1 /**
2 * @file text_mmap.c
3 *
4 * Map a text file, ensuring the text always has an ending NUL byte.
5 *
6 * @addtogroup autoopts
7 * @{
8 */
9 /*
10 * This file is part of AutoOpts, a companion to AutoGen.
11 * AutoOpts is free software.
12 * AutoOpts is Copyright (C) 1992-2015 by Bruce Korb - all rights reserved
13 *
14 * AutoOpts is available under any one of two licenses. The license
15 * in use must be one of these two and the choice is under the control
16 * of the user of the license.
17 *
18 * The GNU Lesser General Public License, version 3 or later
19 * See the files "COPYING.lgplv3" and "COPYING.gplv3"
20 *
21 * The Modified Berkeley Software Distribution License
22 * See the file "COPYING.mbsd"
23 *
24 * These files have the following sha256 sums:
25 *
26 * 8584710e9b04216a394078dc156b781d0b47e1729104d666658aecef8ee32e95 COPYING.gplv3
27 * 4379e7444a0e2ce2b12dd6f5a52a27a4d02d39d247901d3285c88cf0d37f477b COPYING.lgplv3
28 * 13aa749a5b0a454917a944ed8fffc530b784f5ead522b1aacaf4ec8aa55a6239 COPYING.mbsd
29 */
30 #if defined(HAVE_MMAP)
31 # ifndef MAP_ANONYMOUS
32 # ifdef MAP_ANON
33 # define MAP_ANONYMOUS MAP_ANON
34 # endif
35 # endif
36
37 # if ! defined(MAP_ANONYMOUS) && ! defined(HAVE_DEV_ZERO)
38 /*
39 * We must have either /dev/zero or anonymous mapping for
40 * this to work.
41 */
42 # undef HAVE_MMAP
43
44 # else
45 # ifdef _SC_PAGESIZE
46 # define GETPAGESIZE() sysconf(_SC_PAGESIZE)
47 # else
48 # define GETPAGESIZE() getpagesize()
49 # endif
50 # endif
51 #endif
52
53 /*
54 * Some weird systems require that a specifically invalid FD number
55 * get passed in as an argument value. Which value is that? Well,
56 * as everybody knows, if open(2) fails, it returns -1, so that must
57 * be the value. :)
58 */
59 #define AO_INVALID_FD -1
60
61 #define FILE_WRITABLE(_prt,_flg) \
62 ( (_prt & PROT_WRITE) \
63 && ((_flg & (MAP_SHARED|MAP_PRIVATE)) == MAP_SHARED))
64 #define MAP_FAILED_PTR (VOIDP(MAP_FAILED))
65
66 /**
67 * Load the contents of a text file. There are two separate implementations,
68 * depending up on whether mmap(3) is available.
69 *
70 * If not available, malloc the file length plus one byte. Read it in
71 * and NUL terminate.
72 *
73 * If available, first check to see if the text file size is a multiple of a
74 * page size. If it is, map the file size plus an extra page from either
75 * anonymous memory or from /dev/zero. Then map the file text on top of the
76 * first pages of the anonymous/zero pages. Otherwise, just map the file
77 * because there will be NUL bytes provided at the end.
78 *
79 * @param mapinfo a structure holding everything we need to know
80 * about the mapping.
81 *
82 * @param pzFile name of the file, for error reporting.
83 */
84 static void
load_text_file(tmap_info_t * mapinfo,char const * pzFile)85 load_text_file(tmap_info_t * mapinfo, char const * pzFile)
86 {
87 #if ! defined(HAVE_MMAP)
88 mapinfo->txt_data = AGALOC(mapinfo->txt_size+1, "file text");
89 if (mapinfo->txt_data == NULL) {
90 mapinfo->txt_errno = ENOMEM;
91 return;
92 }
93
94 {
95 size_t sz = mapinfo->txt_size;
96 char * pz = mapinfo->txt_data;
97
98 while (sz > 0) {
99 ssize_t rdct = read(mapinfo->txt_fd, pz, sz);
100 if (rdct <= 0) {
101 mapinfo->txt_errno = errno;
102 fserr_warn("libopts", "read", pzFile);
103 free(mapinfo->txt_data);
104 return;
105 }
106
107 pz += rdct;
108 sz -= rdct;
109 }
110
111 *pz = NUL;
112 }
113
114 mapinfo->txt_errno = 0;
115
116 #else /* HAVE mmap */
117 size_t const pgsz = (size_t)GETPAGESIZE();
118 void * map_addr = NULL;
119
120 (void)pzFile;
121
122 mapinfo->txt_full_size = (mapinfo->txt_size + pgsz) & ~(pgsz - 1);
123 if (mapinfo->txt_full_size == (mapinfo->txt_size + pgsz)) {
124 /*
125 * The text is a multiple of a page boundary. We must map an
126 * extra page so the text ends with a NUL.
