1 /* utimecmp.c -- compare file time stamps
3 Copyright (C) 2004-2007, 2009-2010 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert. */
33 #include "stat-time.h"
39 # define MAX(a, b) ((a) > (b) ? (a) : (b))
42 #define BILLION (1000 * 1000 * 1000)
44 /* Best possible resolution that utimens can set and stat can return,
45 due to system-call limitations. It must be a power of 10 that is
46 no greater than 1 billion. */
48 enum { SYSCALL_RESOLUTION = 1 };
49 #elif ((HAVE_FUTIMESAT || HAVE_WORKING_UTIMES) \
50 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
51 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
52 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
53 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
54 || defined HAVE_STRUCT_STAT_ST_SPARE1))
55 enum { SYSCALL_RESOLUTION = 1000 };
57 enum { SYSCALL_RESOLUTION = BILLION };
60 /* Describe a file system and its time stamp resolution in nanoseconds. */
63 /* Device number of file system. */
66 /* An upper bound on the time stamp resolution of this file system,
67 ignoring any resolution that cannot be set via utimens. It is
68 represented by an integer count of nanoseconds. It must be
69 either 2 billion, or a power of 10 that is no greater than a
70 billion and is no less than SYSCALL_RESOLUTION. */
73 /* True if RESOLUTION is known to be exact, and is not merely an
74 upper bound on the true resolution. */
78 /* Hash some device info. */
80 dev_info_hash (void const *x, size_t table_size)
82 struct fs_res const *p = x;
84 /* Beware signed arithmetic gotchas. */
85 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
87 uintmax_t dev = p->dev;
88 return dev % table_size;
91 return p->dev % table_size;
94 /* Compare two dev_info structs. */
96 dev_info_compare (void const *x, void const *y)
98 struct fs_res const *a = x;
99 struct fs_res const *b = y;
100 return a->dev == b->dev;
103 /* Return -1, 0, 1 based on whether the destination file (with name
104 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
105 as SRC_STAT, or newer than SRC_STAT, respectively.
107 DST_NAME may be NULL if OPTIONS is 0.
109 If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
110 converted to the destination's timestamp resolution as filtered through
111 utimens. In this case, return -2 if the exact answer cannot be
112 determined; this can happen only if the time stamps are very close and
113 there is some trouble accessing the file system (e.g., the user does not
114 have permission to futz with the destination's time stamps). */
117 utimecmp (char const *dst_name,
118 struct stat const *dst_stat,
119 struct stat const *src_stat,
122 /* Things to watch out for:
124 The code uses a static hash table internally and is not safe in the
125 presence of signals, multiple threads, etc.
127 int and long int might be 32 bits. Many of the calculations store
128 numbers up to 2 billion, and multiply by 10; they have to avoid
129 multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
131 time_t might be unsigned. */
133 verify (TYPE_IS_INTEGER (time_t));
134 verify (TYPE_TWOS_COMPLEMENT (int));
136 /* Destination and source time stamps. */
137 time_t dst_s = dst_stat->st_mtime;
138 time_t src_s = src_stat->st_mtime;
139 int dst_ns = get_stat_mtime_ns (dst_stat);
140 int src_ns = get_stat_mtime_ns (src_stat);
142 if (options & UTIMECMP_TRUNCATE_SOURCE)
144 /* Look up the time stamp resolution for the destination device. */
146 /* Hash table for devices. */
147 static Hash_table *ht;
149 /* Information about the destination file system. */
150 static struct fs_res *new_dst_res;
151 struct fs_res *dst_res;
153 /* Time stamp resolution in nanoseconds. */
156 /* Quick exit, if possible. Since the worst resolution is 2
157 seconds, anything that differs by more than that does not
158 needs source truncation. */
159 if (dst_s == src_s && dst_ns == src_ns)
161 if (dst_s <= src_s - 2)
163 if (src_s <= dst_s - 2)
167 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
170 new_dst_res = xmalloc (sizeof *new_dst_res);
171 new_dst_res->resolution = 2 * BILLION;
172 new_dst_res->exact = false;
174 new_dst_res->dev = dst_stat->st_dev;
175 dst_res = hash_insert (ht, new_dst_res);
179 if (dst_res == new_dst_res)
181 /* NEW_DST_RES is now in use in the hash table, so allocate a
182 new entry next time. */
186 res = dst_res->resolution;
188 #ifdef _PC_TIMESTAMP_RESOLUTION
189 /* If the system will tell us the resolution, we're set! */
190 if (! dst_res->exact)
192 res = pathconf (dst_name, _PC_TIMESTAMP_RESOLUTION);
195 dst_res->resolution = res;
196 dst_res->exact = true;
201 if (! dst_res->exact)
203 /* This file system's resolution is not known exactly.
