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341 lines
10 KiB
C
341 lines
10 KiB
C
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/* utimecmp.c -- compare file time stamps
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Copyright (C) 2004 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software Foundation,
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Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
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/* Written by Paul Eggert. */
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#if HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include "utimecmp.h"
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#if HAVE_INTTYPES_H
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# include <inttypes.h>
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#endif
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#if HAVE_STDINT_H
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# include <stdint.h>
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#endif
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#include <limits.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include "hash.h"
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#include "timespec.h"
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#include "utimens.h"
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#include "xalloc.h"
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/* Verify a requirement at compile-time (unlike assert, which is runtime). */
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#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
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#ifndef MAX
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# define MAX(a, b) ((a) > (b) ? (a) : (b))
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#endif
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#ifndef SIZE_MAX
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# define SIZE_MAX ((size_t) -1)
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#endif
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/* The extra casts work around common compiler bugs. */
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#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
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/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
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It is necessary at least when t == time_t. */
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#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
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? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
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#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
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enum { BILLION = 1000 * 1000 * 1000 };
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/* Best possible resolution that utimens can set and stat can return,
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due to system-call limitations. It must be a power of 10 that is
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no greater than 1 billion. */
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#if HAVE_WORKING_UTIMES && defined ST_MTIM_NSEC
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enum { SYSCALL_RESOLUTION = 1000 };
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#else
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enum { SYSCALL_RESOLUTION = BILLION };
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#endif
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/* Describe a file system and its time stamp resolution in nanoseconds. */
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struct fs_res
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{
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/* Device number of file system. */
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dev_t dev;
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/* An upper bound on the time stamp resolution of this file system,
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ignoring any resolution that cannot be set via utimens. It is
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represented by an integer count of nanoseconds. It must be
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either 2 billion, or a power of 10 that is no greater than a
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billion and is no less than SYSCALL_RESOLUTION. */
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int resolution;
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/* True if RESOLUTION is known to be exact, and is not merely an
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upper bound on the true resolution. */
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bool exact;
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};
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/* Hash some device info. */
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static size_t
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dev_info_hash (void const *x, size_t table_size)
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{
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struct fs_res const *p = x;
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/* Beware signed arithmetic gotchas. */
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if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
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{
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uintmax_t dev = p->dev;
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return dev % table_size;
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}
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return p->dev % table_size;
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}
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/* Compare two dev_info structs. */
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static bool
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dev_info_compare (void const *x, void const *y)
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{
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struct fs_res const *a = x;
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struct fs_res const *b = y;
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return a->dev == b->dev;
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}
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/* Return -1, 0, 1 based on whether the destination file (with name
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DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
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as SRC_STAT, or newer than SRC_STAT, respectively.
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If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
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converted to the destination's timestamp resolution as filtered through
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utimens. In this case, return -2 if the exact answer cannot be
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determined; this can happen only if the time stamps are very close and
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there is some trouble accessing the file system (e.g., the user does not
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have permission to futz with the destination's time stamps). */
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int
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utimecmp (char const *dst_name,
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struct stat const *dst_stat,
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struct stat const *src_stat,
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int options)
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{
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/* Things to watch out for:
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The code uses a static hash table internally and is not safe in the
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presence of signals, multiple threads, etc.
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int and long int might be 32 bits. Many of the calculations store
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numbers up to 2 billion, and multiply by 10; they have to avoid
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multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
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time_t might be unsigned. */
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verify (time_t_is_integer, (time_t) 0.5 == 0);
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verify (twos_complement_arithmetic, -1 == ~1 + 1);
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/* Destination and source time stamps. */
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time_t dst_s = dst_stat->st_mtime;
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time_t src_s = src_stat->st_mtime;
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int dst_ns = TIMESPEC_NS (dst_stat->st_mtim);
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int src_ns = TIMESPEC_NS (src_stat->st_mtim);
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if (options & UTIMECMP_TRUNCATE_SOURCE)
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{
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/* Look up the time stamp resolution for the destination device. */
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/* Hash table for devices. */
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static Hash_table *ht;
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/* Information about the destination file system. */
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static struct fs_res *new_dst_res;
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struct fs_res *dst_res;
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/* Time stamp resolution in nanoseconds. */
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int res;
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if (! ht)
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ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
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if (! new_dst_res)
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{
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new_dst_res = xmalloc (sizeof *new_dst_res);
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new_dst_res->resolution = 2 * BILLION;
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new_dst_res->exact = false;
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}
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new_dst_res->dev = dst_stat->st_dev;
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dst_res = hash_insert (ht, new_dst_res);
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if (! dst_res)
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xalloc_die ();
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if (dst_res == new_dst_res)
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{
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/* NEW_DST_RES is now in use in the hash table, so allocate a
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new entry next time. */
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new_dst_res = NULL;
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}
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res = dst_res->resolution;
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if (! dst_res->exact)
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{
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/* This file system's resolution is not known exactly.
