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+/* utimecmp.c -- compare file timestamps
+
+ Copyright (C) 2004-2007, 2009-2022 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* Written by Paul Eggert. */
+
+#include <config.h>
+
+#include "utimecmp.h"
+
+#include <fcntl.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "dirname.h"
+#include "hash.h"
+#include "intprops.h"
+#include "stat-time.h"
+#include "verify.h"
+
+#ifndef MAX
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
+#define BILLION (1000 * 1000 * 1000)
+
+/* Best possible resolution that utimens can set and stat can return,
+ due to system-call limitations. It must be a power of 10 that is
+ no greater than 1 billion. */
+#if HAVE_UTIMENSAT
+enum { SYSCALL_RESOLUTION = 1 };
+#elif defined _WIN32 && ! defined __CYGWIN__
+/* On native Windows, file times have 100 ns resolution. See
+ <https://docs.microsoft.com/en-us/windows/desktop/api/minwinbase/ns-minwinbase-filetime> */
+enum { SYSCALL_RESOLUTION = 100 };
+#elif ((HAVE_FUTIMESAT || HAVE_WORKING_UTIMES) \
+ && (defined HAVE_STRUCT_STAT_ST_ATIM_TV_NSEC \
+ || defined HAVE_STRUCT_STAT_ST_ATIMESPEC_TV_NSEC \
+ || defined HAVE_STRUCT_STAT_ST_ATIMENSEC \
+ || defined HAVE_STRUCT_STAT_ST_ATIM_ST__TIM_TV_NSEC \
+ || defined HAVE_STRUCT_STAT_ST_SPARE1))
+enum { SYSCALL_RESOLUTION = 1000 };
+#else
+enum { SYSCALL_RESOLUTION = BILLION };
+#endif
+
+/* Describe a file system and its timestamp resolution in nanoseconds. */
+struct fs_res
+{
+ /* Device number of file system. */
+ dev_t dev;
+
+ /* An upper bound on the timestamp resolution of this file system,
+ ignoring any resolution that cannot be set via utimens. It is
+ represented by an integer count of nanoseconds. It must be
+ either 2 billion, or a power of 10 that is no greater than a
+ billion and is no less than SYSCALL_RESOLUTION. */
+ int resolution;
+
+ /* True if RESOLUTION is known to be exact, and is not merely an
+ upper bound on the true resolution. */
+ bool exact;
+};
+
+/* Hash some device info. */
+static size_t
+dev_info_hash (void const *x, size_t table_size)
+{
+ struct fs_res const *p = x;
+
+ /* Beware signed arithmetic gotchas. */
+ if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
+ {
+ uintmax_t dev = p->dev;
+ return dev % table_size;
+ }
+
+ return p->dev % table_size;
+}
+
+/* Compare two dev_info structs. */
+static bool
+dev_info_compare (void const *x, void const *y)
+{
+ struct fs_res const *a = x;
+ struct fs_res const *b = y;
+ return a->dev == b->dev;
+}
+
+/* Return -1, 0, 1 based on whether the destination file (relative
+ to openat-like directory file descriptor DFD with name
+ DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
+ as SRC_STAT, or newer than SRC_STAT, respectively.
+
+ DST_NAME may be NULL if OPTIONS is 0.
+
+ If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
+ converted to the destination's timestamp resolution as filtered through
+ utimens. In this case, return -2 if the exact answer cannot be
+ determined; this can happen only if the timestamps are very close and
+ there is some trouble accessing the file system (e.g., the user does not
+ have permission to futz with the destination's timestamps). */
+
+int
+utimecmp (char const *dst_name,
+ struct stat const *dst_stat,
+ struct stat const *src_stat,
+ int options)
+{
+ return utimecmpat (AT_FDCWD, dst_name, dst_stat, src_stat, options);
+}
+
+int
+utimecmpat (int dfd, char const *dst_name,
+ struct stat const *dst_stat,
+ struct stat const *src_stat,
+ int options)
+{
+ /* Things to watch out for:
+
+ The code uses a static hash table internally and is not safe in the
+ presence of signals, multiple threads, etc. However, memory pressure
+ that prevents use of the hash table is not fatal - we just fall back
+ to redoing the computations on every call in that case.
