saved_iov = *curiov;
71 }
72 continue;
73 }
74 if (errno == EINTR)
75 /*
76 * The write() call was interrupted by a signal before
77 * any data was written. Try again.
78 */
79 continue;
80 if (errno == EAGAIN || errno == EWOULDBLOCK)
81 /*
82 * We don't consider this an error. Note that POSIX
83 * allows either error to be returned, and does not
84 * require these constants to have the same value.
85 */
86 return written;
87 /* fatal error */
88 return -ERRNO_TO_PARA_ERROR(errno);
89 }
90 return written;
91 }
92
93 /**
94 * Write a buffer to a file descriptor, re-writing on short writes.
95 *
96 * \param fd The file descriptor.
97 * \param buf The buffer to write.
98 * \param len The number of bytes to write.
99 *
100 * This is a simple wrapper for \ref xwritev().
101 *
102 * \return The return value of the underlying call to \ref xwritev().
103 */
104 int xwrite(int fd, const char *buf, size_t len)
105 {
106 struct iovec iov = {.iov_base = (void *)buf, .iov_len = len};
107 return xwritev(fd, &iov, 1);
108 }
109
110 /**
111 * Write all data to a file descriptor.
112 *
113 * \param fd The file descriptor.
114 * \param buf The buffer to be sent.
115 * \param len The length of \a buf.
116 *
117 * This is like \ref xwrite() but returns \p -E_SHORT_WRITE if not
118 * all data could be written.
119 *
120 * \return Number of bytes written on success, negative error code else.
121 */
122 int write_all(int fd, const char *buf, size_t len)
123 {
124 int ret = xwrite(fd, buf, len);
125
126 if (ret < 0)
127 return ret;
128 if (ret != len)
129 return -E_SHORT_WRITE;
130 return ret;
131 }
132
133 /**
134 * Write a buffer given by a format string.
135 *
136 * \param fd The file descriptor.
137 * \param fmt A format string.
138 *
139 * \return The return value of the underlying call to \ref write_all().
140 */
141 __printf_2_3 int write_va_buffer(int fd, const char *fmt, ...)
142 {
143 char *msg;
144 int ret;
145 va_list ap;
146
147 va_start(ap, fmt);
148 ret = xvasprintf(&msg, fmt, ap);
149 ret = write_all(fd, msg, ret);
150 free(msg);
151 return ret;
152 }
153
154 /**
155 * Read from a non-blocking file descriptor into multiple buffers.
156 *
157 * \param fd The file descriptor to read from.
158 * \param iov Scatter/gather array used in readv().
159 * \param iovcnt Number of elements in \a iov.
160 * \param rfds An optional fd set pointer.
161 * \param num_bytes Result pointer. Contains the number of bytes read from \a fd.
162 *
163 * If \a rfds is not \p NULL and the (non-blocking) file descriptor \a fd is
164 * not set in \a rfds, this function returns early without doing anything.
165 * Otherwise The function tries to read up to \a sz bytes from \a fd, where \a
166 * sz is the sum of the lengths of all vectors in \a iov. As for xwrite(),
167 * \p EAGAIN is not considered an error condition. However, \p EOF is.
168 *
169 * \return Zero or a negative error code. If the underlying call to readv(2)
170 * returned zero (indicating an end of file condition) or failed for some
171 * reason other than \p EAGAIN, a negative return value is returned.
172 *
173 * In any case, \a num_bytes contains the number of bytes that have been
174 * successfully read from \a fd (zero if the first readv() call failed with
175 * EAGAIN). Note that even if the function returns negative, some data might
176 * have been read before the error occurred. In this case \a num_bytes is
177 * positive.
178 *
179 * \sa \ref xwrite(), read(2), readv(2).
180 */
181 int readv_nonblock(int fd, struct iovec *iov, int iovcnt, fd_set *rfds,
182 size_t *num_bytes)
183 {
184 int ret, i, j;
185
186 *num_bytes = 0;
187 /*
188 * Avoid a shortcoming of select(): Reads from a non-blocking fd might
189 * return EAGAIN even if FD_ISSET() returns true. However, FD_ISSET()
190 * returning false definitely means that no data can currently be read.
191 * This is the common case, so it is worth to avoid the overhead of the
192 * read() system call in this case.