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Deduce it, and store the result in the hash table. */
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time_t dst_a_s = dst_stat->st_atime;
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time_t dst_c_s = dst_stat->st_ctime;
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time_t dst_m_s = dst_s;
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int dst_a_ns = TIMESPEC_NS (dst_stat->st_atim);
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int dst_c_ns = TIMESPEC_NS (dst_stat->st_ctim);
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int dst_m_ns = dst_ns;
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/* Set RES to an upper bound on the file system resolution
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(after truncation due to SYSCALL_RESOLUTION) by inspecting
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the atime, ctime and mtime of the existing destination.
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We don't know of any file system that stores atime or
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ctime with a higher precision than mtime, so it's valid to
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look at them too. */
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{
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bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
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if (SYSCALL_RESOLUTION == BILLION)
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{
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if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
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res = BILLION;
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}
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else
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{
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int a = dst_a_ns;
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int c = dst_c_ns;
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int m = dst_m_ns;
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/* Write it this way to avoid mistaken GCC warning
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about integer overflow in constant expression. */
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int SR10 = SYSCALL_RESOLUTION; SR10 *= 10;
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if ((a % SR10 | c % SR10 | m % SR10) != 0)
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res = SYSCALL_RESOLUTION;
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else
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for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
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(res < dst_res->resolution
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&& (a % 10 | c % 10 | m % 10) == 0);
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res *= 10, a /= 10, c /= 10, m /= 10)
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if (res == BILLION)
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{
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if (! odd_second)
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res *= 2;
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break;
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}
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}
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dst_res->resolution = res;
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}
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if (SYSCALL_RESOLUTION < res)
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{
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struct timespec timespec[2];
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struct stat dst_status;
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/* Ignore source time stamp information that must necessarily
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be lost when filtered through utimens. */
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src_ns -= src_ns % SYSCALL_RESOLUTION;
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/* If the time stamps disagree widely enough, there's no need
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to interrogate the file system to deduce the exact time
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stamp resolution; return the answer directly. */
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{
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time_t s = src_s & ~ (res == 2 * BILLION);
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if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
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return 1;
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if (dst_s < s
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|| (dst_s == s && dst_ns < src_ns - src_ns % res))
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return -1;
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}
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/* Determine the actual time stamp resolution for the
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destination file system (after truncation due to
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SYSCALL_RESOLUTION) by setting the access time stamp of the
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destination to the existing access time, except with
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trailing nonzero digits. */
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timespec[0].tv_sec = dst_a_s;
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timespec[0].tv_nsec = dst_a_ns;
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timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
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timespec[1].tv_nsec = dst_m_ns + res / 9;
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/* Set the modification time. But don't try to set the
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modification time of symbolic links; on many hosts this sets
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the time of the pointed-to file. */
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if (S_ISLNK (dst_stat->st_mode)
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|| utimens (dst_name, timespec) != 0)
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return -2;
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/* Read the modification time that was set. It's safe to call
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'stat' here instead of worrying about 'lstat'; either the
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caller used 'stat', or the caller used 'lstat' and found
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something other than a symbolic link. */
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{
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int stat_result = stat (dst_name, &dst_status);
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if (stat_result
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| (dst_status.st_mtime ^ dst_m_s)
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| (TIMESPEC_NS (dst_status.st_mtim) ^ dst_m_ns))
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{
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/* The modification time changed, or we can't tell whether
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it changed. Change it back as best we can. */
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timespec[1].tv_sec = dst_m_s;
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timespec[1].tv_nsec = dst_m_ns;
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utimens (dst_name, timespec);
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}
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if (stat_result != 0)
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return -2;
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}
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/* Determine the exact resolution from the modification time
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that was read back. */
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{
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int old_res = res;
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int a = (BILLION * (dst_status.st_mtime & 1)
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+ TIMESPEC_NS (dst_status.st_mtim));
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res = SYSCALL_RESOLUTION;
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for (a /= res; a % 10 != 0; a /= 10)
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{
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if (res == BILLION)
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{
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res *= 2;
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break;
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}
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res *= 10;
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if (res == old_res)
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break;
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}
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}
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}
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dst_res->resolution = res;
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dst_res->exact = true;
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}
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/* Truncate the source's time stamp according to the resolution. */
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src_s &= ~ (res == 2 * BILLION);
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src_ns -= src_ns % res;
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}
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/* Compare the time stamps and return -1, 0, 1 accordingly. */
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return (dst_s < src_s ? -1
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: dst_s > src_s ? 1
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: dst_ns < src_ns ? -1
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: dst_ns > src_ns);
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}
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