Re: Bad cp -a behaviour

[Paul Eggert]

Philip Rowlands <address@hidden> writes:

> I don't know the specs to which GNU cp adheres well enough, but I'd be
> surprised if they mandate a sort routine for recursive copying.

POSIX places no requirement here, since these options are an extension to POSIX.

The GNU documentation says that "-a" implies "--preserve=links" and
that "--preserve-links" means "Preserve in the destination files any
links between corresponding source files."  Here, Tim wants "cp -a"
to preserve in the destination the fact that the source files are
different, even though they are already hard links in the destination.

This sounds reasonable to me, so I installed the following patch.  But
I'd like someone with sharp eyes (Jim? :-) to double-check it.  In
particular, I don't understand what these lines are doing in the
existing code:

                       || (x->dereference == DEREF_NEVER
                           && ! S_ISREG (src_sb.st_mode))))

Why should the behavior differ here merely because the source
is (say) a character special file?


2004-08-11  Paul Eggert  <address@hidden>

        * src/copy.c (copy_internal): When preserving links, unlink
        a destination with link count greater than one.  This is so
        that commands like "cp -a" don't get confused when copying into
        a destination that already contains many hard links.  Problem
        reported by Tim Waugh in:
        http://lists.gnu.org/archive/html/bug-coreutils/2004-08/msg00053.html

Index: src/copy.c
===================================================================
RCS file: /home/eggert/coreutils/cu/src/copy.c,v
retrieving revision 1.170
retrieving revision 1.171
diff -p -u -r1.170 -r1.171
--- src/copy.c  30 Jul 2004 07:51:59 -0000      1.170
+++ src/copy.c  11 Aug 2004 17:19:25 -0000      1.171
@@ -1079,6 +1079,7 @@ copy_internal (const char *src_path, con
            }
          else if (! S_ISDIR (dst_sb.st_mode)
                   && (x->unlink_dest_before_opening
+                      || (x->preserve_links && 1 < dst_sb.st_nlink)
                       || (x->dereference == DEREF_NEVER
                           && ! S_ISREG (src_sb.st_mode))))
            {