127 */
128 #if defined(MAP_ANONYMOUS)
129 map_addr = mmap(NULL, mapinfo->txt_full_size, PROT_READ|PROT_WRITE,
130 MAP_ANONYMOUS|MAP_PRIVATE, AO_INVALID_FD, 0);
131 #else
132 mapinfo->txt_zero_fd = open("/dev/zero", O_RDONLY);
133
134 if (mapinfo->txt_zero_fd == AO_INVALID_FD) {
135 mapinfo->txt_errno = errno;
136 return;
137 }
138 map_addr = mmap(NULL, mapinfo->txt_full_size, PROT_READ|PROT_WRITE,
139 MAP_PRIVATE, mapinfo->txt_zero_fd, 0);
140 #endif
141 if (map_addr == MAP_FAILED_PTR) {
142 mapinfo->txt_errno = errno;
143 return;
144 }
145 mapinfo->txt_flags |= MAP_FIXED;
146 }
147
148 mapinfo->txt_data =
149 mmap(map_addr, mapinfo->txt_size, mapinfo->txt_prot,
150 mapinfo->txt_flags, mapinfo->txt_fd, 0);
151
152 if (mapinfo->txt_data == MAP_FAILED_PTR)
153 mapinfo->txt_errno = errno;
154 #endif /* HAVE_MMAP */
155 }
156
157 /**
158 * Make sure all the parameters are correct: we have a file name that
159 * is a text file that we can read.
160 *
161 * @param fname the text file to map
162 * @param prot the memory protections requested (read/write/etc.)
163 * @param flags mmap flags
164 * @param mapinfo a structure holding everything we need to know
165 * about the mapping.
166 */
167 static void
validate_mmap(char const * fname,int prot,int flags,tmap_info_t * mapinfo)168 validate_mmap(char const * fname, int prot, int flags, tmap_info_t * mapinfo)
169 {
170 memset(mapinfo, 0, sizeof(*mapinfo));
171 #if defined(HAVE_MMAP) && ! defined(MAP_ANONYMOUS)
172 mapinfo->txt_zero_fd = AO_INVALID_FD;
173 #endif
174 mapinfo->txt_fd = AO_INVALID_FD;
175 mapinfo->txt_prot = prot;
176 mapinfo->txt_flags = flags;
177
178 /*
179 * Map mmap flags and protections into open flags and do the open.
180 */
181 {
182 /*
183 * See if we will be updating the file. If we can alter the memory
184 * and if we share the data and we are *not* copy-on-writing the data,
185 * then our updates will show in the file, so we must open with
186 * write access.
187 */
188 int o_flag = FILE_WRITABLE(prot, flags) ? O_RDWR : O_RDONLY;
189
190 /*
191 * If you're not sharing the file and you are writing to it,
192 * then don't let anyone else have access to the file.
193 */
194 if (((flags & MAP_SHARED) == 0) && (prot & PROT_WRITE))
195 o_flag |= O_EXCL;
196
197 mapinfo->txt_fd = open(fname, o_flag);
198 if (mapinfo->txt_fd < 0) {
199 mapinfo->txt_errno = errno;
200 mapinfo->txt_fd = AO_INVALID_FD;
201 return;
202 }
203 }
204
205 /*
206 * Make sure we can stat the regular file. Save the file size.
207 */
208 {
209 struct stat sb;
210 if (fstat(mapinfo->txt_fd, &sb) != 0) {
211 mapinfo->txt_errno = errno;
212 close(mapinfo->txt_fd);
213 return;
214 }
215
216 if (! S_ISREG(sb.st_mode)) {
217 mapinfo->txt_errno = errno = EINVAL;
218 close(mapinfo->txt_fd);
219 return;
220 }
221
222 mapinfo->txt_size = (size_t)sb.st_size;
223 }
224
225 if (mapinfo->txt_fd == AO_INVALID_FD)
226 mapinfo->txt_errno = errno;
227 }
228
229 /**
230 * Close any files opened by the mapping.
231 *
232 * @param mi a structure holding everything we need to know about the map.
233 */
234 static void
close_mmap_files(tmap_info_t * mi)235 close_mmap_files(tmap_info_t * mi)
236 {
237 if (mi->txt_fd == AO_INVALID_FD)
238 return;
239
240 close(mi->txt_fd);
241 mi->txt_fd = AO_INVALID_FD;
242
243 #if defined(HAVE_MMAP) && ! defined(MAP_ANONYMOUS)
244 if (mi->txt_zero_fd == AO_INVALID_FD)
245 return;
246
247 close(mi->txt_zero_fd);
248 mi->txt_zero_fd = AO_INVALID_FD;
249 #endif
250 }
251
252 /*=export_func text_mmap
253 * private:
254 *
255 * what: map a text file with terminating NUL
256 *
257 * arg: char const *, pzFile, name of the file to map
258 * arg: int, prot, mmap protections (see mmap(2))
259 * arg: int, flags, mmap flags (see mmap(2))
260 * arg: tmap_info_t *, mapinfo, returned info about the mapping
261 *
262 * ret-type: void *
263 * ret-desc: The mmaped data address
264 *
265 * doc:
266 *
267 * This routine will mmap a file into memory ensuring that there is at least
268 * one @file{NUL} character following the file data. It will return the
269 * address where the file contents have been mapped into memory. If there is a
270 * problem, then it will return @code{MAP_FAILED} and set @code{errno}
271 * appropriately.
