前回まで自作のしょぼいtruncateを作ってましたが、本物のtruncateのソースを見て答え合わせしてみます。
※truncateのソースは、全文を記事の最後に載せています。
まずオプション解析。getopt_longを使ってます。まあそうでしょう。
231 while ((c = getopt_long (argc, argv, "cor:s:", longopts, NULL)) != -1)
232 {
233 switch (c)
argvとargcはオプション解析後に、調整して使うと、プログラムが分かりやすくなります。
302 argv += optind; 303 argc -= optind;
やはりstatを使ってるんですね。
333 if (ref_file)
334 {
335 struct stat sb;
336 off_t file_size = -1;
337 if (stat (ref_file, &sb) != 0)
338 die (EXIT_FAILURE, errno, _("cannot stat %s"), quoteaf (ref_file));
ファイルオープンは、fopenじゃなくて、大元のopen使ってます。statもopenもカーネルのシステムコールです。
339 if (usable_st_size (&sb))
340 file_size = sb.st_size;
341 else
342 {
343 int ref_fd = open (ref_file, O_RDONLY);
複数ファイルの処理です。369行目なかなかエレガントです。普段try~catchに慣れてしまうと、エラー処理ってどう書くのか忘れがちです。このソースを見ると初心を思い出してまだまだ勉強せねば、と思います。
369 while ((fname = *argv++) != NULL)
370 {
371 if ((fd = open (fname, oflags, MODE_RW_UGO)) == -1)
372 {
373 /* 'truncate -s0 -c no-such-file' shouldn't gen error
374 'truncate -s0 no-such-dir/file' should gen ENOENT error
375 'truncate -s0 no-such-dir/' should gen EISDIR error
376 'truncate -s0 .' should gen EISDIR error */
377 if (!(no_create && errno == ENOENT))
378 {
379 error (0, errno, _("cannot open %s for writing"),
380 quoteaf (fname));
381 errors = true;
382 }
383 continue;
384 }
気になる切り詰め処理は、do_ftruncateという関数になってました。中身も後で見てみます。最後はファイルのclose処理です。openとは違って != 0でエラー判定していますが、openにしてもcloseにしてもエラーは-1が返ります。謎が深まる。
387 if (fd != -1)
388 {
389 errors |= !do_ftruncate (fd, fname, size, rsize, rel_mode);
390 if (close (fd) != 0)
391 {
392 error (0, errno, _("failed to close %s"), quoteaf (fname));
393 errors = true;
394 }
395 }
396 }
397
398 return errors ? EXIT_FAILURE : EXIT_SUCCESS;
399 }
さて、do_ftruncateの中身を見ていきます。
105 static bool
106 do_ftruncate (int fd, char const *fname, off_t ssize, off_t rsize,
107 rel_mode_t rel_mode)
108 {
なんと、システムコールftruncate呼ぶんですね。
201 if (ftruncate (fd, nsize) == -1) /* note updates mtime & ctime */
202 {
203 error (0, errno,
204 _("failed to truncate %s at %" PRIdMAX " bytes"), quoteaf (fname),
205 (intmax_t) nsize);
206 return false;
207 }
man 2 ftruncateで確認。
TRUNCATE(2) Linux Programmer's Manual TRUNCATE(2)
名前
truncate, ftruncate - 指定した長さにファイルを切り詰める
書式
#include <unistd.h>
#include <sys/types.h>
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
これを知っていれば、自作truncateもこれを使ってることと思います。
結局ライブラリではなく、システムコールをするのかあ。
今まで見てきたtruncateの全文です。
takk@deb9:~/src/coreutils-8.26/src$ cat -n truncate.c
1 /* truncate -- truncate or extend the length of files.
