Jim Meyering <j...@meyering.net> writes:
> I am now convinced that cp's new behavior belongs on
> a separate option, --reflink (i.e., it should not be the default).
> Giuseppe, do you feel like adding that option and adjusting your
> test accordingly?
I attached two separate patches, --reflink option and file-clone test.
Last versions of btrfs have a bug (I asked on #btrfs and they confirmed
it), btrfs doesn't use correctly all the free space available. In fact
I get ENOSPC while in reality only 54% is used. Probably it is better
to postpone the second patch inclusion after the bug is fixed.
Another note, I changed this line in the NEWS file:
- "when both the source and destination are on the same btrfs partition."
considering that BTRFS supports multiple devices I am not convinced that
it is always true, I guess source and destination could be on different
partitions, though I couldn't find a clear answer on the btrfs wiki to
this question.
Any comment?
Thanks,
Giuseppe
>From d110badaf7583acf957477bc7eda2e212b404343 Mon Sep 17 00:00:00 2001
From: Giuseppe Scrivano <gscriv...@gnu.org>
Date: Sat, 1 Aug 2009 19:36:48 +0200
Subject: [PATCH 1/2] cp: accept the --reflink option
* NEWS: Mention it.
* doc/coreutils.texi: Likewise.
* src/copy.h (struct cp_options): New member reflink.
* src/copy.c (usage): Likewise.
(copy_reg): If reflink is true try to clone the file.
(main): Check for --reflink.
(cp_option_init): By default set reflink to false.
---
NEWS | 4 ++--
doc/coreutils.texi | 9 +++++++++
src/copy.c | 5 +++--
src/copy.h | 3 +++
src/cp.c | 10 +++++++++-
5 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/NEWS b/NEWS
index 80c60e2..8d6d7a6 100644
--- a/NEWS
+++ b/NEWS
@@ -35,8 +35,8 @@ GNU coreutils NEWS -*-
outline -*-
chroot now accepts the options --userspec and --groups.
- cp, install, mv: take advantage of btrfs' O(1) copy-on-write feature
- when both the source and destination are on the same btrfs partition.
+ cp accepts a new option, --reflink: attempt a copy-on-write (COW)
+ when the file system supports it.
sort accepts a new option, --human-numeric-sort (-h): sort numbers
while honoring human readable suffixes like KiB and MB etc.
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index acec76e..03c9eb7 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -7543,6 +7543,15 @@ 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
+Attempt a O(1) copy-on-write (COW) when the underlying file system
+supports this operation instead of really copying the file.
+The source and destination files share the same disk data blocks until
+they are equal. Changes done in a file are not visible in the other
+one because shared blocks will be duplicated before these changes are
+stored.
+
@item --remove-destination
@opindex --remove-destination
Remove each existing destination file before attempting to open it
diff --git a/src/copy.c b/src/copy.c
index bbed336..02d36f3 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -610,10 +610,11 @@ copy_reg (char const *src_name, char const *dst_name,
goto close_src_and_dst_desc;
}
- /* If --sparse=auto is in effect, attempt a btrfs clone operation.
+ /* Attempt a clone operation. It is possible only when --sparse=auto
+ is in effect.