193 */
194 if (rfds && !FD_ISSET(fd, rfds))
195 return 0;
196
197 for (i = 0, j = 0; i < iovcnt;) {
198
199 /* fix up the first iov */
200 assert(j < iov[i].iov_len);
201 iov[i].iov_base += j;
202 iov[i].iov_len -= j;
203 ret = readv(fd, iov + i, iovcnt - i);
204 iov[i].iov_base -= j;
205 iov[i].iov_len += j;
206
207 if (ret == 0)
208 return -E_EOF;
209 if (ret < 0) {
210 if (errno == EAGAIN)
211 return 0;
212 return -ERRNO_TO_PARA_ERROR(errno);
213 }
214 *num_bytes += ret;
215 while (ret > 0) {
216 if (ret < iov[i].iov_len - j) {
217 j += ret;
218 break;
219 }
220 ret -= iov[i].iov_len - j;
221 j = 0;
222 if (++i >= iovcnt)
223 break;
224 }
225 }
226 return 0;
227 }
228
229 /**
230 * Read from a non-blocking file descriptor into a single buffer.
231 *
232 * \param fd The file descriptor to read from.
233 * \param buf The buffer to read data to.
234 * \param sz The size of \a buf.
235 * \param rfds \see \ref readv_nonblock().
236 * \param num_bytes \see \ref readv_nonblock().
237 *
238 * This is a simple wrapper for readv_nonblock() which uses an iovec with a single
239 * buffer.
240 *
241 * \return The return value of the underlying call to readv_nonblock().
242 */
243 int read_nonblock(int fd, void *buf, size_t sz, fd_set *rfds, size_t *num_bytes)
244 {
245 struct iovec iov = {.iov_base = buf, .iov_len = sz};
246 return readv_nonblock(fd, &iov, 1, rfds, num_bytes);
247 }
248
249 /**
250 * Read a buffer and check its content for a pattern.
251 *
252 * \param fd The file descriptor to receive from.
253 * \param pattern The expected pattern.
254 * \param bufsize The size of the internal buffer.
255 * \param rfds Passed to read_nonblock().
256 *
257 * This function tries to read at most \a bufsize bytes from the non-blocking
258 * file descriptor \a fd. If at least \p strlen(\a pattern) bytes have been
259 * received, the beginning of the received buffer is compared with \a pattern,
260 * ignoring case.
261 *
262 * \return Positive if \a pattern was received, negative on errors, zero if no data
263 * was available to read.
264 *
265 * \sa \ref read_nonblock(), \sa strncasecmp(3).
266 */
267 int read_pattern(int fd, const char *pattern, size_t bufsize, fd_set *rfds)
268 {
269 size_t n, len;
270 char *buf = para_malloc(bufsize + 1);
271 int ret = read_nonblock(fd, buf, bufsize, rfds, &n);
272
273 buf[n] = '\0';
274 if (ret < 0)
275 goto out;
276 ret = 0;
277 if (n == 0)
278 goto out;
279 ret = -E_READ_PATTERN;
280 len = strlen(pattern);
281 if (n < len)
282 goto out;
283 if (strncasecmp(buf, pattern, len) != 0)
284 goto out;
285 ret = 1;
286 out:
287 if (ret < 0) {
288 PARA_NOTICE_LOG("%s\n", para_strerror(-ret));
289 PARA_NOTICE_LOG("recvd %zu bytes: %s\n", n, buf);
290 }
291 free(buf);
292 return ret;
293 }
294
295 /**
296 * Check whether a file exists.
297 *
298 * \param fn The file name.
299 *
300 * \return Non-zero iff file exists.
301 */
302 int file_exists(const char *fn)
303 {
304 struct stat statbuf;
305
306 return !stat(fn, &statbuf);
307 }
308
309 /**
310 * Paraslash's wrapper for select(2).
311 *
312 * It calls select(2) (with no exceptfds) and starts over if select() was
313 * interrupted by a signal.
314 *
315 * \param n The highest-numbered descriptor in any of the two sets, plus 1.
316 * \param readfds fds that should be checked for readability.
317 * \param writefds fds that should be checked for writablility.
318 * \param timeout_tv upper bound on the amount of time elapsed before select()
319 * returns.
320 *
321 * \return The return value of the underlying select() call on success, the
322 * negative system error code on errors.
323 *
324 * All arguments are passed verbatim to select(2).
325 * \sa select(2) select_tut(2).
326 */
327 int para_select(int n, fd_set *readfds, fd_set *writefds,
328 struct timeval *timeout_tv)
329 {
330 int ret;
331 do
332 ret = select(n, readfds, writefds, NULL, timeout_tv);
333 while (ret < 0 && errno == EINTR);
334 if (ret < 0)
335 return -ERRNO_TO_PARA_ERROR(errno);
336 return ret;
337 }
338
339 /**
340 * Set a file descriptor to blocking mode.
