ln: --relative: fix updating of existing symlinks

Don't dereference an existing symlink being replaced.
I.E. generate the symlink relative to the symlink's containing dir,
rather than to some arbitrary place it points to.

* src/ln.c (convert_abs_rel): Don't consider the final component
of the symlink name when canonicalizing, as we want to avoid
dereferencing the final component.
* tests/ln/relative.sh: Add a test case.
* NEWS: Mention the fix.
Resolves http://bugs.gnu.org/14116

diff --git a/NEWS b/NEWS
index 0c2daad3eccbcc20b850ade7218aafd0360f9fd0..b9fc6d2d99557599f90c7b6f2f3fd8b32aa00dcc 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   permissions.
   [This bug was present in "the beginning".]
 
+  ln --relative now updates existing symlinks correctly.  Previously it based
+  the relative link on the dereferenced path of an existing link.
+  [This bug was introduced when --relative was added in coreutils-8.16.]
+
 ** New features
 
   join accepts a new option: --zero-terminated (-z). As with the sort,uniq

diff --git a/src/ln.c b/src/ln.c
index 1aa14732447e2b0936be1af4cded181261ba4c91..2489b9ac7ff16e8477df8c22993b5fff9ca68b5d 100644 (file)
--- a/src/ln.c
+++ b/src/ln.c
@@ -132,22 +132,24 @@ target_directory_operand (char const *file)
 static char *
 convert_abs_rel (const char *from, const char *target)
 {
-  char *realtarget = canonicalize_filename_mode (target, CAN_MISSING);
+  /* Get dirname to generate paths relative to.  We don't resolve
+     the full TARGET as the last component could be an existing symlink.  */
+  char *targetdir = dir_name (target);
+
+  char *realdest = canonicalize_filename_mode (targetdir, CAN_MISSING);
   char *realfrom = canonicalize_filename_mode (from, CAN_MISSING);
 
   /* Write to a PATH_MAX buffer.  */
   char *relative_from = xmalloc (PATH_MAX);
 
-  /* Get dirname to generate paths relative to.  */
-  realtarget[dir_len (realtarget)] = '\0';
-
-  if (!relpath (realfrom, realtarget, relative_from, PATH_MAX))
+  if (!relpath (realfrom, realdest, relative_from, PATH_MAX))
     {
       free (relative_from);
       relative_from = NULL;
     }
 
-  free (realtarget);
+  free (targetdir);
+  free (realdest);
   free (realfrom);
 
   return relative_from ? relative_from : xstrdup (from);

diff --git a/tests/ln/relative.sh b/tests/ln/relative.sh
index 0418b8a046f112d40935b85e2d4c9bbc781825bc..818da8392d1b41e65a2dbf66cea94bc824ea4ddd 100755 (executable)
--- a/tests/ln/relative.sh
+++ b/tests/ln/relative.sh
@@ -29,4 +29,9 @@ test $(readlink usr/bin/foo) = '../lib/foo/foo' || fail=1
 ln -sr usr/bin/foo usr/lib/foo/link-to-foo
 test $(readlink usr/lib/foo/link-to-foo) = 'foo' || fail=1
 
+# Correctly update an existing link, which was broken in <= 8.21
+ln -s dir1/dir2/f existing_link
+ln -srf here existing_link
+test $(readlink existing_link) = 'here' || fail=1
+
 Exit $fail