cp: add an option to only copy the file attributes

* src/copy.c (copy_attr): A new function which merges copy_attr_by_fd
and copy_attr_by_name.  Also display all errors when --attributes-only
* src/copy.c (copy_reg): Skip copying the file contents if specified.
Refactor the SELinux error handling code a little and display all
SELinux errors when only copying attributes.
* src/copy.h (struct cp_options): Add a data_copy_required boolean
* src/cp.c (main): Default to copying data but don't if specified
* src/install.c: Default to copying data
* src/mv.c: Likewise
tests/cp/reflink-perm: Add a test to check that --attributes-only
does not copy data
* tests/cp/acl: Likewise. Also refactor to remove redundant
acl manipulation
* doc/coreutils.texi (cp invocation): Describe the new option
* NEWS: Mention the new feature

1 files changed, 9 insertions, 1 deletions

diff --git a/src/cp.c b/src/cp.c
index 035526922..5b14f3a7b 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -72,7 +72,8 @@ struct dir_attr
    non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
 enum
 {
-  COPY_CONTENTS_OPTION = CHAR_MAX + 1,
+  ATTRIBUTES_ONLY_OPTION = CHAR_MAX + 1,
+  COPY_CONTENTS_OPTION,
   NO_PRESERVE_ATTRIBUTES_OPTION,
   PARENTS_OPTION,
   PRESERVE_ATTRIBUTES_OPTION,
@@ -115,6 +116,7 @@ ARGMATCH_VERIFY (reflink_type_string, reflink_type);
 static struct option const long_opts[] =
 {
   {"archive", no_argument, NULL, 'a'},
+  {"attributes-only", no_argument, NULL, ATTRIBUTES_ONLY_OPTION},
   {"backup", optional_argument, NULL, 'b'},
   {"copy-contents", no_argument, NULL, COPY_CONTENTS_OPTION},
   {"dereference", no_argument, NULL, 'L'},
@@ -167,6 +169,7 @@ Mandatory arguments to long options are mandatory for short options too.\n\
 "), stdout);
       fputs (_("\
   -a, --archive                same as -dR --preserve=all\n\
+      --attributes-only        don't copy the file data, just the attributes\n\
       --backup[=CONTROL]       make a backup of each existing destination file\n\
   -b                           like --backup but does not accept an argument\n\
       --copy-contents          copy contents of special files when recursive\n\
@@ -781,6 +784,7 @@ cp_option_init (struct cp_options *x)
   x->reduce_diagnostics = false;
   x->require_preserve_xattr = false;
 
+  x->data_copy_required = true;
   x->require_preserve = false;
   x->recursive = false;
   x->sparse_mode = SPARSE_AUTO;
@@ -962,6 +966,10 @@ main (int argc, char **argv)
             version_control_string = optarg;
           break;
 
+        case ATTRIBUTES_ONLY_OPTION:
+          x.data_copy_required = false;
+          break;
+
         case COPY_CONTENTS_OPTION:
           copy_contents = true;
           break;