1 /* utimecmp.c -- compare file time stamps
3 Copyright (C) 2004-2007, 2009-2016 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"
38 # define MAX(a, b) ((a) > (b) ? (a) : (b))
41 #define BILLION (1000 * 1000 * 1000)
43 /* Best possible resolution that utimens can set and stat can return,
44 due to system-call limitations. It must be a power of 10 that is
45 no greater than 1 billion. */
47 enum { SYSCALL_RESOLUTION = 1 };
48 #elif ((HAVE_FUTIMESAT || HAVE_WORKING_UTIMES) \
49 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
50 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
51 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
52 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
53 || defined HAVE_STRUCT_STAT_ST_SPARE1))
54 enum { SYSCALL_RESOLUTION = 1000 };
56 enum { SYSCALL_RESOLUTION = BILLION };
59 /* Describe a file system and its time stamp resolution in nanoseconds. */
62 /* Device number of file system. */
65 /* An upper bound on the time stamp resolution of this file system,
66 ignoring any resolution that cannot be set via utimens. It is
67 represented by an integer count of nanoseconds. It must be
68 either 2 billion, or a power of 10 that is no greater than a
69 billion and is no less than SYSCALL_RESOLUTION. */
72 /* True if RESOLUTION is known to be exact, and is not merely an
73 upper bound on the true resolution. */
77 /* Hash some device info. */
79 dev_info_hash (void const *x, size_t table_size)
81 struct fs_res const *p = x;
83 /* Beware signed arithmetic gotchas. */
84 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
86 uintmax_t dev = p->dev;
87 return dev % table_size;
90 return p->dev % table_size;
93 /* Compare two dev_info structs. */
95 dev_info_compare (void const *x, void const *y)
97 struct fs_res const *a = x;
98 struct fs_res const *b = y;
99 return a->dev == b->dev;
102 /* Return -1, 0, 1 based on whether the destination file (with name
103 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
104 as SRC_STAT, or newer than SRC_STAT, respectively.
106 DST_NAME may be NULL if OPTIONS is 0.
108 If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
109 converted to the destination's timestamp resolution as filtered through
110 utimens. In this case, return -2 if the exact answer cannot be
111 determined; this can happen only if the time stamps are very close and
112 there is some trouble accessing the file system (e.g., the user does not
113 have permission to futz with the destination's time stamps). */
116 utimecmp (char const *dst_name,
117 struct stat const *dst_stat,
118 struct stat const *src_stat,
121 /* Things to watch out for:
123 The code uses a static hash table internally and is not safe in the
124 presence of signals, multiple threads, etc. However, memory pressure
125 that prevents use of the hash table is not fatal - we just fall back
126 to redoing the computations on every call in that case.
128 int and long int might be 32 bits. Many of the calculations store
129 numbers up to 2 billion, and multiply by 10; they have to avoid
130 multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
132 time_t might be unsigned. */
134 verify (TYPE_IS_INTEGER (time_t));
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 caching information learned about 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 = NULL;
152 struct fs_res tmp_dst_res;
154 /* Time stamp resolution in nanoseconds. */
157 /* Quick exit, if possible. Since the worst resolution is 2
158 seconds, anything that differs by more than that does not
159 needs source truncation. */
160 if (dst_s == src_s && dst_ns == src_ns)
162 if (dst_s <= src_s - 2)
164 if (src_s <= dst_s - 2)
167 /* Try to do a hash lookup, but fall back to stack variables and
168 recomputation on low memory situations. */
170 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
175 new_dst_res = malloc (sizeof *new_dst_res);
178 new_dst_res->resolution = 2 * BILLION;
179 new_dst_res->exact = false;
181 new_dst_res->dev = dst_stat->st_dev;
182 dst_res = hash_insert (ht, new_dst_res);
186 if (dst_res == new_dst_res)
188 /* NEW_DST_RES is now in use in the hash table, so allocate a
189 new entry next time. */
198 tmp_dst_res.dev = dst_stat->st_dev;
199 dst_res = hash_lookup (ht, &tmp_dst_res);
203 dst_res = &tmp_dst_res;
204 dst_res->resolution = 2 * BILLION;
205 dst_res->exact = false;
209 res = dst_res->resolution;
211 #ifdef _PC_TIMESTAMP_RESOLUTION
212 /* If the system will tell us the resolution, we're set! */
213 if (! dst_res->exact)
215 res = pathconf (dst_name, _PC_TIMESTAMP_RESOLUTION);
218 dst_res->resolution = res;
219 dst_res->exact = true;
224 if (! dst_res->exact)
226 /* This file system's resolution is not known exactly.
