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.

NEWS

@@ -13,6 +13,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   printing a summary to stderr.
   [bug introduced in coreutils-6.11]
 
+** New features
+
+  cp --reflink accepts a new "auto" parameter which falls back to
+  a standard copy if creating a copy-on-write clone is not possible.
 
 * Noteworthy changes in release 7.5 (2009-08-20) [stable]
 

doc/coreutils.texi

@@ -7543,15 +7543,31 @@ Also, it is not portable to use @option{-R} to copy symbolic links
 unless you also specify @option{-P}, as @acronym{POSIX} allows
 implementations that dereference symbolic links by default.
 
-@item --reflink
-@opindex --reflink
+@item --reflink[=@var{when}]
+@opindex --reflink[=@var{when}]
+@cindex COW
+@cindex clone
+@cindex copy on write
 Perform a lightweight, copy-on-write (COW) copy.
-Copying with this option can succeed only on some relatively new file systems.
+Copying with this option can succeed only on some file systems.
 Once it has succeeded, beware that the source and destination files
 share the same disk data blocks as long as they remain unmodified.
 Thus, if a disk I/O error affects data blocks of one of the files,
 the other suffers the exact same fate.
 
+The @var{when} value can be one of the following:
+
+@table @samp
+@item always
+The default behavior: if the copy-on-write operation is not supported
+then report the failure for each file and exit with a failure status.
+
+@item auto
+If the copy-on-write operation is not supported then fall back
+to the standard copy behaviour.
+@end table
+
+
 @item --remove-destination
 @opindex --remove-destination
 Remove each existing destination file before attempting to open it

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;
 }
 

src/copy.h

@@ -43,6 +43,19 @@ enum Sparse_type
   SPARSE_ALWAYS
 };
 
+/* Control creation of COW files.  */
+enum Reflink_type
+{
+  /* Default to a standard copy.  */
+  REFLINK_NEVER,
+
+  /* Try a COW copy and fall back to a standard copy.  */
+  REFLINK_AUTO,
+
+  /* Require a COW copy and fail if not available.  */
+  REFLINK_ALWAYS
+};
+
 /* This type is used to help mv (via copy.c) distinguish these cases.  */
 enum Interactive
 {
@@ -73,6 +86,11 @@ enum Dereference_symlink
    || (Mode) == SPARSE_AUTO		\
    || (Mode) == SPARSE_ALWAYS)
 
+# define VALID_REFLINK_MODE(Mode)	\
+  ((Mode) == REFLINK_NEVER		\
+   || (Mode) == REFLINK_AUTO		\
+   || (Mode) == REFLINK_ALWAYS)
+
 /* These options control how files are copied by at least the
    following programs: mv (when rename doesn't work), cp, install.
    So, if you add a new member, be sure to initialize it in
@@ -219,8 +237,8 @@ struct cp_options
      such a symlink) and returns false.  */
   bool open_dangling_dest_symlink;
 
-  /* If true, attempt to clone the file instead of copying it.  */
-  bool reflink;
+  /* Control creation of COW files.  */
+  enum Reflink_type reflink_mode;
 
   /* This is a set of destination name/inode/dev triples.  Each such triple
      represents a file we have created corresponding to a source file name

src/cp.c

@@ -102,6 +102,16 @@ static enum Sparse_type const sparse_type[] =
 };
 ARGMATCH_VERIFY (sparse_type_string, sparse_type);
 
