mv: never unlink a destination file before calling rename

While cp --preserve=links must unlink certain destination files,
mv must never do that.
* src/copy.c (copy_internal): Pull the '! x->move_mode' test "up",
so it affects the entire condition, and not just DEREF_NEVER mode.
Reported by James Ralston in <http://bugzilla.redhat.com/438076>.
* tests/mv/atomic2: New file.  Test for the above fix.
* tests/mv/Makefile.am (TESTS): Add atomic2.
* NEWS: Mention the bug-fix.
[Bug introduced in 367719ba5f1dbd5e2f7fa2466c441f23f66a7c9e]

5 files changed, 60 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index 948bcede7..93f133123 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   ls no longer segfaults on files in /proc when linked with an older version
   of libselinux.  E.g., ls -l /proc/sys would dereference a NULL pointer.
 
+  mv would mistakenly unlink a destination file before calling rename,
+  when the destination had two or more hard links.  It no longer does that.
+  [bug introduced in coreutils-5.3.0]
+
   "rmdir --ignore-fail-on-non-empty" detects and ignores the failure
   in more cases when a directory is empty.
 
diff --git a/THANKS b/THANKS
index 2a47910c8..186bf5f58 100644
--- a/THANKS
+++ b/THANKS
@@ -220,6 +220,7 @@ James                               james@albion.glarp.com
 James Antill                        jmanti%essex.ac.uk@seralph21.essex.ac.uk
 James Lemley                        James.Lemley@acxiom.com
 James Hunt                          jamesodhunt@hotmail.com
+James Ralston                       ralston@pobox.com
 James Sneeringer                    jvs@ocslink.com
 James Tanis                         jtt@soscorp.com
 James Youngman                      james+usenet@free-lunch.demon.co.uk
diff --git a/src/copy.c b/src/copy.c
index fd31b5c91..208a67413 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -1339,10 +1339,11 @@ copy_internal (char const *src_name, char const *dst_name,
 	      new_dst = true;
 	    }
 	  else if (! S_ISDIR (dst_sb.st_mode)
+		   /* Never unlink dst_name when in move mode.  */
+		   && ! x->move_mode
 		   && (x->unlink_dest_before_opening
 		       || (x->preserve_links && 1 < dst_sb.st_nlink)
-		       || (!x->move_mode
-			   && x->dereference == DEREF_NEVER
+		       || (x->dereference == DEREF_NEVER
 			   && S_ISLNK (src_sb.st_mode))
 		       ))
 	    {
diff --git a/tests/mv/Makefile.am b/tests/mv/Makefile.am
index c1219113e..92ec68e39 100644
--- a/tests/mv/Makefile.am
+++ b/tests/mv/Makefile.am
@@ -1,7 +1,6 @@
 # Make coreutils tests for "mv".			-*-Makefile-*-
 
-# Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
-# Free Software Foundation, Inc.
+# Copyright (C) 1998-2008 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
@@ -17,6 +16,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 TESTS = \
+  atomic2 \
   sticky-to-xpart \
   hard-verbose \
   backup-dir \
diff --git a/tests/mv/atomic2 b/tests/mv/atomic2
new file mode 100755
index 000000000..d1029aa9c
--- /dev/null
+++ b/tests/mv/atomic2
@@ -0,0 +1,50 @@
+#!/bin/sh
+# ensure that mv doesn't first unlink a multi-hard-linked destination
+
+# Copyright (C) 2008 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
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  mv --version
+fi
+
+. $srcdir/../test-lib.sh
+require_strace_
+
+# Before the fix, mv would unnecessarily unlink the destination symlink:
+#   $ rm -f a b b2; touch a b; ln b b2; strace -e unlink /p/bin/mv a b
+#   unlink("b")                             = 0
+#
+# With the fix, it doesn't call unlink:
+#   $ rm -f a b b2; touch a b; ln b b2; strace -e unlink ./mv a b
+#   $
+
+touch a b || framework_failure
+ln b b2 || framework_failure
+
+fail=0
+
+strace -qe unlink mv a b > out 2>&1 || fail=1
+$EGREP 'unlink.*"b"' out && fail=1
+
+# Ensure that the source, "a", is gone.
+ls -dl a > /dev/null 2>&1 && fail=1
+
+# Ensure that the destination, "b", has link count 1.
+n_links=`stat --printf=%h b` || fail=1
+test "$n_links" = 1 || fail=1
+
+(exit $fail); exit $fail