1 /* utimecmp.c -- compare file time stamps
3 Copyright (C) 2004, 2005 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 2, or (at your option)
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, write to the Free Software Foundation,
17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
19 /* Written by Paul Eggert. */
28 # include <inttypes.h>
39 #include "stat-time.h"
46 # define MAX(a, b) ((a) > (b) ? (a) : (b))
50 # define SIZE_MAX ((size_t) -1)
53 enum { BILLION = 1000 * 1000 * 1000 };
55 /* Best possible resolution that utimens can set and stat can return,
56 due to system-call limitations. It must be a power of 10 that is
57 no greater than 1 billion. */
58 #if (HAVE_WORKING_UTIMES \
59 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
60 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
61 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
62 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
63 || defined HAVE_STRUCT_STAT_ST_SPARE1))
64 enum { SYSCALL_RESOLUTION = 1000 };
66 enum { SYSCALL_RESOLUTION = BILLION };
69 /* Describe a file system and its time stamp resolution in nanoseconds. */
72 /* Device number of file system. */
75 /* An upper bound on the time stamp resolution of this file system,
76 ignoring any resolution that cannot be set via utimens. It is
77 represented by an integer count of nanoseconds. It must be
78 either 2 billion, or a power of 10 that is no greater than a
79 billion and is no less than SYSCALL_RESOLUTION. */
82 /* True if RESOLUTION is known to be exact, and is not merely an
83 upper bound on the true resolution. */
87 /* Hash some device info. */
89 dev_info_hash (void const *x, size_t table_size)
91 struct fs_res const *p = x;
93 /* Beware signed arithmetic gotchas. */
94 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
96 uintmax_t dev = p->dev;
97 return dev % table_size;
100 return p->dev % table_size;
103 /* Compare two dev_info structs. */
105 dev_info_compare (void const *x, void const *y)
107 struct fs_res const *a = x;
108 struct fs_res const *b = y;
109 return a->dev == b->dev;
112 /* Return -1, 0, 1 based on whether the destination file (with name
113 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
114 as SRC_STAT, or newer than SRC_STAT, respectively.
116 If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
117 converted to the destination's timestamp resolution as filtered through
118 utimens. In this case, return -2 if the exact answer cannot be
119 determined; this can happen only if the time stamps are very close and
120 there is some trouble accessing the file system (e.g., the user does not
121 have permission to futz with the destination's time stamps). */
124 utimecmp (char const *dst_name,
125 struct stat const *dst_stat,
126 struct stat const *src_stat,
129 /* Things to watch out for:
131 The code uses a static hash table internally and is not safe in the
132 presence of signals, multiple threads, etc.
134 int and long int might be 32 bits. Many of the calculations store
135 numbers up to 2 billion, and multiply by 10; they have to avoid
136 multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
138 time_t might be unsigned. */
140 verify (TYPE_IS_INTEGER (time_t));
141 verify (TYPE_TWOS_COMPLEMENT (int));
143 /* Destination and source time stamps. */
144 time_t dst_s = dst_stat->st_mtime;
145 time_t src_s = src_stat->st_mtime;
146 int dst_ns = get_stat_mtime_ns (dst_stat);
147 int src_ns = get_stat_mtime_ns (src_stat);
149 if (options & UTIMECMP_TRUNCATE_SOURCE)
151 /* Look up the time stamp resolution for the destination device. */
153 /* Hash table for devices. */
154 static Hash_table *ht;
156 /* Information about the destination file system. */
157 static struct fs_res *new_dst_res;
158 struct fs_res *dst_res;
160 /* Time stamp resolution in nanoseconds. */
164 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
167 new_dst_res = xmalloc (sizeof *new_dst_res);
168 new_dst_res->resolution = 2 * BILLION;
169 new_dst_res->exact = false;
171 new_dst_res->dev = dst_stat->st_dev;
172 dst_res = hash_insert (ht, new_dst_res);
176 if (dst_res == new_dst_res)
178 /* NEW_DST_RES is now in use in the hash table, so allocate a
179 new entry next time. */
183 res = dst_res->resolution;
185 if (! dst_res->exact)
187 /* This file system's resolution is not known exactly.