+
+ int and long int might be 32 bits. Many of the calculations store
+ numbers up to 2 billion, and multiply by 10; they have to avoid
+ multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
+
+ time_t might be unsigned. */
+
+ verify (TYPE_IS_INTEGER (time_t));
+
+ /* Destination and source timestamps. */
+ time_t dst_s = dst_stat->st_mtime;
+ time_t src_s = src_stat->st_mtime;
+ int dst_ns = get_stat_mtime_ns (dst_stat);
+ int src_ns = get_stat_mtime_ns (src_stat);
+
+ if (options & UTIMECMP_TRUNCATE_SOURCE)
+ {
+#if defined _AIX
+ /* On AIX 7.2, on a jfs2 file system, the times may differ by up to
+ 0.01 seconds in either direction. But it does not seem to come
+ from clock ticks of 0.01 seconds each. */
+ long long difference =
+ ((long long) dst_s - (long long) src_s) * BILLION
+ + ((long long) dst_ns - (long long) src_ns);
+ if (difference < 10000000 && difference > -10000000)
+ return 0;
+#endif
+
+ /* Look up the timestamp resolution for the destination device. */
+
+ /* Hash table for caching information learned about devices. */
+ static Hash_table *ht;
+
+ /* Information about the destination file system. */
+ static struct fs_res *new_dst_res;
+ struct fs_res *dst_res = NULL;
+ struct fs_res tmp_dst_res;
+
+ /* timestamp resolution in nanoseconds. */
+ int res;
+
+ /* Quick exit, if possible. Since the worst resolution is 2
+ seconds, anything that differs by more than that does not
+ needs source truncation. */
+ if (dst_s == src_s && dst_ns == src_ns)
+ return 0;
+ if (dst_s <= src_s - 2)
+ return -1;
+ if (src_s <= dst_s - 2)
+ return 1;
+
+ /* Try to do a hash lookup, but fall back to stack variables and
+ recomputation on low memory situations. */
+ if (! ht)
+ ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
+ if (ht)
+ {
+ if (! new_dst_res)
+ {
+ new_dst_res = malloc (sizeof *new_dst_res);
+ if (!new_dst_res)
+ goto low_memory;
+ new_dst_res->resolution = 2 * BILLION;
+ new_dst_res->exact = false;
+ }
+ new_dst_res->dev = dst_stat->st_dev;
+ dst_res = hash_insert (ht, new_dst_res);
+ if (! dst_res)
+ goto low_memory;
+
+ if (dst_res == new_dst_res)
+ {
+ /* NEW_DST_RES is now in use in the hash table, so allocate a
+ new entry next time. */
+ new_dst_res = NULL;
+ }
+ }
+ else
+ {
+ low_memory:
+ if (ht)
+ {
+ tmp_dst_res.dev = dst_stat->st_dev;
+ dst_res = hash_lookup (ht, &tmp_dst_res);
+ }
+ if (!dst_res)
+ {
+ dst_res = &tmp_dst_res;
+ dst_res->resolution = 2 * BILLION;
+ dst_res->exact = false;
+ }
+ }
+
+ res = dst_res->resolution;
+
+#ifdef _PC_TIMESTAMP_RESOLUTION
+ /* If the system will tell us the resolution, we're set! */
+ if (! dst_res->exact)
+ {
+ res = -1;
+ if (dfd == AT_FDCWD)
+ res = pathconf (dst_name, _PC_TIMESTAMP_RESOLUTION);
+ else
+ {
+ char *dstdir = mdir_name (dst_name);
+ if (dstdir)
+ {
+ int destdirfd = openat (dfd, dstdir,
+ O_SEARCH | O_CLOEXEC | O_DIRECTORY);
+ if (0 <= destdirfd)
+ {
+ res = fpathconf (destdirfd, _PC_TIMESTAMP_RESOLUTION);
+ close (destdirfd);
+ }
+ free (dstdir);
+ }
+ }
+ if (0 < res)
+ {
+ dst_res->resolution = res;
+ dst_res->exact = true;
+ }
+ }
+#endif
+
+ if (! dst_res->exact)
+ {
+ /* This file system's resolution is not known exactly.
+ Deduce it, and store the result in the hash table. */
+
+ time_t dst_a_s = dst_stat->st_atime;
+ time_t dst_c_s = dst_stat->st_ctime;
+ time_t dst_m_s = dst_s;
+ int dst_a_ns = get_stat_atime_ns (dst_stat);
+ int dst_c_ns = get_stat_ctime_ns (dst_stat);
+ int dst_m_ns = dst_ns;
+
+ /* Set RES to an upper bound on the file system resolution
+ (after truncation due to SYSCALL_RESOLUTION) by inspecting
+ the atime, ctime and mtime of the existing destination.
