Re: [coreutils] cp/reflink-perm fails on btrfs (and probably on ocfs2, too)

[Jim Meyering]

Erik Auerswald wrote:

> Hi,
>
> On Tue, Oct 26, 2010 at 11:39:58AM +0200, Jim Meyering wrote:
>> The cp/reflink-perm test fails on a btrfs file system:
>>
>>     echo > file2 # file with data
>>     cp --reflink=auto --preserve --attributes-only file2 empty_copy || fail=1
>>     test -s empty_copy && fail=1
>>
>> because with --reflink=auto, the file contents are copied, too,
>
> Is this intentional? I would have expected that no data is copied, because
> this is stated in the documentation. The --reflink option should change
> behaviour of a data copy only, IMHO.

Thanks for the feedback.

I wondered the same thing and looked at this part of copy.c,
but I didn't look carefully enough.

[data_copy_required defaults to true, but is set to false
 with --attributes-only ]

  if (x->reflink_mode)
    {
      bool clone_ok = clone_file (dest_desc, source_desc) == 0;
      if (clone_ok || x->reflink_mode == REFLINK_ALWAYS)
        {
          if (!clone_ok)
            {
              error (0, errno, _("failed to clone %s"), quote (dst_name));
              return_val = false;
              goto close_src_and_dst_desc;
            }
          data_copy_required = false;
        }
    }

Now, I think you're right.
Perhaps, with --attributes-only cp should not even attempt
the reflink copy, like this:

diff --git a/src/copy.c b/src/copy.c
index df31592..f49722f 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -622,7 +622,7 @@ copy_reg (char const *src_name, char const *dst_name,
       goto close_src_and_dst_desc;
     }

-  if (x->reflink_mode)
+  if (data_copy_required && x->reflink_mode)
     {
       bool clone_ok = clone_file (dest_desc, source_desc) == 0;
       if (clone_ok || x->reflink_mode == REFLINK_ALWAYS)

Writing that makes me think that the combination
of --attributes-only and --reflink=ANYTHING (or --reflink)
should elicit an error.