1 /* utimecmp.c -- compare file time stamps
3 Copyright (C) 2004, 2005, 2006, 2007 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. */
32 #include "stat-time.h"
38 # define MAX(a, b) ((a) > (b) ? (a) : (b))
41 enum { 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. */
46 #if (HAVE_WORKING_UTIMES \
47 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
48 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
49 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
50 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
51 || defined HAVE_STRUCT_STAT_ST_SPARE1))
52 enum { SYSCALL_RESOLUTION = 1000 };
54 enum { SYSCALL_RESOLUTION = BILLION };
57 /* Describe a file system and its time stamp resolution in nanoseconds. */
60 /* Device number of file system. */
63 /* An upper bound on the time stamp resolution of this file system,
64 ignoring any resolution that cannot be set via utimens. It is
65 represented by an integer count of nanoseconds. It must be
66 either 2 billion, or a power of 10 that is no greater than a
67 billion and is no less than SYSCALL_RESOLUTION. */
70 /* True if RESOLUTION is known to be exact, and is not merely an
71 upper bound on the true resolution. */
75 /* Hash some device info. */
77 dev_info_hash (void const *x, size_t table_size)
79 struct fs_res const *p = x;
81 /* Beware signed arithmetic gotchas. */
82 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
84 uintmax_t dev = p->dev;
85 return dev % table_size;
88 return p->dev % table_size;
91 /* Compare two dev_info structs. */
93 dev_info_compare (void const *x, void const *y)
95 struct fs_res const *a = x;
96 struct fs_res const *b = y;
97 return a->dev == b->dev;
100 /* Return -1, 0, 1 based on whether the destination file (with name
101 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
102 as SRC_STAT, or newer than SRC_STAT, respectively.
104 If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
105 converted to the destination's timestamp resolution as filtered through
106 utimens. In this case, return -2 if the exact answer cannot be
107 determined; this can happen only if the time stamps are very close and
108 there is some trouble accessing the file system (e.g., the user does not
109 have permission to futz with the destination's time stamps). */
112 utimecmp (char const *dst_name,
113 struct stat const *dst_stat,
114 struct stat const *src_stat,
117 /* Things to watch out for:
119 The code uses a static hash table internally and is not safe in the
120 presence of signals, multiple threads, etc.
122 int and long int might be 32 bits. Many of the calculations store
123 numbers up to 2 billion, and multiply by 10; they have to avoid
124 multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
126 time_t might be unsigned. */
128 verify (TYPE_IS_INTEGER (time_t));
129 verify (TYPE_TWOS_COMPLEMENT (int));
131 /* Destination and source time stamps. */
132 time_t dst_s = dst_stat->st_mtime;
133 time_t src_s = src_stat->st_mtime;
134 int dst_ns = get_stat_mtime_ns (dst_stat);
135 int src_ns = get_stat_mtime_ns (src_stat);
137 if (options & UTIMECMP_TRUNCATE_SOURCE)
139 /* Look up the time stamp resolution for the destination device. */
141 /* Hash table for devices. */
142 static Hash_table *ht;
144 /* Information about the destination file system. */
145 static struct fs_res *new_dst_res;
146 struct fs_res *dst_res;
148 /* Time stamp resolution in nanoseconds. */
152 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
155 new_dst_res = xmalloc (sizeof *new_dst_res);
156 new_dst_res->resolution = 2 * BILLION;
157 new_dst_res->exact = false;
159 new_dst_res->dev = dst_stat->st_dev;
160 dst_res = hash_insert (ht, new_dst_res);
164 if (dst_res == new_dst_res)
166 /* NEW_DST_RES is now in use in the hash table, so allocate a
167 new entry next time. */
171 res = dst_res->resolution;
173 if (! dst_res->exact)
175 /* This file system's resolution is not known exactly.
176 Deduce it, and store the result in the hash table. */
178 time_t dst_a_s = dst_stat->st_atime;
179 time_t dst_c_s = dst_stat->st_ctime;
180 time_t dst_m_s = dst_s;
181 int dst_a_ns = get_stat_atime_ns (dst_stat);
182 int dst_c_ns = get_stat_ctime_ns (dst_stat);
183 int dst_m_ns = dst_ns;
185 /* Set RES to an upper bound on the file system resolution
186 (after truncation due to SYSCALL_RESOLUTION) by inspecting
187 the atime, ctime and mtime of the existing destination.
188 We don't know of any file system that stores atime or
189 ctime with a higher precision than mtime, so it's valid to
192 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
194 if (SYSCALL_RESOLUTION == BILLION)
196 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
205 /* Write it this way to avoid mistaken GCC warning
206 about integer overflow in constant expression. */
207 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
209 if ((a % SR10 | c % SR10 | m % SR10) != 0)
210 res = SYSCALL_RESOLUTION;
212 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
213 (res < dst_res->resolution
214 && (a % 10 | c % 10 | m % 10) == 0);
215 res *= 10, a /= 10, c /= 10, m /= 10)
224 dst_res->resolution = res;
227 if (SYSCALL_RESOLUTION < res)
229 struct timespec timespec[2];
230 struct stat dst_status;
232 /* Ignore source time stamp information that must necessarily
233 be lost when filtered through utimens. */
234 src_ns -= src_ns % SYSCALL_RESOLUTION;
236 /* If the time stamps disagree widely enough, there's no need
237 to interrogate the file system to deduce the exact time
238 stamp resolution; return the answer directly. */
240 time_t s = src_s & ~ (res == 2 * BILLION);
241 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
244 || (dst_s == s && dst_ns < src_ns - src_ns % res))
248 /* Determine the actual time stamp resolution for the
249 destination file system (after truncation due to
250 SYSCALL_RESOLUTION) by setting the access time stamp of the
251 destination to the existing access time, except with
252 trailing nonzero digits. */
254 timespec[0].tv_sec = dst_a_s;
255 timespec[0].tv_nsec = dst_a_ns;
256 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
257 timespec[1].tv_nsec = dst_m_ns + res / 9;
259 /* Set the modification time. But don't try to set the
260 modification time of symbolic links; on many hosts this sets
261 the time of the pointed-to file. */
262 if (S_ISLNK (dst_stat->st_mode)
263 || utimens (dst_name, timespec) != 0)
266 /* Read the modification time that was set. It's safe to call
267 'stat' here instead of worrying about 'lstat'; either the
268 caller used 'stat', or the caller used 'lstat' and found
269 something other than a symbolic link. */
271 int stat_result = stat (dst_name, &dst_status);
274 | (dst_status.st_mtime ^ dst_m_s)
275 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
277 /* The modification time changed, or we can't tell whether
278 it changed. Change it back as best we can. */
279 timespec[1].tv_sec = dst_m_s;
280 timespec[1].tv_nsec = dst_m_ns;
281 utimens (dst_name, timespec);
284 if (stat_result != 0)
288 /* Determine the exact resolution from the modification time
289 that was read back. */
292 int a = (BILLION * (dst_status.st_mtime & 1)
293 + get_stat_mtime_ns (&dst_status));
295 res = SYSCALL_RESOLUTION;
297 for (a /= res; a % 10 != 0; a /= 10)
311 dst_res->resolution = res;
312 dst_res->exact = true;
315 /* Truncate the source's time stamp according to the resolution. */
316 src_s &= ~ (res == 2 * BILLION);
317 src_ns -= src_ns % res;
320 /* Compare the time stamps and return -1, 0, 1 accordingly. */
321 return (dst_s < src_s ? -1
323 : dst_ns < src_ns ? -1