From 216777ea1772271eb2dfd8bd802bdb178d2db28f Mon Sep 17 00:00:00 2001
From: Jim Meyering <jim@meyering.net>
Date: Wed, 26 Jun 1996 12:02:02 +0000
Subject: (same_name): New function. (do_link): Use it to test reliably whether
 A and B (from ln --force A B) are hard links to the same file. From Andreas
 Schwab.

---
 src/ln.c | 45 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

(limited to 'src/ln.c')

diff --git a/src/ln.c b/src/ln.c
index e36a3a537..cc4251b61 100644
--- a/src/ln.c
+++ b/src/ln.c
@@ -63,6 +63,7 @@ int symlink ();
     while (0)
 
 char *basename ();
+char *dirname ();
 enum backup_type get_version ();
 int isdir ();
 int yesno ();
@@ -119,6 +120,37 @@ static struct option const long_options[] =
   {NULL, 0, NULL, 0}
 };
 
+/* Check whether SOURCE and DEST point to the same name in the same
+   directory.  */
+
+static int
+same_name (char *source, char *dest)
+{
+  struct stat source_dir_stats;
+  struct stat dest_dir_stats;
+  char *source_dirname, *dest_dirname;
+
+  source_dirname = dirname (source);
+  dest_dirname = dirname (dest);
+  if (source_dirname == NULL || dest_dirname == NULL)
+    error (1, 0, _("virtual memory exhausted"));
+
+  if (stat (source_dirname, &source_dir_stats))
+    /* Shouldn't happen.  */
+    error (1, errno, "%s", source_dirname);
+
+  if (stat (dest_dirname, &dest_dir_stats))
+    /* Shouldn't happen.  */
+    error (1, errno, "%s", dest_dirname);
+
+  free (source_dirname);
+  free (dest_dirname);
+
+  return (source_dir_stats.st_dev == dest_dir_stats.st_dev
+	  && source_dir_stats.st_ino == dest_dir_stats.st_ino
+	  && STREQ (basename (source), basename (dest)));
+}
+
 /* Make a link DEST to the (usually) existing file SOURCE.
    Symbolic links to nonexistent files are allowed.
    If DEST is a directory, put the link to SOURCE in that directory.
@@ -166,12 +198,13 @@ do_link (const char *source, const char *dest)
       && (!symlink || stat (source, &source_stats) == 0)
       && source_stats.st_dev == dest_stats.st_dev
       && source_stats.st_ino == dest_stats.st_ino
-      /* The following is an attempt to detect reliably whether
-	 removing DEST will also remove SOURCE.  It is defeated
-	 by an invocation like `ln -f foo ./foo' when foo has more
-	 than one hard link.  FIXME: if anyone can tell me how to
-	 do this better (yet still reliably), please do.  */
-      && (source_stats.st_nlink == 1 || STREQ (source, dest)))
+      /* The following detects whether removing DEST will also remove
+ 	 SOURCE.  If the file has only one link then both are surely
+ 	 the same link.  Otherwise we check whether they point to the
+ 	 same names in the same directory.  The latter is meaningless
+ 	 when making a symbolic link.  */
+      && (source_stats.st_nlink == 1
+ 	  || (!symlink && same_name (source, dest))))
     {
       error (0, 0, _("`%s' and `%s' are the same file"), source, dest);
       return 1;
-- 
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