2 Copyright (C) 2008-2016 Free Software Foundation, Inc.
3
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation, either version 3 of the License, or
7 (at your option) any later version.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
16
17 /* Written by Padraig Brady
18
19 This is backwards compatible with the FreeBSD utility, but is more
20 flexible wrt the size specifications and the use of long options,
21 to better fit the "GNU" environment. */
22
23 #include <config.h> /* sets _FILE_OFFSET_BITS=64 etc. */
24 #include <stdio.h>
25 #include <getopt.h>
26 #include <sys/types.h>
27
28 #include "system.h"
29 #include "die.h"
30 #include "error.h"
31 #include "quote.h"
32 #include "stat-size.h"
33 #include "xdectoint.h"
34
35 /* The official name of this program (e.g., no 'g' prefix). */
36 #define PROGRAM_NAME "truncate"
37
38 #define AUTHORS proper_name ("Padraig Brady")
39
40 /* (-c) If true, don't create if not already there */
41 static bool no_create;
42
43 /* (-o) If true, --size refers to blocks not bytes */
44 static bool block_mode;
45
46 /* (-r) Reference file to use size from */
47 static char const *ref_file;
48
49 static struct option const longopts[] =
50 {
51 {"no-create", no_argument, NULL, 'c'},
52 {"io-blocks", no_argument, NULL, 'o'},
53 {"reference", required_argument, NULL, 'r'},
54 {"size", required_argument, NULL, 's'},
55 {GETOPT_HELP_OPTION_DECL},
56 {GETOPT_VERSION_OPTION_DECL},
57 {NULL, 0, NULL, 0}
58 };
59
60 typedef enum
61 { rm_abs = 0, rm_rel, rm_min, rm_max, rm_rdn, rm_rup } rel_mode_t;
62
63 void
64 usage (int status)
65 {
66 if (status != EXIT_SUCCESS)
67 emit_try_help ();
68 else
69 {
70 printf (_("Usage: %s OPTION... FILE...\n"), program_name);
71 fputs (_("\
72 Shrink or extend the size of each FILE to the specified size\n\
73 \n\
74 A FILE argument that does not exist is created.\n\
75 \n\
76 If a FILE is larger than the specified size, the extra data is lost.\n\
77 If a FILE is shorter, it is extended and the extended part (hole)\n\
78 reads as zero bytes.\n\
79 "), stdout);
80
81 emit_mandatory_arg_note ();
82
83 fputs (_("\
84 -c, --no-create do not create any files\n\
85 "), stdout);
86 fputs (_("\
87 -o, --io-blocks treat SIZE as number of IO blocks instead of bytes\n\
88 "), stdout);
89 fputs (_("\
90 -r, --reference=RFILE base size on RFILE\n\
91 -s, --size=SIZE set or adjust the file size by SIZE bytes\n"), stdout);
92 fputs (HELP_OPTION_DESCRIPTION, stdout);
93 fputs (VERSION_OPTION_DESCRIPTION, stdout);
94 emit_size_note ();
95 fputs (_("\n\
96 SIZE may also be prefixed by one of the following modifying characters:\n\
97 '+' extend by, '-' reduce by, '<' at most, '>' at least,\n\
98 '/' round down to multiple of, '%' round up to multiple of.\n"), stdout);
99 emit_ancillary_info (PROGRAM_NAME);
100 }
101 exit (status);
102 }
103
104 /* return true on success, false on error. */
105 static bool
106 do_ftruncate (int fd, char const *fname, off_t ssize, off_t rsize,
107 rel_mode_t rel_mode)
108 {
109 struct stat sb;
110 off_t nsize;
111
112 if ((block_mode || (rel_mode && rsize < 0)) && fstat (fd, &sb) != 0)
113 {
114 error (0, errno, _("cannot fstat %s"), quoteaf (fname));
115 return false;
116 }
117 if (block_mode)
118 {
119 off_t const blksize = ST_BLKSIZE (sb);
120 if (ssize < OFF_T_MIN / blksize || ssize > OFF_T_MAX / blksize)
121 {
122 error (0, 0,
123 _("overflow in %" PRIdMAX
