para_fd_set(): Replace check for invalid fds by an assert().
[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
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 *
229 * \return This function either returns a valid pointer to the mapped area
230 * or calls exit() on errors.
231 */
232 void *para_mmap(size_t length, int prot, int flags, int fd, off_t offset)
233 {
234 void *ret = mmap(NULL, length, prot, flags, fd, offset);
235 if (ret != MAP_FAILED)
236 return ret;
237 PARA_EMERG_LOG("mmap failed: %s\n", strerror(errno));
238 PARA_EMERG_LOG("length: %zu, flags: %d, fd: %d, offset: %zu\n",
239 length, flags, fd, (size_t)offset);
240 exit(EXIT_FAILURE);
241 }
242
243 /**
244 * Wrapper for the open(2) system call.
245 *
246 * \param path The filename.
247 * \param flags The usual open(2) flags.
248 * \param mode Specifies the permissions to use.
249 *
250 * The mode parameter must be specified when O_CREAT is in the flags, and is
251 * ignored otherwise.
252 *
253 * \return The file descriptor on success, negative on errors.
254 *
255 * \sa open(2).
256 */
257 int para_open(const char *path, int flags, mode_t mode)
258 {
259 int ret = open(path, flags, mode);
260
261 if (ret >= 0)
262 return ret;
263 return -ERRNO_TO_PARA_ERROR(errno);
264 }
265
266 /**
267 * Wrapper for chdir(2).
268 *
269 * \param path The specified directory.
270 *
271 * \return Standard.
272 */
273 int para_chdir(const char *path)
274 {
275 int ret = chdir(path);
276
277 if (ret >= 0)
278 return 1;
279 return -ERRNO_TO_PARA_ERROR(errno);
280 }
281
282 /**
283 * Save the cwd and open a given directory.
284 *
285 * \param dirname Path to the directory to open.
286 * \param dir Result pointer.
287 * \param cwd File descriptor of the current working directory.
288 *
289 * \return Standard.
290 *
291 * Opening the current directory (".") and calling fchdir() to return is
292 * usually faster and more reliable than saving cwd in some buffer and calling
293 * chdir() afterwards.
294 *
295 * If \a cwd is not \p NULL "." is opened and the resulting file descriptor is
296 * stored in \a cwd. If the function returns success, and \a cwd is not \p
297 * NULL, the caller must close this file descriptor (probably after calling
298 * fchdir(*cwd)).
299 *
300 * On errors, the function undos everything, so the caller needs neither close
301 * any files, nor change back to the original working directory.
302 *
303 * \sa getcwd(3).
304 *
305 */
306 int para_opendir(const char *dirname, DIR **dir, int *cwd)
307 {
308 int ret;
309
310 if (cwd) {
311 ret = para_open(".", O_RDONLY, 0);
312 if (ret < 0)
313 return ret;
314 *cwd = ret;
315 }
316 ret = para_chdir(dirname);
317 if (ret < 0)
318 goto close_cwd;
319 *dir = opendir(".");
320 if (*dir)
321 return 1;
322 ret = -ERRNO_TO_PARA_ERROR(errno);
323 /* Ignore return value of fchdir() and close(). We're busted anyway. */
324 if (cwd) {
325 int __a_unused ret2 = fchdir(*cwd); /* STFU, gcc */
326 }
327 close_cwd:
328 if (cwd)
329 close(*cwd);
330 return ret;
331 }
332
333 /**
334 * A wrapper for fchdir().
335 *
336 * \param fd An open file descriptor.
337 *
338 * \return Standard.
339 */
340 int para_fchdir(int fd)
341 {
342 if (fchdir(fd) < 0)
343 return -ERRNO_TO_PARA_ERROR(errno);
344 return 1;
345 }
346
347 /**
348 * A wrapper for mkdir(2).
349 *
350 * \param path Name of the directory to create.
351 * \param mode The permissions to use.
352 *
353 * \return Standard.