+ We don't know of any file system that stores atime or
+ ctime with a higher precision than mtime, so it's valid to
+ look at them too. */
+ {
+ bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
+
+ if (SYSCALL_RESOLUTION == BILLION)
+ {
+ if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
+ res = BILLION;
+ }
+ else
+ {
+ int a = dst_a_ns;
+ int c = dst_c_ns;
+ int m = dst_m_ns;
+
+ /* Write it this way to avoid mistaken GCC warning
+ about integer overflow in constant expression. */
+ int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
+
+ if ((a % SR10 | c % SR10 | m % SR10) != 0)
+ res = SYSCALL_RESOLUTION;
+ else
+ for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
+ (res < dst_res->resolution
+ && (a % 10 | c % 10 | m % 10) == 0);
+ res *= 10, a /= 10, c /= 10, m /= 10)
+ if (res == BILLION)
+ {
+ if (! odd_second)
+ res *= 2;
+ break;
+ }
+ }
+
+ dst_res->resolution = res;
+ }
+
+ if (SYSCALL_RESOLUTION < res)
+ {
+ struct timespec timespec[2];
+ struct stat dst_status;
+
+ /* Ignore source timestamp information that must necessarily
+ be lost when filtered through utimens. */
+ src_ns -= src_ns % SYSCALL_RESOLUTION;
+
+ /* If the timestamps disagree widely enough, there's no need
+ to interrogate the file system to deduce the exact
+ timestamp resolution; return the answer directly. */
+ {
+ time_t s = src_s & ~ (res == 2 * BILLION ? 1 : 0);
+ if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
+ return 1;
+ if (dst_s < s
+ || (dst_s == s && dst_ns < src_ns - src_ns % res))
+ return -1;
+ }
+
+ /* Determine the actual timestamp resolution for the
+ destination file system (after truncation due to
+ SYSCALL_RESOLUTION) by setting the access timestamp of the
+ destination to the existing access time, except with
+ trailing nonzero digits. */
+
+ timespec[0].tv_sec = dst_a_s;
+ timespec[0].tv_nsec = dst_a_ns;
+ timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
+ timespec[1].tv_nsec = dst_m_ns + res / 9;
+
+ if (utimensat (dfd, dst_name, timespec, AT_SYMLINK_NOFOLLOW))
+ return -2;
+
+ /* Read the modification time that was set. */
+ {
+ int stat_result
+ = fstatat (dfd, dst_name, &dst_status, AT_SYMLINK_NOFOLLOW);
+
+ if (stat_result
+ | (dst_status.st_mtime ^ dst_m_s)
+ | (get_stat_mtime_ns (&dst_status) ^ dst_m_ns))
+ {
+ /* The modification time changed, or we can't tell whether
+ it changed. Change it back as best we can. */
+ timespec[1].tv_sec = dst_m_s;
+ timespec[1].tv_nsec = dst_m_ns;
+ utimensat (dfd, dst_name, timespec, AT_SYMLINK_NOFOLLOW);
+ }
+
+ if (stat_result != 0)
+ return -2;
+ }
+
+ /* Determine the exact resolution from the modification time
+ that was read back. */
+ {
+ int old_res = res;
+ int a = (BILLION * (dst_status.st_mtime & 1)
+ + get_stat_mtime_ns (&dst_status));
+
+ res = SYSCALL_RESOLUTION;
+
+ for (a /= res; a % 10 == 0; a /= 10)
+ {
+ if (res == BILLION)
+ {
+ res *= 2;
+ break;
+ }
+ res *= 10;
+ if (res == old_res)
+ break;
+ }
+ }
+ }
+
+ dst_res->resolution = res;
+ dst_res->exact = true;
+ }
+
+ /* Truncate the source's timestamp according to the resolution. */
+ src_s &= ~ (res == 2 * BILLION ? 1 : 0);
+ src_ns -= src_ns % res;
+ }
+
+ /* Compare the timestamps and return -1, 0, 1 accordingly. */
+ return (_GL_CMP (dst_s, src_s)
+ + ((dst_s == src_s ? ~0 : 0) & _GL_CMP (dst_ns, src_ns)));
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-03 00:36:58 +0000