124 " * %" PRIdMAX " byte blocks for file %s"),
125 (intmax_t) ssize, (intmax_t) blksize,
126 quoteaf (fname));
127 return false;
128 }
129 ssize *= blksize;
130 }
131 if (rel_mode)
132 {
133 uintmax_t fsize;
134
135 if (0 <= rsize)
136 fsize = rsize;
137 else
138 {
139 off_t file_size;
140 if (usable_st_size (&sb))
141 {
142 file_size = sb.st_size;
143 if (file_size < 0)
144 {
145 /* Sanity check. Overflow is the only reason I can think
146 this would ever go negative. */
147 error (0, 0, _("%s has unusable, apparently negative size"),
148 quoteaf (fname));
149 return false;
150 }
151 }
152 else
153 {
154 file_size = lseek (fd, 0, SEEK_END);
155 if (file_size < 0)
156 {
157 error (0, errno, _("cannot get the size of %s"),
158 quoteaf (fname));
159 return false;
160 }
161 }
162 fsize = file_size;
163 }
164
165 if (rel_mode == rm_min)
166 nsize = MAX (fsize, (uintmax_t) ssize);
167 else if (rel_mode == rm_max)
168 nsize = MIN (fsize, (uintmax_t) ssize);
169 else if (rel_mode == rm_rdn)
170 /* 0..ssize-1 -> 0 */
171 nsize = (fsize / ssize) * ssize;
172 else if (rel_mode == rm_rup)
173 /* 1..ssize -> ssize */
174 {
175 /* Here ssize>=1 && fsize>=0 */
176 uintmax_t const overflow = ((fsize + ssize - 1) / ssize) * ssize;
177 if (overflow > OFF_T_MAX)
178 {
179 error (0, 0, _("overflow rounding up size of file %s"),
180 quoteaf (fname));
181 return false;
182 }
183 nsize = overflow;
184 }
185 else
186 {
187 if (ssize > OFF_T_MAX - (off_t)fsize)
188 {
189 error (0, 0, _("overflow extending size of file %s"),
190 quoteaf (fname));
191 return false;
192 }
193 nsize = fsize + ssize;
194 }
195 }
196 else
197 nsize = ssize;
198 if (nsize < 0)
199 nsize = 0;
200
201 if (ftruncate (fd, nsize) == -1) /* note updates mtime & ctime */
202 {
203 error (0, errno,
204 _("failed to truncate %s at %" PRIdMAX " bytes"), quoteaf (fname),
205 (intmax_t) nsize);
206 return false;
207 }
208
209 return true;
210 }
211
212 int
213 main (int argc, char **argv)
214 {
215 bool got_size = false;
216 bool errors = false;
217 off_t size IF_LINT ( = 0);
218 off_t rsize = -1;
219 rel_mode_t rel_mode = rm_abs;
220 int c, fd = -1, oflags;
221 char const *fname;
222
223 initialize_main (&argc, &argv);
224 set_program_name (argv[0]);
225 setlocale (LC_ALL, "");
226 bindtextdomain (PACKAGE, LOCALEDIR);
227 textdomain (PACKAGE);
228
229 atexit (close_stdout);
230
231 while ((c = getopt_long (argc, argv, "cor:s:", longopts, NULL)) != -1)
232 {
233 switch (c)
234 {
235 case 'c':
236 no_create = true;
237 break;
238
239 case 'o':
240 block_mode = true;
241 break;
242
243 case 'r':
244 ref_file = optarg;
245 break;
246
247 case 's':
248 /* skip any whitespace */
249 while (isspace (to_uchar (*optarg)))
250 optarg++;
251 switch (*optarg)
252 {
253 case '<':
254 rel_mode = rm_max;
255 optarg++;
256 break;
257 case '>':
258 rel_mode = rm_min;
259 optarg++;
260 break;
261 case '/':
262 rel_mode = rm_rdn;
263 optarg++;
264 break;
265 case '%':
266 rel_mode = rm_rup;
267 optarg++;
268 break;
269 }
270 /* skip any whitespace */
271 while (isspace (to_uchar (*optarg)))
272 optarg++;
273 if (*optarg == '+' || *optarg == '-')
274 {
275 if (rel_mode)
276 {
277 error (0, 0, _("multiple relative modifiers specified"));
278 /* Note other combinations are flagged as invalid numbers */
279 usage (EXIT_FAILURE);
280 }
281 rel_mode = rm_rel;
282 }
283 /* Support dd BLOCK size suffixes + lowercase g,t,m for bsd compat.