204 Deduce it, and store the result in the hash table. */
206 time_t dst_a_s = dst_stat->st_atime;
207 time_t dst_c_s = dst_stat->st_ctime;
208 time_t dst_m_s = dst_s;
209 int dst_a_ns = get_stat_atime_ns (dst_stat);
210 int dst_c_ns = get_stat_ctime_ns (dst_stat);
211 int dst_m_ns = dst_ns;
213 /* Set RES to an upper bound on the file system resolution
214 (after truncation due to SYSCALL_RESOLUTION) by inspecting
215 the atime, ctime and mtime of the existing destination.
216 We don't know of any file system that stores atime or
217 ctime with a higher precision than mtime, so it's valid to
220 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
222 if (SYSCALL_RESOLUTION == BILLION)
224 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
233 /* Write it this way to avoid mistaken GCC warning
234 about integer overflow in constant expression. */
235 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
237 if ((a % SR10 | c % SR10 | m % SR10) != 0)
238 res = SYSCALL_RESOLUTION;
240 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
241 (res < dst_res->resolution
242 && (a % 10 | c % 10 | m % 10) == 0);
243 res *= 10, a /= 10, c /= 10, m /= 10)
252 dst_res->resolution = res;
255 if (SYSCALL_RESOLUTION < res)
257 struct timespec timespec[2];
258 struct stat dst_status;
260 /* Ignore source time stamp information that must necessarily
261 be lost when filtered through utimens. */
262 src_ns -= src_ns % SYSCALL_RESOLUTION;
264 /* If the time stamps disagree widely enough, there's no need
265 to interrogate the file system to deduce the exact time
266 stamp resolution; return the answer directly. */
268 time_t s = src_s & ~ (res == 2 * BILLION);
269 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
272 || (dst_s == s && dst_ns < src_ns - src_ns % res))
276 /* Determine the actual time stamp resolution for the
277 destination file system (after truncation due to
278 SYSCALL_RESOLUTION) by setting the access time stamp of the
279 destination to the existing access time, except with
280 trailing nonzero digits. */
282 timespec[0].tv_sec = dst_a_s;
283 timespec[0].tv_nsec = dst_a_ns;
284 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
285 timespec[1].tv_nsec = dst_m_ns + res / 9;
287 /* Set the modification time. But don't try to set the
288 modification time of symbolic links; on many hosts this sets
289 the time of the pointed-to file. */
290 if ((S_ISLNK (dst_stat->st_mode)
291 ? lutimens (dst_name, timespec)
292 : utimens (dst_name, timespec)) != 0)
295 /* Read the modification time that was set. */
297 int stat_result = (S_ISLNK (dst_stat->st_mode)
298 ? lstat (dst_name, &dst_status)
299 : stat (dst_name, &dst_status));
302 | (dst_status.st_mtime ^ dst_m_s)
303 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
305 /* The modification time changed, or we can't tell whether
306 it changed. Change it back as best we can. */
307 timespec[1].tv_sec = dst_m_s;
308 timespec[1].tv_nsec = dst_m_ns;
309 if (S_ISLNK (dst_stat->st_mode))
310 lutimens (dst_name, timespec);
312 utimens (dst_name, timespec);
315 if (stat_result != 0)
319 /* Determine the exact resolution from the modification time
320 that was read back. */
323 int a = (BILLION * (dst_status.st_mtime & 1)
324 + get_stat_mtime_ns (&dst_status));
326 res = SYSCALL_RESOLUTION;
328 for (a /= res; a % 10 != 0; a /= 10)
342 dst_res->resolution = res;
343 dst_res->exact = true;
346 /* Truncate the source's time stamp according to the resolution. */
347 src_s &= ~ (res == 2 * BILLION);
348 src_ns -= src_ns % res;
351 /* Compare the time stamps and return -1, 0, 1 accordingly. */
352 return (dst_s < src_s ? -1
354 : dst_ns < src_ns ? -1