341 *
342 * \param fd The file descriptor.
343 *
344 * \return Standard.
345 */
346 __must_check int mark_fd_blocking(int fd)
347 {
348 int flags = fcntl(fd, F_GETFL);
349 if (flags < 0)
350 return -ERRNO_TO_PARA_ERROR(errno);
351 flags = fcntl(fd, F_SETFL, ((long)flags) & ~O_NONBLOCK);
352 if (flags < 0)
353 return -ERRNO_TO_PARA_ERROR(errno);
354 return 1;
355 }
356
357 /**
358 * Set a file descriptor to non-blocking mode.
359 *
360 * \param fd The file descriptor.
361 *
362 * \return Standard.
363 */
364 __must_check int mark_fd_nonblocking(int fd)
365 {
366 int flags = fcntl(fd, F_GETFL);
367 if (flags < 0)
368 return -ERRNO_TO_PARA_ERROR(errno);
369 flags = fcntl(fd, F_SETFL, ((long)flags) | O_NONBLOCK);
370 if (flags < 0)
371 return -ERRNO_TO_PARA_ERROR(errno);
372 return 1;
373 }
374
375 /**
376 * Set a file descriptor in a fd_set.
377 *
378 * \param fd The file descriptor to be set.
379 * \param fds The file descriptor set.
380 * \param max_fileno Highest-numbered file descriptor.
381 *
382 * This wrapper for FD_SET() passes its first two arguments to \p FD_SET. Upon
383 * return, \a max_fileno contains the maximum of the old_value and \a fd.
384 *
385 * \sa para_select.
386 */
387 void para_fd_set(int fd, fd_set *fds, int *max_fileno)
388 {
389 assert(fd >= 0 && fd < FD_SETSIZE);
390 #if 0
391 {
392 int flags = fcntl(fd, F_GETFL);
393 if (!(flags & O_NONBLOCK)) {
394 PARA_EMERG_LOG("fd %d is a blocking file descriptor\n", fd);
395 exit(EXIT_FAILURE);
396 }
397 }
398 #endif
399 FD_SET(fd, fds);
400 *max_fileno = PARA_MAX(*max_fileno, fd);
401 }
402
403 /**
404 * Paraslash's wrapper for fgets(3).
405 *
406 * \param line Pointer to the buffer to store the line.
407 * \param size The size of the buffer given by \a line.
408 * \param f The stream to read from.
409 *
410 * \return Unlike the standard fgets() function, an integer value
411 * is returned. On success, this function returns 1. On errors, -E_FGETS
412 * is returned. A zero return value indicates an end of file condition.
413 */
414 __must_check int para_fgets(char *line, int size, FILE *f)
415 {
416 again:
417 if (fgets(line, size, f))
418 return 1;
419 if (feof(f))
420 return 0;
421 if (!ferror(f))
422 return -E_FGETS;
423 if (errno != EINTR) {
424 PARA_ERROR_LOG("%s\n", strerror(errno));
425 return -E_FGETS;
426 }
427 clearerr(f);
428 goto again;
429 }
430
431 /**
432 * Paraslash's wrapper for mmap.
433 *
434 * \param length Number of bytes to mmap.
435 * \param prot Either PROT_NONE or the bitwise OR of one or more of
436 * PROT_EXEC PROT_READ PROT_WRITE.
437 * \param flags Exactly one of MAP_SHARED and MAP_PRIVATE.
438 * \param fd The file to mmap from.
439 * \param offset Mmap start.
440 * \param map Result pointer.
441 *
442 * \return Standard.
443 *
444 * \sa mmap(2).
445 */
446 int para_mmap(size_t length, int prot, int flags, int fd, off_t offset,
447 void *map)
448 {
449 void **m = map;
450
451 errno = EINVAL;
452 if (!length)
453 goto err;
454 *m = mmap(NULL, length, prot, flags, fd, offset);
455 if (*m != MAP_FAILED)
456 return 1;
457 err:
458 *m = NULL;
459 return -ERRNO_TO_PARA_ERROR(errno);
460 }
461
462 /**
463 * Wrapper for the open(2) system call.
464 *
465 * \param path The filename.
466 * \param flags The usual open(2) flags.
467 * \param mode Specifies the permissions to use.
