cp --reflink: add an "auto" parameter to fall back to a normal copy

* doc/coreutils.texi (cp invocation): Document the new
"auto" and "always" options to --reflink.
* src/copy.c (copy_reg): Fall back to a standard copy
when reflink() is not supported and --reflink=auto specified.
* src/copy.h [struct cp_options] (reflink): Change type s/bool/enum/.
* src/cp.c (usage): Describe the --reflink={always,auto} options
and expand a little on what --reflink does.
(main): parse the new parameters to --reflink and allow all
--sparse options with --reflink=auto.
* src/install.c (cp_option_init): Init the enum instead of bool.
* src/mv.c (cp_option_init): Likewise.
* tests/cp/reflink-auto: A new test for falling back to normal copy.
* tests/Makefile.am: Reference the new test.
* NEWS: Mention the new feature.

1 files changed, 13 insertions, 6 deletions

diff --git a/src/copy.c b/src/copy.c
index 5f84f7e43..17be63e56 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -635,14 +635,18 @@ copy_reg (char const *src_name, char const *dst_name,
       goto close_src_and_dst_desc;
     }
 
-  if (x->reflink)
+  if (x->reflink_mode)
     {
-      if (clone_file (dest_desc, source_desc))
+      bool clone_ok = clone_file (dest_desc, source_desc) == 0;
+      if (clone_ok || x->reflink_mode == REFLINK_ALWAYS)
         {
-          error (0, errno, _("failed to clone %s"), quote (dst_name));
-          return_val = false;
+          if (!clone_ok)
+            {
+              error (0, errno, _("failed to clone %s"), quote (dst_name));
+              return_val = false;
+            }
+          goto close_src_and_dst_desc;
         }
-      goto close_src_and_dst_desc;
     }
 
   {
@@ -2248,8 +2252,11 @@ valid_options (const struct cp_options *co)
   assert (co != NULL);
   assert (VALID_BACKUP_TYPE (co->backup_type));
   assert (VALID_SPARSE_MODE (co->sparse_mode));
+  assert (VALID_REFLINK_MODE (co->reflink_mode));
   assert (!(co->hard_link && co->symbolic_link));
-  assert (!(co->reflink && co->sparse_mode != SPARSE_AUTO));
+  assert (!
+          (co->reflink_mode == REFLINK_ALWAYS
+           && co->sparse_mode != SPARSE_AUTO));
   return true;
 }