272 *
273 * The named file does not exist, @code{stat(2)} will set @code{errno} as it
274 * will. If the file is not a regular file, @code{errno} will be
275 * @code{EINVAL}. At that point, @code{open(2)} is attempted with the access
276 * bits set appropriately for the requested @code{mmap(2)} protections and flag
277 * bits. On failure, @code{errno} will be set according to the documentation
278 * for @code{open(2)}. If @code{mmap(2)} fails, @code{errno} will be set as
279 * that routine sets it. If @code{text_mmap} works to this point, a valid
280 * address will be returned, but there may still be ``issues''.
281 *
282 * If the file size is not an even multiple of the system page size, then
283 * @code{text_map} will return at this point and @code{errno} will be zero.
284 * Otherwise, an anonymous map is attempted. If not available, then an attempt
285 * is made to @code{mmap(2)} @file{/dev/zero}. If any of these fail, the
286 * address of the file's data is returned, bug @code{no} @file{NUL} characters
287 * are mapped after the end of the data.
288 *
289 * see: mmap(2), open(2), stat(2)
290 *
291 * err: Any error code issued by mmap(2), open(2), stat(2) is possible.
292 * Additionally, if the specified file is not a regular file, then
293 * errno will be set to @code{EINVAL}.
294 *
295 * example:
296 * #include <mylib.h>
297 * tmap_info_t mi;
298 * int no_nul;
299 * void * data = text_mmap("file", PROT_WRITE, MAP_PRIVATE, &mi);
300 * if (data == MAP_FAILED) return;
301 * no_nul = (mi.txt_size == mi.txt_full_size);
302 * << use the data >>
303 * text_munmap(&mi);
304 =*/
305 void *
text_mmap(char const * pzFile,int prot,int flags,tmap_info_t * mi)306 text_mmap(char const * pzFile, int prot, int flags, tmap_info_t * mi)
307 {
308 validate_mmap(pzFile, prot, flags, mi);
309 if (mi->txt_errno != 0)
310 return MAP_FAILED_PTR;
311
312 load_text_file(mi, pzFile);
313
314 if (mi->txt_errno == 0)
315 return mi->txt_data;
316
317 close_mmap_files(mi);
318
319 errno = mi->txt_errno;
320 mi->txt_data = MAP_FAILED_PTR;
321 return mi->txt_data;
322 }
323
324
325 /*=export_func text_munmap
326 * private:
327 *
328 * what: unmap the data mapped in by text_mmap
329 *
330 * arg: tmap_info_t *, mapinfo, info about the mapping
331 *
332 * ret-type: int
333 * ret-desc: -1 or 0. @code{errno} will have the error code.
334 *
335 * doc:
336 *
337 * This routine will unmap the data mapped in with @code{text_mmap} and close
338 * the associated file descriptors opened by that function.
339 *
340 * see: munmap(2), close(2)
341 *
342 * err: Any error code issued by munmap(2) or close(2) is possible.
343 =*/
344 int
text_munmap(tmap_info_t * mi)345 text_munmap(tmap_info_t * mi)
346 {
347 errno = 0;
348
349 #ifdef HAVE_MMAP
350 (void)munmap(mi->txt_data, mi->txt_full_size);
351
352 #else /* don't HAVE_MMAP */
353 /*
354 * IF the memory is writable *AND* it is not private (copy-on-write)
355 * *AND* the memory is "sharable" (seen by other processes)
356 * THEN rewrite the data. Emulate mmap visibility.
357 */
358 if ( FILE_WRITABLE(mi->txt_prot, mi->txt_flags)
359 && (lseek(mi->txt_fd, 0, SEEK_SET) >= 0) ) {
360 write(mi->txt_fd, mi->txt_data, mi->txt_size);
361 }
362
363 free(mi->txt_data);
364 #endif /* HAVE_MMAP */
365
366 mi->txt_errno = errno;
367 close_mmap_files(mi);
368
369 return mi->txt_errno;
370 }
371
372 /** @}
373 *
374 * Local Variables:
375 * mode: C
376 * c-file-style: "stroustrup"
377 * indent-tabs-mode: nil
378 * End:
379 * end of autoopts/text_mmap.c */
380