468 *
469 * The mode parameter must be specified when O_CREAT is in the flags, and is
470 * ignored otherwise.
471 *
472 * \return The file descriptor on success, negative on errors.
473 *
474 * \sa open(2).
475 */
476 int para_open(const char *path, int flags, mode_t mode)
477 {
478 int ret = open(path, flags, mode);
479
480 if (ret >= 0)
481 return ret;
482 return -ERRNO_TO_PARA_ERROR(errno);
483 }
484
485 /**
486 * Wrapper for chdir(2).
487 *
488 * \param path The specified directory.
489 *
490 * \return Standard.
491 */
492 int para_chdir(const char *path)
493 {
494 int ret = chdir(path);
495
496 if (ret >= 0)
497 return 1;
498 return -ERRNO_TO_PARA_ERROR(errno);
499 }
500
501 /**
502 * Save the cwd and open a given directory.
503 *
504 * \param dirname Path to the directory to open.
505 * \param dir Result pointer.
506 * \param cwd File descriptor of the current working directory.
507 *
508 * \return Standard.
509 *
510 * Opening the current directory (".") and calling fchdir() to return is
511 * usually faster and more reliable than saving cwd in some buffer and calling
512 * chdir() afterwards.
513 *
514 * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
515 * stored in \a cwd. If the function returns success, and \a cwd is not \p
516 * NULL, the caller must close this file descriptor (probably after calling
517 * fchdir(*cwd)).
518 *
519 * On errors, the function undos everything, so the caller needs neither close
520 * any files, nor change back to the original working directory.
521 *
522 * \sa getcwd(3).
523 *
524 */
525 static int para_opendir(const char *dirname, DIR **dir, int *cwd)
526 {
527 int ret;
528
529 if (cwd) {
530 ret = para_open(".", O_RDONLY, 0);
531 if (ret < 0)
532 return ret;
533 *cwd = ret;
534 }
535 ret = para_chdir(dirname);
536 if (ret < 0)
537 goto close_cwd;
538 *dir = opendir(".");
539 if (*dir)
540 return 1;
541 ret = -ERRNO_TO_PARA_ERROR(errno);
542 /* Ignore return value of fchdir() and close(). We're busted anyway. */
543 if (cwd) {
544 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
545 }
546 close_cwd:
547 if (cwd)
548 close(*cwd);
549 return ret;
550 }
551
552 /**
553 * A wrapper for fchdir().
554 *
555 * \param fd An open file descriptor.
556 *
557 * \return Standard.
558 */
559 static int para_fchdir(int fd)
560 {
561 if (fchdir(fd) < 0)
562 return -ERRNO_TO_PARA_ERROR(errno);
563 return 1;
564 }
565
566 /**
567 * A wrapper for mkdir(2).
568 *
569 * \param path Name of the directory to create.
570 * \param mode The permissions to use.
571 *
572 * \return Standard.
573 */
574 int para_mkdir(const char *path, mode_t mode)
575 {
576 if (!mkdir(path, mode))
577 return 1;
578 return -ERRNO_TO_PARA_ERROR(errno);
579 }
580
581 /**
582 * Open a file and map it into memory.
583 *
584 * \param path Name of the regular file to map.
585 * \param open_mode Either \p O_RDONLY or \p O_RDWR.
586 * \param map On success, the mapping is returned here.
587 * \param size size of the mapping.
588 * \param fd_ptr The file descriptor of the mapping.
589 *
590 * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
591 * open call is closed after mmap(). Otherwise the file is kept open and the
592 * file descriptor is returned in \a fd_ptr.
593 *
594 * \return Standard.
595 *
596 * \sa para_open(), mmap(2).
597 */
598 int mmap_full_file(const char *path, int open_mode, void **map,
599 size_t *size, int *fd_ptr)
600 {
601 int fd, ret, mmap_prot, mmap_flags;
602 struct stat file_status;
603
604 if (open_mode == O_RDONLY) {
605 mmap_prot = PROT_READ;
606 mmap_flags = MAP_PRIVATE;
607 } else {
608 mmap_prot = PROT_READ | PROT_WRITE;
609 mmap_flags = MAP_SHARED;
610 }
611 ret = para_open(path, open_mode, 0);
612 if (ret < 0)
613 return ret;
614 fd = ret;
615 if (fstat(fd, &file_status) < 0) {
616 ret = -ERRNO_TO_PARA_ERROR(errno);
617 goto out;
618 }
619 *size = file_status.st_size;
620 /*
621 * If the file is empty, *size is zero and mmap() would return EINVAL
622 * (Invalid argument). This error is common enough to spend an extra
623 * error code which explicitly states the problem.
