utimecmp: support symlink timestamps

Update this module to reflect POSIX 2008:
With pathconf, we can avoid calling utimens.
With utimensat, the system resolution can be 1.
With lutimens, we can determine resolution on symlinks.

* lib/utimecmp.c (utimecmp): Use new interface.  Skip effort of
hashing when possible.  Use pathconf when available.
(SYSCALL_RESOLUTION): Recognize tighter resolution.
* modules/utimecmp (Depends-on): Add lstat.

Signed-off-by: Eric Blake <ebb9@byu.net>

diff --git a/ChangeLog b/ChangeLog
index 39cc9bd..9da56c2 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2009-10-10  Eric Blake  <ebb9@byu.net>
 
+       utimecmp: support symlink timestamps
+       * lib/utimecmp.c (utimecmp): Use new interface.  Skip effort of
+       hashing when possible.  Use pathconf when available.
+       (SYSCALL_RESOLUTION): Recognize tighter resolution.
+       * modules/utimecmp (Depends-on): Add lstat.
+
        utimens: add lutimens interface
        * lib/utimens.c (lutimens): New function.
        * m4/utimens.m4 (gl_UTIMENS): Check for lutimes.

diff --git a/lib/utimecmp.c b/lib/utimecmp.c
index 6a90873..9dcb652 100644 (file)
--- a/lib/utimecmp.c
+++ b/lib/utimecmp.c
@@ -1,6 +1,7 @@
 /* utimecmp.c -- compare file time stamps
 
-   Copyright (C) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+   Copyright (C) 2004, 2005, 2006, 2007, 2009 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
@@ -26,6 +27,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <time.h>
+#include <unistd.h>
+
 #include "hash.h"
 #include "intprops.h"
 #include "stat-time.h"
@@ -42,12 +45,14 @@ enum { 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_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))
+#if HAVE_UTIMENSAT
+enum { SYSCALL_RESOLUTION = 1 };
+#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 };
@@ -100,6 +105,8 @@ dev_info_compare (void const *x, void const *y)
    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
@@ -147,6 +154,16 @@ utimecmp (char const *dst_name,
       /* Time stamp 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;
+
       if (! ht)
        ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
       if (! new_dst_res)
@@ -169,6 +186,19 @@ utimecmp (char const *dst_name,
 
       res = dst_res->resolution;
 
+#ifdef _PC_TIMESTAMP_RESOLUTION
+      /* If the system will tell us the resolution, we're set! */
+      if (! dst_res->exact)
+       {
+         res = pathconf (dst_name, _PC_TIMESTAMP_RESOLUTION);
+         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.
@@ -258,16 +288,16 @@ utimecmp (char const *dst_name,
              /* Set the modification time.  But don't try to set the
                 modification time of symbolic links; on many hosts this sets
                 the time of the pointed-to file.  */
-             if (S_ISLNK (dst_stat->st_mode)
-                 || utimens (dst_name, timespec) != 0)
+             if ((S_ISLNK (dst_stat->st_mode)
+                  ? lutimens (dst_name, timespec)
+                  : utimens (dst_name, timespec)) != 0)
                return -2;
 
-             /* Read the modification time that was set.  It's safe to call
-                'stat' here instead of worrying about 'lstat'; either the
-                caller used 'stat', or the caller used 'lstat' and found
-                something other than a symbolic link.  */
+             /* Read the modification time that was set.  */
              {
-               int stat_result = stat (dst_name, &dst_status);
+               int stat_result = (S_ISLNK (dst_stat->st_mode)
+                                  ? lstat (dst_name, &dst_status)
+                                  : stat (dst_name, &dst_status));
 
                if (stat_result
                    | (dst_status.st_mtime ^ dst_m_s)
@@ -277,7 +307,10 @@ utimecmp (char const *dst_name,
                       it changed.  Change it back as best we can.  */
                    timespec[1].tv_sec = dst_m_s;
                    timespec[1].tv_nsec = dst_m_ns;
-                   utimens (dst_name, timespec);
+                   if (S_ISLNK (dst_stat->st_mode))
+                     lutimens (dst_name, timespec);
+                   else
+                     utimens (dst_name, timespec);
                  }
 
                if (stat_result != 0)

diff --git a/modules/utimecmp b/modules/utimecmp
index 12da25e..238ab30 100644 (file)
--- a/modules/utimecmp
+++ b/modules/utimecmp
@@ -13,6 +13,7 @@ time
 utimens
 xalloc
 intprops
+lstat
 stdbool
 stdint
 verify