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. */
31 #include "stat-time.h"
38 # define MAX(a, b) ((a) > (b) ? (a) : (b))
42 # define SIZE_MAX ((size_t) -1)
45 enum { BILLION = 1000 * 1000 * 1000 };
47 /* Best possible resolution that utimens can set and stat can return,
48 due to system-call limitations. It must be a power of 10 that is
49 no greater than 1 billion. */
50 #if (HAVE_WORKING_UTIMES \
51 && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
52 || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
53 || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
54 || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
55 || defined HAVE_STRUCT_STAT_ST_SPARE1))
56 enum { SYSCALL_RESOLUTION = 1000 };
58 enum { SYSCALL_RESOLUTION = BILLION };
61 /* Describe a file system and its time stamp resolution in nanoseconds. */
64 /* Device number of file system. */
67 /* An upper bound on the time stamp resolution of this file system,
68 ignoring any resolution that cannot be set via utimens. It is
69 represented by an integer count of nanoseconds. It must be
70 either 2 billion, or a power of 10 that is no greater than a
71 billion and is no less than SYSCALL_RESOLUTION. */
74 /* True if RESOLUTION is known to be exact, and is not merely an
75 upper bound on the true resolution. */
79 /* Hash some device info. */
81 dev_info_hash (void const *x, size_t table_size)
83 struct fs_res const *p = x;
85 /* Beware signed arithmetic gotchas. */
86 if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
88 uintmax_t dev = p->dev;
89 return dev % table_size;
92 return p->dev % table_size;
95 /* Compare two dev_info structs. */
97 dev_info_compare (void const *x, void const *y)
99 struct fs_res const *a = x;
100 struct fs_res const *b = y;
101 return a->dev == b->dev;
104 /* Return -1, 0, 1 based on whether the destination file (with name
105 DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
106 as SRC_STAT, or newer than SRC_STAT, respectively.
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.
126 int and long int might be 32 bits. Many of the calculations store
127 numbers up to 2 billion, and multiply by 10; they have to avoid
128 multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
130 time_t might be unsigned. */
132 verify (TYPE_IS_INTEGER (time_t));
133 verify (TYPE_TWOS_COMPLEMENT (int));
135 /* Destination and source time stamps. */
136 time_t dst_s = dst_stat->st_mtime;
137 time_t src_s = src_stat->st_mtime;
138 int dst_ns = get_stat_mtime_ns (dst_stat);
139 int src_ns = get_stat_mtime_ns (src_stat);
141 if (options & UTIMECMP_TRUNCATE_SOURCE)
143 /* Look up the time stamp resolution for the destination device. */
145 /* Hash table for devices. */
146 static Hash_table *ht;
148 /* Information about the destination file system. */
149 static struct fs_res *new_dst_res;
150 struct fs_res *dst_res;
152 /* Time stamp resolution in nanoseconds. */
156 ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
159 new_dst_res = xmalloc (sizeof *new_dst_res);
160 new_dst_res->resolution = 2 * BILLION;
161 new_dst_res->exact = false;
163 new_dst_res->dev = dst_stat->st_dev;
164 dst_res = hash_insert (ht, new_dst_res);
168 if (dst_res == new_dst_res)
170 /* NEW_DST_RES is now in use in the hash table, so allocate a
171 new entry next time. */
175 res = dst_res->resolution;
177 if (! dst_res->exact)
179 /* This file system's resolution is not known exactly.
180 Deduce it, and store the result in the hash table. */
182 time_t dst_a_s = dst_stat->st_atime;
183 time_t dst_c_s = dst_stat->st_ctime;
184 time_t dst_m_s = dst_s;
185 int dst_a_ns = get_stat_atime_ns (dst_stat);
186 int dst_c_ns = get_stat_ctime_ns (dst_stat);
187 int dst_m_ns = dst_ns;
189 /* Set RES to an upper bound on the file system resolution
190 (after truncation due to SYSCALL_RESOLUTION) by inspecting
191 the atime, ctime and mtime of the existing destination.
192 We don't know of any file system that stores atime or
193 ctime with a higher precision than mtime, so it's valid to
196 bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
198 if (SYSCALL_RESOLUTION == BILLION)
200 if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
209 /* Write it this way to avoid mistaken GCC warning
210 about integer overflow in constant expression. */
211 int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
213 if ((a % SR10 | c % SR10 | m % SR10) != 0)
214 res = SYSCALL_RESOLUTION;
216 for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
217 (res < dst_res->resolution
218 && (a % 10 | c % 10 | m % 10) == 0);
219 res *= 10, a /= 10, c /= 10, m /= 10)
228 dst_res->resolution = res;
231 if (SYSCALL_RESOLUTION < res)
233 struct timespec timespec[2];
234 struct stat dst_status;
236 /* Ignore source time stamp information that must necessarily
237 be lost when filtered through utimens. */
238 src_ns -= src_ns % SYSCALL_RESOLUTION;
240 /* If the time stamps disagree widely enough, there's no need
241 to interrogate the file system to deduce the exact time
242 stamp resolution; return the answer directly. */
244 time_t s = src_s & ~ (res == 2 * BILLION);
245 if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
248 || (dst_s == s && dst_ns < src_ns - src_ns % res))
252 /* Determine the actual time stamp resolution for the
253 destination file system (after truncation due to
254 SYSCALL_RESOLUTION) by setting the access time stamp of the
255 destination to the existing access time, except with
256 trailing nonzero digits. */
258 timespec[0].tv_sec = dst_a_s;
259 timespec[0].tv_nsec = dst_a_ns;
260 timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
261 timespec[1].tv_nsec = dst_m_ns + res / 9;
263 /* Set the modification time. But don't try to set the
264 modification time of symbolic links; on many hosts this sets
265 the time of the pointed-to file. */
266 if (S_ISLNK (dst_stat->st_mode)
267 || utimens (dst_name, timespec) != 0)
270 /* Read the modification time that was set. It's safe to call
271 'stat' here instead of worrying about 'lstat'; either the
272 caller used 'stat', or the caller used 'lstat' and found
273 something other than a symbolic link. */
275 int stat_result = stat (dst_name, &dst_status);
278 | (dst_status.st_mtime ^ dst_m_s)
279 | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
281 /* The modification time changed, or we can't tell whether
282 it changed. Change it back as best we can. */
283 timespec[1].tv_sec = dst_m_s;
284 timespec[1].tv_nsec = dst_m_ns;
285 utimens (dst_name, timespec);
288 if (stat_result != 0)
292 /* Determine the exact resolution from the modification time
293 that was read back. */
296 int a = (BILLION * (dst_status.st_mtime & 1)
297 + get_stat_mtime_ns (&dst_status));
299 res = SYSCALL_RESOLUTION;
301 for (a /= res; a % 10 != 0; a /= 10)
315 dst_res->resolution = res;
316 dst_res->exact = true;
319 /* Truncate the source's time stamp according to the resolution. */
320 src_s &= ~ (res == 2 * BILLION);
321 src_ns -= src_ns % res;
324 /* Compare the time stamps and return -1, 0, 1 accordingly. */
325 return (dst_s < src_s ? -1
327 : dst_ns < src_ns ? -1