+static char const *const reflink_type_string[] =
+{
+  "auto", "always", NULL
+};
+static enum Reflink_type const reflink_type[] =
+{
+  REFLINK_AUTO, REFLINK_ALWAYS
+};
+ARGMATCH_VERIFY (reflink_type_string, reflink_type);
+
 static struct option const long_opts[] =
 {
   {"archive", no_argument, NULL, 'a'},
@@ -122,7 +132,7 @@ static struct option const long_opts[] =
   {"recursive", no_argument, NULL, 'R'},
   {"remove-destination", no_argument, NULL, UNLINK_DEST_BEFORE_OPENING},
   {"sparse", required_argument, NULL, SPARSE_OPTION},
-  {"reflink", no_argument, NULL, REFLINK_OPTION},
+  {"reflink", optional_argument, NULL, REFLINK_OPTION},
   {"strip-trailing-slashes", no_argument, NULL, STRIP_TRAILING_SLASHES_OPTION},
   {"suffix", required_argument, NULL, 'S'},
   {"symbolic-link", no_argument, NULL, 's'},
@@ -192,12 +202,12 @@ Mandatory arguments to long options are mandatory for short options too.\n\
 "), stdout);
       fputs (_("\
   -R, -r, --recursive          copy directories recursively\n\
-      --reflink                perform a lightweight (CoW/clone) copy\n\
+      --reflink[=WHEN]         control clone/CoW copies. See below.\n\
       --remove-destination     remove each existing destination file before\n\
                                  attempting to open it (contrast with --force)\n\
 "), stdout);
       fputs (_("\
-      --sparse=WHEN            control creation of sparse files\n\
+      --sparse=WHEN            control creation of sparse files. See below.\n\
       --strip-trailing-slashes  remove any trailing slashes from each SOURCE\n\
                                  argument\n\
 "), stdout);
@@ -223,6 +233,10 @@ corresponding DEST file is made sparse as well.  That is the behavior\n\
 selected by --sparse=auto.  Specify --sparse=always to create a sparse DEST\n\
 file whenever the SOURCE file contains a long enough sequence of zero bytes.\n\
 Use --sparse=never to inhibit creation of sparse files.\n\
+\n\
+When --reflink[=always] is specified, perform a lightweight copy, where the\n\
+data blocks are copied only when modified.  If this is not possible the copy\n\
+fails, or if --reflink=auto is specified, fall back to a standard copy.\n\
 "), stdout);
       fputs (_("\
 \n\
@@ -755,7 +769,7 @@ cp_option_init (struct cp_options *x)
   x->interactive = I_UNSPECIFIED;
   x->move_mode = false;
   x->one_file_system = false;
-  x->reflink = false;
+  x->reflink_mode = REFLINK_NEVER;
 
   x->preserve_ownership = false;
   x->preserve_links = false;
@@ -921,7 +935,11 @@ main (int argc, char **argv)
           break;
 
         case REFLINK_OPTION:
-          x.reflink = true;
+          if (optarg == NULL)
+            x.reflink_mode = REFLINK_ALWAYS;
+          else
+            x.reflink_mode = XARGMATCH ("--reflink", optarg,
+                                       reflink_type_string, reflink_type);
           break;
 
         case 'a':		/* Like -dR --preserve=all with reduced failure diagnostics. */
@@ -1084,7 +1102,7 @@ main (int argc, char **argv)
       usage (EXIT_FAILURE);
     }
 
-  if (x.reflink && x.sparse_mode != SPARSE_AUTO)
+  if (x.reflink_mode == REFLINK_ALWAYS && x.sparse_mode != SPARSE_AUTO)
     {
       error (0, 0, _("--reflink can be used only with --sparse=auto"));
       usage (EXIT_FAILURE);

src/install.c

@@ -269,7 +269,7 @@ cp_option_init (struct cp_options *x)
 {
   cp_options_default (x);
   x->copy_as_regular = true;
-  x->reflink = false;
+  x->reflink_mode = REFLINK_NEVER;
   x->dereference = DEREF_ALWAYS;
   x->unlink_dest_before_opening = true;
   x->unlink_dest_after_failed_open = false;

src/mv.c

@@ -105,7 +105,7 @@ cp_option_init (struct cp_options *x)
 
   cp_options_default (x);
   x->copy_as_regular = false;  /* FIXME: maybe make this an option */
-  x->reflink = false;
+  x->reflink_mode = REFLINK_NEVER;
   x->dereference = DEREF_NEVER;
   x->unlink_dest_before_opening = false;
   x->unlink_dest_after_failed_open = false;

tests/Makefile.am

@@ -291,6 +291,7 @@ TESTS =						\
   cp/proc-short-read				\
   cp/proc-zero-len				\
   cp/r-vs-symlink				\
+  cp/reflink-auto				\
   cp/same-file					\
   cp/slink-2-slink				\
   cp/sparse					\

tests/cp/reflink-auto

@@ -0,0 +1,45 @@
+#!/bin/sh
+# Test cp --reflink=auto
+
+# Copyright (C) 2009 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  cp --version
+fi
+
+. $srcdir/test-lib.sh
+
+cleanup_() { rm -rf "$other_partition_tmpdir"; }
+. "$abs_srcdir/other-fs-tmpdir"
+a_other="$other_partition_tmpdir/a"
+rm -f $a_other || framework_failure
+
+echo non_zero_size > "$a_other"
+
+# we shouldn't be able to reflink() files on separate partitions
+cp --reflink      "$a_other" b && fail=1
+
+# --reflink=auto should fall back to a normal copy
+cp --reflink=auto "$a_other" b || fail=1
+test -s b || fail=1
+
+# --reflink=auto should allow --sparse for fallback copies.
+# This command can be used to create minimal sized copies.
+cp --reflink=auto --sparse=always "$a_other" b || fail=1
+test -s b || fail=1
+
+Exit $fail