624 */
625 ret = -E_EMPTY;
626 if (*size == 0)
627 goto out;
628 /*
629 * If fd refers to a directory, mmap() returns ENODEV (No such device),
630 * at least on Linux. "Is a directory" seems to be more to the point.
631 */
632 ret = -ERRNO_TO_PARA_ERROR(EISDIR);
633 if (S_ISDIR(file_status.st_mode))
634 goto out;
635
636 ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
637 out:
638 if (ret < 0 || !fd_ptr)
639 close(fd);
640 else
641 *fd_ptr = fd;
642 return ret;
643 }
644
645 /**
646 * A wrapper for munmap(2).
647 *
648 * \param start The start address of the memory mapping.
649 * \param length The size of the mapping.
650 *
651 * \return Standard.
652 *
653 * \sa munmap(2), mmap_full_file().
654 */
655 int para_munmap(void *start, size_t length)
656 {
657 int err;
658
659 if (!start)
660 return 0;
661 if (munmap(start, length) >= 0)
662 return 1;
663 err = errno;
664 PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
665 strerror(err));
666 return -ERRNO_TO_PARA_ERROR(err);
667 }
668
669 /**
670 * Check a file descriptor for writability.
671 *
672 * \param fd The file descriptor.
673 *
674 * \return positive if fd is ready for writing, zero if it isn't, negative if
675 * an error occurred.
676 */
677
678 int write_ok(int fd)
679 {
680 struct timeval tv;
681 fd_set wfds;
682
683 FD_ZERO(&wfds);
684 FD_SET(fd, &wfds);
685 tv.tv_sec = 0;
686 tv.tv_usec = 0;
687 return para_select(fd + 1, NULL, &wfds, &tv);
688 }
689
690 /**
691 * Ensure that file descriptors 0, 1, and 2 are valid.
692 *
693 * Common approach that opens /dev/null until it gets a file descriptor greater
694 * than two.
695 *
696 * \sa okir's Black Hats Manual.
697 */
698 void valid_fd_012(void)
699 {
700 while (1) {
701 int fd = open("/dev/null", O_RDWR);
702 if (fd < 0)
703 exit(EXIT_FAILURE);
704 if (fd > 2) {
705 close(fd);
706 break;
707 }
708 }
709 }
710
711 /**
712 * Traverse the given directory recursively.
713 *
714 * \param dirname The directory to traverse.
715 * \param func The function to call for each entry.
716 * \param private_data Pointer to an arbitrary data structure.
717 *
718 * For each regular file under \a dirname, the supplied function \a func is
719 * called. The full path of the regular file and the \a private_data pointer
720 * are passed to \a func. Directories for which the calling process has no
721 * permissions to change to are silently ignored.
722 *
723 * \return Standard.
724 */
725 int for_each_file_in_dir(const char *dirname,
726 int (*func)(const char *, void *), void *private_data)
727 {
728 DIR *dir;
729 struct dirent *entry;
730 int cwd_fd, ret2, ret = para_opendir(dirname, &dir, &cwd_fd);
731
732 if (ret < 0)
733 return ret == -ERRNO_TO_PARA_ERROR(EACCES)? 1 : ret;
734 /* scan cwd recursively */
735 while ((entry = readdir(dir))) {
736 mode_t m;
737 char *tmp;
738 struct stat s;
739
740 if (!strcmp(entry->d_name, "."))
741 continue;
742 if (!strcmp(entry->d_name, ".."))
743 continue;
744 if (lstat(entry->d_name, &s) == -1)
745 continue;
746 m = s.st_mode;
747 if (!S_ISREG(m) && !S_ISDIR(m))
748 continue;
749 tmp = make_message("%s/%s", dirname, entry->d_name);
750 if (!S_ISDIR(m)) {
751 ret = func(tmp, private_data);
752 free(tmp);
753 if (ret < 0)
754 goto out;
755 continue;
756 }
757 /* directory */
758 ret = for_each_file_in_dir(tmp, func, private_data);
759 free(tmp);
760 if (ret < 0)
761 goto out;
762 }
763 ret = 1;
764 out:
765 closedir(dir);
766 ret2 = para_fchdir(cwd_fd);
767 if (ret2 < 0 && ret >= 0)
768 ret = ret2;
769 close(cwd_fd);
770 return ret;
771 }