Subject: Re: bug#40352: cp -a --attributes-only zeroes a file with more than one link
From: Pádraig Brady <[email-masked]>
To: Matt Kloss <[email-masked]>, [email-masked]
Date: Wed, 1 Apr 2020 13:10:02 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

On 31/03/2020 13:32, Matt Kloss wrote:
>     Hello,
> 
>     When you cp -a --attributes-only a [dest] file which has a more than one
>     “hardlink”, it zeroes the file:

The attached fixes this, which I'll push later.
Marking this as done.
thanks!

Pádraig
From af51efbe11aeba9fc2609dd69d622cc170b484a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A1draig=20Brady?= <[email-masked]>
Date: Wed, 1 Apr 2020 12:51:34 +0100
Subject: [PATCH] cp: ensure --attributes-only doesn't remove files

* src/copy.c (copy_internal): Ensure we don't unlink the destination
unless explicitly requested.
* tests/cp/attr-existing.sh: Add test cases.
* NEWS: Mention the bug fix.
Fixes https://bugs.gnu.org/40352
---
 NEWS                      |  7 +++++++
 src/copy.c                |  9 +++++----
 tests/cp/attr-existing.sh | 21 ++++++++++++++++++---
 3 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/NEWS b/NEWS
index 653e7178b..b8a17c276 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,13 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** Bug fixes
+
+  cp -a --attributes-only now never removes destination files,
+  even if the destination files are hardlinked, or the source
+  is a non regular file.
+  [bug introduced in coreutils-8.6]
+
 ** Changes in behavior
 
   On GNU/Linux systems, ls no longer issues an error message on
diff --git a/src/copy.c b/src/copy.c
index 6e5efc708..54601ce07 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -2211,10 +2211,11 @@ copy_internal (char const *src_name, char const *dst_name,
                    /* 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->dereference == DEREF_NEVER
-                           && ! S_ISREG (src_sb.st_mode))
-                       ))
+                       || (x->data_copy_required
+                           && ((x->preserve_links && 1 < dst_sb.st_nlink)
+                               || (x->dereference == DEREF_NEVER
+                                   && ! S_ISREG (src_sb.st_mode))))
+                      ))
             {
               if (unlink (dst_name) != 0 && errno != ENOENT)
                 {
diff --git a/tests/cp/attr-existing.sh b/tests/cp/attr-existing.sh
index 59ce64183..14fc8445c 100755
--- a/tests/cp/attr-existing.sh
+++ b/tests/cp/attr-existing.sh
@@ -19,11 +19,26 @@
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 print_ver_ cp
 
-printf '1' > file1
-printf '2' > file2
-printf '2' > file2.exp
+printf '1' > file1 || framework_failure_
+printf '2' > file2 || framework_failure_
+printf '2' > file2.exp || framework_failure_
 
 cp --attributes-only file1 file2 || fail=1
 cmp file2 file2.exp || fail=1
 
+# coreutils v8.32 and before would remove destination files
+# if hardlinked or the source was not a regular file.
+ln file2 link2 || framework_failure_
+cp -a --attributes-only file1 file2 || fail=1
+cmp file2 file2.exp || fail=1
+
+ln -s file1 sym1 || framework_failure_
+returns_ 1 cp -a --attributes-only sym1 file2 || fail=1
+cmp file2 file2.exp || fail=1
+
+# One can still force removal though
+cp -a --remove-destination --attributes-only sym1 file2 || fail=1
+test -L file2 || fail=1
+cmp file1 file2 || fail=1
+
 Exit $fail
-- 
2.24.1