Speed up most calls to 'stat' and 'lstat' on MS-Windows.

 src/w32.c (stat_worker): If w32_stat_get_owner_group is zero, do not
 try to get accurate owner and group information from NT file
 security APIs.  This is to make most callers of 'stat' and
 'lstat', which don't need that information, much faster.
 src/dired.c (Ffile_attributes) [WINDOWSNT]: Set
 w32_stat_get_owner_group to a non-zero value, to request accurate
 owner and group information from 'lstat'.

 nt/inc/sys/stat.h: Declare w32_stat_get_owner_group.

1 files changed, 16 insertions, 1 deletions

diff --git a/src/dired.c b/src/dired.c
index bdb71c46364..85af906c1da 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -895,6 +895,7 @@ so last access time will always be midnight of that day.  */)
   Lisp_Object dirname;
   struct stat sdir;
 #endif /* BSD4_2 */
+  int lstat_result;
 
   /* An array to hold the mode string generated by filemodestring,
      including its terminating space and null byte.  */
@@ -922,7 +923,21 @@ so last access time will always be midnight of that day.  */)
   encoded = ENCODE_FILE (filename);
   UNGCPRO;
 
-  if (lstat (SSDATA (encoded), &s) < 0)
+#ifdef WINDOWSNT
+  /* We usually don't request accurate owner and group info, because
+     it can be very expensive on Windows to get that, and most callers
+     of 'lstat' don't need that.  But here we do want that information
+     to be accurate.  */
+  w32_stat_get_owner_group = 1;
+#endif
+
+  lstat_result = lstat (SSDATA (encoded), &s);
+
+#ifdef WINDOWSNT
+  w32_stat_get_owner_group = 0;
+#endif
+
+  if (lstat_result < 0)
     return Qnil;
 
   values[0] = (S_ISLNK (s.st_mode) ? Ffile_symlink_p (filename)