188 Deduce it, and store the result in the hash table. */
190 time_t dst_a_s = dst_stat->st_atime;
191 time_t dst_c_s = dst_stat->st_ctime;
192 time_t dst_m_s = dst_s;
193 int dst_a_ns = get_stat_atime_ns (dst_stat);
194 int dst_c_ns = get_stat_ctime_ns (dst_stat);
195 int dst_m_ns = dst_ns;
197 /* Set RES to an upper bound on the file system resolution
198 (after truncation due to SYSCALL_RESOLUTION) by inspecting
199 the atime, ctime and mtime of the existing destination.
200 We don't know of any file system that stores atime or
201 ctime with a higher precision than mtime, so it's valid to
204 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
206 if (SYSCALL_RESOLUTION == BILLION)
208 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
217 /* Write it this way to avoid mistaken GCC warning
218 about integer overflow in constant expression. */
219 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
221 if ((a % SR10 | c % SR10 | m % SR10) != 0)
222 res = SYSCALL_RESOLUTION;
224 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
225 (res < dst_res->resolution
226 && (a % 10 | c % 10 | m % 10) == 0);
227 res *= 10, a /= 10, c /= 10, m /= 10)
236 dst_res->resolution = res;
239 if (SYSCALL_RESOLUTION < res)
241 struct timespec timespec[2];
242 struct stat dst_status;
244 /* Ignore source time stamp information that must necessarily
245 be lost when filtered through utimens. */
246 src_ns -= src_ns % SYSCALL_RESOLUTION;
248 /* If the time stamps disagree widely enough, there's no need
249 to interrogate the file system to deduce the exact time
250 stamp resolution; return the answer directly. */
252 time_t s = src_s & ~ (res == 2 * BILLION);
253 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
256 || (dst_s == s && dst_ns < src_ns - src_ns % res))
260 /* Determine the actual time stamp resolution for the
261 destination file system (after truncation due to
262 SYSCALL_RESOLUTION) by setting the access time stamp of the
263 destination to the existing access time, except with
264 trailing nonzero digits. */
266 timespec[0].tv_sec = dst_a_s;
267 timespec[0].tv_nsec = dst_a_ns;
268 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
269 timespec[1].tv_nsec = dst_m_ns + res / 9;
271 /* Set the modification time. But don't try to set the
272 modification time of symbolic links; on many hosts this sets
273 the time of the pointed-to file. */
274 if (S_ISLNK (dst_stat->st_mode)
275 || utimens (dst_name, timespec) != 0)
278 /* Read the modification time that was set. It's safe to call
279 'stat' here instead of worrying about 'lstat'; either the
280 caller used 'stat', or the caller used 'lstat' and found
281 something other than a symbolic link. */
283 int stat_result = stat (dst_name, &dst_status);
286 | (dst_status.st_mtime ^ dst_m_s)
287 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
289 /* The modification time changed, or we can't tell whether
290 it changed. Change it back as best we can. */
291 timespec[1].tv_sec = dst_m_s;
292 timespec[1].tv_nsec = dst_m_ns;
293 utimens (dst_name, timespec);
296 if (stat_result != 0)
300 /* Determine the exact resolution from the modification time
301 that was read back. */
304 int a = (BILLION * (dst_status.st_mtime & 1)
305 + get_stat_mtime_ns (&dst_status));
307 res = SYSCALL_RESOLUTION;
309 for (a /= res; a % 10 != 0; a /= 10)
323 dst_res->resolution = res;
324 dst_res->exact = true;
327 /* Truncate the source's time stamp according to the resolution. */
328 src_s &= ~ (res == 2 * BILLION);
329 src_ns -= src_ns % res;
332 /* Compare the time stamps and return -1, 0, 1 accordingly. */
333 return (dst_s < src_s ? -1
335 : dst_ns < src_ns ? -1