227 Deduce it, and store the result in the hash table. */
229 time_t dst_a_s = dst_stat->st_atime;
230 time_t dst_c_s = dst_stat->st_ctime;
231 time_t dst_m_s = dst_s;
232 int dst_a_ns = get_stat_atime_ns (dst_stat);
233 int dst_c_ns = get_stat_ctime_ns (dst_stat);
234 int dst_m_ns = dst_ns;
236 /* Set RES to an upper bound on the file system resolution
237 (after truncation due to SYSCALL_RESOLUTION) by inspecting
238 the atime, ctime and mtime of the existing destination.
239 We don't know of any file system that stores atime or
240 ctime with a higher precision than mtime, so it's valid to
243 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
245 if (SYSCALL_RESOLUTION == BILLION)
247 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
256 /* Write it this way to avoid mistaken GCC warning
257 about integer overflow in constant expression. */
258 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
260 if ((a % SR10 | c % SR10 | m % SR10) != 0)
261 res = SYSCALL_RESOLUTION;
263 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
264 (res < dst_res->resolution
265 && (a % 10 | c % 10 | m % 10) == 0);
266 res *= 10, a /= 10, c /= 10, m /= 10)
275 dst_res->resolution = res;
278 if (SYSCALL_RESOLUTION < res)
280 struct timespec timespec[2];
281 struct stat dst_status;
283 /* Ignore source time stamp information that must necessarily
284 be lost when filtered through utimens. */
285 src_ns -= src_ns % SYSCALL_RESOLUTION;
287 /* If the time stamps disagree widely enough, there's no need
288 to interrogate the file system to deduce the exact time
289 stamp resolution; return the answer directly. */
291 time_t s = src_s & ~ (res == 2 * BILLION ? 1 : 0);
292 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
295 || (dst_s == s && dst_ns < src_ns - src_ns % res))
299 /* Determine the actual time stamp resolution for the
300 destination file system (after truncation due to
301 SYSCALL_RESOLUTION) by setting the access time stamp of the
302 destination to the existing access time, except with
303 trailing nonzero digits. */
305 timespec[0].tv_sec = dst_a_s;
306 timespec[0].tv_nsec = dst_a_ns;
307 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
308 timespec[1].tv_nsec = dst_m_ns + res / 9;
310 /* Set the modification time. But don't try to set the
311 modification time of symbolic links; on many hosts this sets
312 the time of the pointed-to file. */
313 if ((S_ISLNK (dst_stat->st_mode)
314 ? lutimens (dst_name, timespec)
315 : utimens (dst_name, timespec)) != 0)
318 /* Read the modification time that was set. */
320 int stat_result = (S_ISLNK (dst_stat->st_mode)
321 ? lstat (dst_name, &dst_status)
322 : stat (dst_name, &dst_status));
325 | (dst_status.st_mtime ^ dst_m_s)
326 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
328 /* The modification time changed, or we can't tell whether
329 it changed. Change it back as best we can. */
330 timespec[1].tv_sec = dst_m_s;
331 timespec[1].tv_nsec = dst_m_ns;
332 if (S_ISLNK (dst_stat->st_mode))
333 lutimens (dst_name, timespec);
335 utimens (dst_name, timespec);
338 if (stat_result != 0)
342 /* Determine the exact resolution from the modification time
343 that was read back. */
346 int a = (BILLION * (dst_status.st_mtime & 1)
347 + get_stat_mtime_ns (&dst_status));
349 res = SYSCALL_RESOLUTION;
351 for (a /= res; a % 10 == 0; a /= 10)
365 dst_res->resolution = res;
366 dst_res->exact = true;
369 /* Truncate the source's time stamp according to the resolution. */
370 src_s &= ~ (res == 2 * BILLION ? 1 : 0);
371 src_ns -= src_ns % res;
374 /* Compare the time stamps and return -1, 0, 1 accordingly. */
375 return (dst_s < src_s ? -1
377 : dst_ns < src_ns ? -1