Subject: bug#15173: [PATCH] cp: with --link always use linkat() if available

From: Pádraig Brady <[email-masked]>
Date: Thu, 12 Dec 2013 18:44:15 +0000

On 12/09/2013 02:24 AM, Pádraig Brady wrote:
> Sorry if you get multiple copies of this.
> 
> The test for this is failing on solaris 10 (NFS)
> It does seem that hardlinks to symlinks are supported:
> 
> $ touch tfile
> $ ln -s tfile tlink
> $ src/ln -L tlink tlink-ln-L
> $ src/ln -P tlink tlink-ln-P
> $ src/ln tlink tlink-ln
> $ ls -li tfile tlink*
>       8550 -rw-r--r--   3 padraig  csw            0 Dec  9 01:18 tfile
>       8551 lrwxrwxrwx   2 padraig  csw            5 Dec  9 01:19 tlink -> tfile
>       8550 -rw-r--r--   3 padraig  csw            0 Dec  9 01:18 tlink-ln
>       8550 -rw-r--r--   3 padraig  csw            0 Dec  9 01:18 tlink-ln-L
>       8551 lrwxrwxrwx   2 padraig  csw            5 Dec  9 01:19 tlink-ln-P -> tfile
> 
> But we have linkat() emulation in place I think:
> 
> $ grep LINK lib/config.h
...
> /* #undef HAVE_LINKAT */
> #define LINK_FOLLOWS_SYMLINKS -1

> FAIL: tests/cp/link-deref
> =========================

> --- exp	Mon Dec  9 01:00:08 2013
> +++ out	Mon Dec  9 01:00:08 2013
> @@ -1,1 +1,1 @@
> -cp --link -P  dirlink dst|result=0|inode=8436|type=symbolic link|error=
> +cp --link -P  dirlink dst|result=0|inode=8467|type=symbolic link|error=
> + rm -f diff.out
> + false
> + ls -lid dirlink dir dst
> 8434 drwxr-xr-x 2 padraig csw 2 Dec  9 01:00 dir
> 8436 lrwxrwxrwx 1 padraig csw 3 Dec  9 01:00 dirlink -> dir
> 8467 lrwxrwxrwx 1 padraig csw 3 Dec  9 01:00 dst -> dir
> + fail=1

So the attached should address this on FreeBSD ast least
where we HAVE_LINKAT so don't need to fallback to
the symlink -> symlink emulation in copy.c

For the above case we'll need to skip parts of the test I think,
depending on the above 2 config vars.

thanks,
Pádraig
>From 3cc98a94d79c2f46f0c0bb70007987f377a65c83 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A1draig=20Brady?= <[email-masked]>
Date: Thu, 12 Dec 2013 18:31:48 +0000
Subject: [PATCH] cp: with --link always use linkat() if available

* src/copy.c (copy_reg): If linkat() is available it doesn't
matter about the gnulib emulation provided, and thus the
LINK_FOLLOWS_SYMLINKS should not have significance here.
This was noticed on FreeBSD and the consequence is that
cp --link will create hardlinks to symlinks there, rather
than emulating with symlinks to symlinks.
---
 src/copy.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/copy.c b/src/copy.c
index 0f044d0..3f148f1 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -2481,8 +2481,11 @@ copy_internal (char const *src_name, char const *dst_name,
      timestamps or ownership so we only call it when we know the
      emulation will not be needed.  */
   else if (x->hard_link
+#if ! defined HAVE_LINKAT
            && !(LINK_FOLLOWS_SYMLINKS && S_ISLNK (src_mode)
-                && x->dereference == DEREF_NEVER))
+                && x->dereference == DEREF_NEVER)
+#endif
+          )
     {
       if (! create_hard_link (src_name, dst_name, false, false, dereference))
         goto un_backup;
@@ -2621,8 +2624,11 @@ copy_internal (char const *src_name, char const *dst_name,
   /* If we've just created a hard-link due to cp's --link option,
      we're done.  */
   if (x->hard_link && ! S_ISDIR (src_mode)
+#if ! defined HAVE_LINKAT
       && !(LINK_FOLLOWS_SYMLINKS && S_ISLNK (src_mode)
-           && x->dereference == DEREF_NEVER))
+           && x->dereference == DEREF_NEVER)
+#endif
+     )
     return delayed_ok;
 
   if (copied_as_regular)
-- 
1.7.7.6