354 */
355 int para_mkdir(const char *path, mode_t mode)
356 {
357 if (!mkdir(path, mode))
358 return 1;
359 return -ERRNO_TO_PARA_ERROR(errno);
360 }
361
362 /**
363 * Open a file and map it into memory.
364 *
365 * \param path Name of the regular file to map.
366 * \param open_mode Either \p O_RDONLY or \p O_RDWR.
367 * \param map On success, the mapping is returned here.
368 * \param size size of the mapping.
369 * \param fd_ptr The file descriptor of the mapping.
370 *
371 * If \a fd_ptr is \p NULL, the file descriptor resulting from the underlying
372 * open call is closed after mmap(). Otherwise the file is kept open and the
373 * file descriptor is returned in \a fd_ptr.
374 *
375 * \return Standard.
376 *
377 * \sa para_open(), mmap(2).
378 */
379 int mmap_full_file(const char *path, int open_mode, void **map,
380 size_t *size, int *fd_ptr)
381 {
382 int fd, ret, mmap_prot, mmap_flags;
383 struct stat file_status;
384
385 if (open_mode == O_RDONLY) {
386 mmap_prot = PROT_READ;
387 mmap_flags = MAP_PRIVATE;
388 } else {
389 mmap_prot = PROT_READ | PROT_WRITE;
390 mmap_flags = MAP_SHARED;
391 }
392 ret = para_open(path, open_mode, 0);
393 if (ret < 0)
394 return ret;
395 fd = ret;
396 if (fstat(fd, &file_status) < 0) {
397 ret = -ERRNO_TO_PARA_ERROR(errno);
398 goto out;
399 }
400 *size = file_status.st_size;
401 ret = -E_EMPTY;
402 PARA_DEBUG_LOG("%s: size %zu\n", path, *size);
403 if (!*size)
404 goto out;
405 *map = mmap(NULL, *size, mmap_prot, mmap_flags, fd, 0);
406 if (*map == MAP_FAILED) {
407 *map = NULL;
408 ret = -E_MMAP;
409 goto out;
410 }
411 ret = 1;
412 out:
413 if (ret < 0 || !fd_ptr)
414 close(fd);
415 else
416 *fd_ptr = fd;
417 return ret;
418 }
419
420 /**
421 * A wrapper for munmap(2).
422 *
423 * \param start The start address of the memory mapping.
424 * \param length The size of the mapping.
425 *
426 * \return Positive on success, \p -E_MUNMAP on errors.
427 *
428 * \sa munmap(2), mmap_full_file().
429 */
430 int para_munmap(void *start, size_t length)
431 {
432 int err;
433 if (munmap(start, length) >= 0)
434 return 1;
435 err = errno;
436 PARA_ERROR_LOG("munmap (%p/%zu) failed: %s\n", start, length,
437 strerror(err));
438 return -ERRNO_TO_PARA_ERROR(err);
439 }
440
441 /**
442 * Check a file descriptor for writability.
443 *
444 * \param fd The file descriptor.
445 *
446 * \return positive if fd is ready for writing, zero if it isn't, negative if
447 * an error occurred.
448 */
449
450 int write_ok(int fd)
451 {
452 struct timeval tv = {0, 0};
453 fd_set wfds;
454 int ret;
455 again:
456 FD_ZERO(&wfds);
457 FD_SET(fd, &wfds);
458 tv.tv_sec = 0;
459 tv.tv_usec = 0;
460 ret = select(fd + 1, NULL, &wfds, NULL, &tv);
461 if (ret < 0 && errno == EINTR)
462 goto again;
463 return ret;
464 }
465
466 /**
467 * Ensure that file descriptors 0, 1, and 2 are valid.
468 *
469 * Common approach that opens /dev/null until it gets a file descriptor greater
470 * than two.
471 *
472 * \sa okir's Black Hats Manual.
473 */
474 void valid_fd_012(void)
475 {
476 while (1) {
477 int fd = open("/dev/null", O_RDWR);
478 if (fd < 0)
479 exit(EXIT_FAILURE);
480 if (fd > 2) {
481 close(fd);
482 break;
483 }
484 }
485 }