1 /* utimecmp.c -- compare file time stamps
3 Copyright (C) 2004, 2005, 2006 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. */
33 #include "stat-time.h"
40 # define MAX(a, b) ((a) > (b) ? (a) : (b))
44 # define SIZE_MAX ((size_t) -1)
47 enum { BILLION = 1000 * 1000 * 1000 };
49 /* Best possible resolution that utimens can set and stat can return,
50 due to system-call limitations. It must be a power of 10 that is
51 no greater than 1 billion. */
52 #if (HAVE_WORKING_UTIMES \
53 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
54 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
55 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
56 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
57 || defined HAVE_STRUCT_STAT_ST_SPARE1))
58 enum { SYSCALL_RESOLUTION = 1000 };
60 enum { SYSCALL_RESOLUTION = BILLION };
63 /* Describe a file system and its time stamp resolution in nanoseconds. */
66 /* Device number of file system. */
69 /* An upper bound on the time stamp resolution of this file system,
70 ignoring any resolution that cannot be set via utimens. It is
71 represented by an integer count of nanoseconds. It must be
72 either 2 billion, or a power of 10 that is no greater than a
73 billion and is no less than SYSCALL_RESOLUTION. */
76 /* True if RESOLUTION is known to be exact, and is not merely an
77 upper bound on the true resolution. */
81 /* Hash some device info. */
83 dev_info_hash (void const *x, size_t table_size)
85 struct fs_res const *p = x;
87 /* Beware signed arithmetic gotchas. */
88 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
90 uintmax_t dev = p->dev;
91 return dev % table_size;
94 return p->dev % table_size;
97 /* Compare two dev_info structs. */
99 dev_info_compare (void const *x, void const *y)
101 struct fs_res const *a = x;
102 struct fs_res const *b = y;
103 return a->dev == b->dev;
106 /* Return -1, 0, 1 based on whether the destination file (with name
107 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
108 as SRC_STAT, or newer than SRC_STAT, respectively.
110 If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
111 converted to the destination's timestamp resolution as filtered through
112 utimens. In this case, return -2 if the exact answer cannot be
113 determined; this can happen only if the time stamps are very close and
114 there is some trouble accessing the file system (e.g., the user does not
115 have permission to futz with the destination's time stamps). */
118 utimecmp (char const *dst_name,
119 struct stat const *dst_stat,
120 struct stat const *src_stat,
123 /* Things to watch out for:
125 The code uses a static hash table internally and is not safe in the
126 presence of signals, multiple threads, etc.
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));
135 verify (TYPE_TWOS_COMPLEMENT (int));
137 /* Destination and source time stamps. */
138 time_t dst_s = dst_stat->st_mtime;
139 time_t src_s = src_stat->st_mtime;
140 int dst_ns = get_stat_mtime_ns (dst_stat);
141 int src_ns = get_stat_mtime_ns (src_stat);
143 if (options & UTIMECMP_TRUNCATE_SOURCE)
145 /* Look up the time stamp resolution for the destination device. */
147 /* Hash table for devices. */
148 static Hash_table *ht;
150 /* Information about the destination file system. */
151 static struct fs_res *new_dst_res;
152 struct fs_res *dst_res;
154 /* Time stamp resolution in nanoseconds. */
158 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
161 new_dst_res = xmalloc (sizeof *new_dst_res);
162 new_dst_res->resolution = 2 * BILLION;
163 new_dst_res->exact = false;
165 new_dst_res->dev = dst_stat->st_dev;
166 dst_res = hash_insert (ht, new_dst_res);
170 if (dst_res == new_dst_res)
172 /* NEW_DST_RES is now in use in the hash table, so allocate a
173 new entry next time. */
177 res = dst_res->resolution;
179 if (! dst_res->exact)
181 /* This file system's resolution is not known exactly.
182 Deduce it, and store the result in the hash table. */
184 time_t dst_a_s = dst_stat->st_atime;
185 time_t dst_c_s = dst_stat->st_ctime;
186 time_t dst_m_s = dst_s;
187 int dst_a_ns = get_stat_atime_ns (dst_stat);
188 int dst_c_ns = get_stat_ctime_ns (dst_stat);
189 int dst_m_ns = dst_ns;
191 /* Set RES to an upper bound on the file system resolution
192 (after truncation due to SYSCALL_RESOLUTION) by inspecting
193 the atime, ctime and mtime of the existing destination.
194 We don't know of any file system that stores atime or
195 ctime with a higher precision than mtime, so it's valid to
198 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
200 if (SYSCALL_RESOLUTION == BILLION)
202 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
211 /* Write it this way to avoid mistaken GCC warning
212 about integer overflow in constant expression. */
213 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
215 if ((a % SR10 | c % SR10 | m % SR10) != 0)
216 res = SYSCALL_RESOLUTION;
218 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
219 (res < dst_res->resolution
220 && (a % 10 | c % 10 | m % 10) == 0);
221 res *= 10, a /= 10, c /= 10, m /= 10)
230 dst_res->resolution = res;
233 if (SYSCALL_RESOLUTION < res)
235 struct timespec timespec[2];
236 struct stat dst_status;
238 /* Ignore source time stamp information that must necessarily
239 be lost when filtered through utimens. */
240 src_ns -= src_ns % SYSCALL_RESOLUTION;
242 /* If the time stamps disagree widely enough, there's no need
243 to interrogate the file system to deduce the exact time
244 stamp resolution; return the answer directly. */
246 time_t s = src_s & ~ (res == 2 * BILLION);
247 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
250 || (dst_s == s && dst_ns < src_ns - src_ns % res))
254 /* Determine the actual time stamp resolution for the
255 destination file system (after truncation due to
256 SYSCALL_RESOLUTION) by setting the access time stamp of the
257 destination to the existing access time, except with
258 trailing nonzero digits. */
260 timespec[0].tv_sec = dst_a_s;
261 timespec[0].tv_nsec = dst_a_ns;
262 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
263 timespec[1].tv_nsec = dst_m_ns + res / 9;
265 /* Set the modification time. But don't try to set the
266 modification time of symbolic links; on many hosts this sets
267 the time of the pointed-to file. */
268 if (S_ISLNK (dst_stat->st_mode)
269 || utimens (dst_name, timespec) != 0)
272 /* Read the modification time that was set. It's safe to call
273 'stat' here instead of worrying about 'lstat'; either the
274 caller used 'stat', or the caller used 'lstat' and found
275 something other than a symbolic link. */
277 int stat_result = stat (dst_name, &dst_status);
280 | (dst_status.st_mtime ^ dst_m_s)
281 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
283 /* The modification time changed, or we can't tell whether
284 it changed. Change it back as best we can. */
285 timespec[1].tv_sec = dst_m_s;
286 timespec[1].tv_nsec = dst_m_ns;
287 utimens (dst_name, timespec);
290 if (stat_result != 0)
294 /* Determine the exact resolution from the modification time
295 that was read back. */
298 int a = (BILLION * (dst_status.st_mtime & 1)
299 + get_stat_mtime_ns (&dst_status));
301 res = SYSCALL_RESOLUTION;
303 for (a /= res; a % 10 != 0; a /= 10)
317 dst_res->resolution = res;
318 dst_res->exact = true;
321 /* Truncate the source's time stamp according to the resolution. */
322 src_s &= ~ (res == 2 * BILLION);
323 src_ns -= src_ns % res;
326 /* Compare the time stamps and return -1, 0, 1 accordingly. */
327 return (dst_s < src_s ? -1
329 : dst_ns < src_ns ? -1