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From: Dan Grayson <dan AT math DOT uiuc DOT edu>
Subject: Re: untarring symlinks with ../ fails randomly
Date: Wed, 27 Apr 2011 15:50:58 +0000 (UTC)
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Here is a patch to tar that fixes the problem by using mtime instead of ctime.
Yes, it's not a problem with cygwin or tar, but I see no way for users to
figure out, under Windows, which processes are changing the status of their
files.

diff -ur tar-1.25-copy/src/extract.c tar-1.25/src/extract.c
--- tar-1.25-copy/src/extract.c	2010-11-01 15:34:59.000000000 -0500
+++ tar-1.25/src/extract.c	2011-04-27 09:12:58.941555800 -0500
@@ -115,7 +115,10 @@
        other process removes the placeholder.  */
     dev_t dev;
     ino_t ino;
-    struct timespec ctime;
+       /* for cygwin, we use mtime instead of ctime of the 
+	  placeholder, because background processes running
+	  under Windows may change it */
+    struct timespec mtime0;
 
     /* True if the link is symbolic.  */
     bool is_symlink;
@@ -1064,7 +1067,7 @@
       delayed_link_head = p;
       p->dev = st.st_dev;
       p->ino = st.st_ino;
-      p->ctime = get_stat_ctime (&st);
+      p->mtime0 = get_stat_mtime (&st);
       p->is_symlink = is_symlink;
       if (is_symlink)
 	{
@@ -1122,7 +1125,7 @@
 	      if (ds->change_dir == chdir_current
 		  && ds->dev == st1.st_dev
 		  && ds->ino == st1.st_ino
-		  && timespec_cmp (ds->ctime, get_stat_ctime (&st1)) == 0)
+		  && timespec_cmp (ds->mtime0, get_stat_mtime (&st1)) == 0)
 		{
 		  struct string_list *p =  xmalloc (offsetof (struct string_list, string)
 						    + strlen (file_name) + 1);
@@ -1488,7 +1491,7 @@
 	  if (fstatat (chdir_fd, source, &st, AT_SYMLINK_NOFOLLOW) == 0
 	      && st.st_dev == ds->dev
 	      && st.st_ino == ds->ino
-	      && timespec_cmp (get_stat_ctime (&st), ds->ctime) == 0)
+	      && timespec_cmp (get_stat_mtime (&st), ds->mtime0) == 0)
 	    {
 	      /* Unlink the placeholder, then create a hard link if possible,
 		 a symbolic link otherwise.  */



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