284 Note we don't support dd's b=512, c=1, w=2 or 21x512MiB formats. */
285 size = xdectoimax (optarg, OFF_T_MIN, OFF_T_MAX, "EgGkKmMPtTYZ0",
286 _("Invalid number"), 0);
287 /* Rounding to multiple of 0 is nonsensical */
288 if ((rel_mode == rm_rup || rel_mode == rm_rdn) && size == 0)
289 die (EXIT_FAILURE, 0, _("division by zero"));
290 got_size = true;
291 break;
292
293 case_GETOPT_HELP_CHAR;
294
295 case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
296
297 default:
298 usage (EXIT_FAILURE);
299 }
300 }
301
302 argv += optind;
303 argc -= optind;
304
305 /* must specify either size or reference file */
306 if (!ref_file && !got_size)
307 {
308 error (0, 0, _("you must specify either %s or %s"),
309 quote_n (0, "--size"), quote_n (1, "--reference"));
310 usage (EXIT_FAILURE);
311 }
312 /* must specify a relative size with a reference file */
313 if (ref_file && got_size && !rel_mode)
314 {
315 error (0, 0, _("you must specify a relative %s with %s"),
316 quote_n (0, "--size"), quote_n (1, "--reference"));
317 usage (EXIT_FAILURE);
318 }
319 /* block_mode without size is not valid */
320 if (block_mode && !got_size)
321 {
322 error (0, 0, _("%s was specified but %s was not"),
323 quote_n (0, "--io-blocks"), quote_n (1, "--size"));
324 usage (EXIT_FAILURE);
325 }
326 /* must specify at least 1 file */
327 if (argc < 1)
328 {
329 error (0, 0, _("missing file operand"));
330 usage (EXIT_FAILURE);
331 }
332
333 if (ref_file)
334 {
335 struct stat sb;
336 off_t file_size = -1;
337 if (stat (ref_file, &sb) != 0)
338 die (EXIT_FAILURE, errno, _("cannot stat %s"), quoteaf (ref_file));
339 if (usable_st_size (&sb))
340 file_size = sb.st_size;
341 else
342 {
343 int ref_fd = open (ref_file, O_RDONLY);
344 if (0 <= ref_fd)
345 {
346 off_t file_end = lseek (ref_fd, 0, SEEK_END);
347 int saved_errno = errno;
348 close (ref_fd); /* ignore failure */
349 if (0 <= file_end)
350 file_size = file_end;
351 else
352 {
353 /* restore, in case close clobbered it. */
354 errno = saved_errno;
355 }
356 }
357 }
358 if (file_size < 0)
359 die (EXIT_FAILURE, errno, _("cannot get the size of %s"),
360 quoteaf (ref_file));
361 if (!got_size)
362 size = file_size;
363 else
364 rsize = file_size;
365 }
366
367 oflags = O_WRONLY | (no_create ? 0 : O_CREAT) | O_NONBLOCK;
368
369 while ((fname = *argv++) != NULL)
370 {
371 if ((fd = open (fname, oflags, MODE_RW_UGO)) == -1)
372 {
373 /* 'truncate -s0 -c no-such-file' shouldn't gen error
374 'truncate -s0 no-such-dir/file' should gen ENOENT error
375 'truncate -s0 no-such-dir/' should gen EISDIR error
376 'truncate -s0 .' should gen EISDIR error */
377 if (!(no_create && errno == ENOENT))
378 {
379 error (0, errno, _("cannot open %s for writing"),
380 quoteaf (fname));
381 errors = true;
382 }
383 continue;
384 }
385
386
387 if (fd != -1)
388 {
389 errors |= !do_ftruncate (fd, fname, size, rsize, rel_mode);
390 if (close (fd) != 0)
391 {
392 error (0, errno, _("failed to close %s"), quoteaf (fname));
393 errors = true;
394 }
395 }
396 }
397
398 return errors ? EXIT_FAILURE : EXIT_SUCCESS;
399 }
takk@deb9:~/src/coreutils-8.26/src$
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