If the operation is not supported or it fails then copy the file
in the usual way. */
- bool copied = (x->sparse_mode == SPARSE_AUTO
+ bool copied = (x->reflink && x->sparse_mode == SPARSE_AUTO
&& clone_file (dest_desc, source_desc) == 0);
if (!copied)
diff --git a/src/copy.h b/src/copy.h
index 8e0b408..ddf4f4e 100644
--- a/src/copy.h
+++ b/src/copy.h
@@ -219,6 +219,9 @@ 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;
+
/* 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
that was specified on the command line. Use it to avoid clobbering
diff --git a/src/cp.c b/src/cp.c
index 8785076..63c07d4 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -78,7 +78,8 @@ enum
PRESERVE_ATTRIBUTES_OPTION,
SPARSE_OPTION,
STRIP_TRAILING_SLASHES_OPTION,
- UNLINK_DEST_BEFORE_OPENING
+ UNLINK_DEST_BEFORE_OPENING,
+ REFLINK_OPTION
};
/* True if the kernel is SELinux enabled. */
@@ -121,6 +122,7 @@ 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},
{"strip-trailing-slashes", no_argument, NULL, STRIP_TRAILING_SLASHES_OPTION},
{"suffix", required_argument, NULL, 'S'},
{"symbolic-link", no_argument, NULL, 's'},
@@ -194,6 +196,7 @@ Mandatory arguments to long options are mandatory for short
options too.\n\
attempting to open it (contrast with
--force)\n\
"), stdout);
fputs (_("\
+ --reflink clone the file if it is possible\n\
--sparse=WHEN control creation of sparse files\n\
--strip-trailing-slashes remove any trailing slashes from each SOURCE\n\
argument\n\
@@ -752,6 +755,7 @@ cp_option_init (struct cp_options *x)
x->interactive = I_UNSPECIFIED;
x->move_mode = false;
x->one_file_system = false;
+ x->reflink = false;
x->preserve_ownership = false;
x->preserve_links = false;
@@ -916,6 +920,10 @@ main (int argc, char **argv)
sparse_type_string, sparse_type);
break;
+ case REFLINK_OPTION:
+ x.reflink = true;
+ break;
+
case 'a': /* Like -dR --preserve=all with reduced failure
diagnostics. */
x.dereference = DEREF_NEVER;
x.preserve_links = true;
--
1.6.3.3
>From 5271957a8ff23df273e975033dabaf7b93e2606f Mon Sep 17 00:00:00 2001
From: Giuseppe Scrivano <gscriv...@gnu.org>
Date: Sat, 1 Aug 2009 19:40:09 +0200
Subject: [PATCH 2/2] tests: add new test for copy-on-write (COW) cp support.
* tests/Makefile.am: Consider the new test.
* tests/cp/file-clone: New file.
---
tests/Makefile.am | 1 +
tests/cp/file-clone | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 66 insertions(+), 0 deletions(-)
create mode 100644 tests/cp/file-clone
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 59737a0..9841aa3 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -20,6 +20,7 @@ EXTRA_DIST = \
root_tests = \
chown/basic \
+ cp/file-clone \
cp/cp-a-selinux \
cp/preserve-gid \
cp/special-bits \
diff --git a/tests/cp/file-clone b/tests/cp/file-clone
new file mode 100644
index 0000000..21cb61a
--- /dev/null
+++ b/tests/cp/file-clone
@@ -0,0 +1,65 @@
+#!/bin/sh
+# Make sure file-clone on a btrfs file system works properly.
+
+# 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
+
+require_root_
+require_sparse_support_
+
+cleanup_(){ umount btrfs; }
+
+fail=0
+
+mkfs.btrfs --version || skip_test_ "btrfs userland tools not installed"
+
+# 256MB seems to be the minimum size for a btrfs with default parameters.
+truncate --size=256M btrfs.img || framework_failure
+
+mkfs.btrfs btrfs.img || framework_failure
+mkdir btrfs || framework_failure
+mount -t btrfs -o loop btrfs.img btrfs || framework_failure
+
+echo hello > btrfs/a.test || framework_failure
+cp --reflink btrfs/a.test btrfs/b.test || fail=1
+compare btrfs/a.test btrfs/b.test || fail=1
+
+# Be sure that files are different if one is modified.
+echo hello >> btrfs/a.test
+compare btrfs/a.test btrfs/b.test && fail=1
+
+dd bs=1M count=200 if=/dev/zero of=btrfs/alloc.test || framework_failure
+
+# If the file is cloned, only additional space for metadata is required.
+# Two 200MB files can be present even if the total file system space is 256MB.
+cp --reflink btrfs/alloc.test btrfs/clone.test || fail=1
+rm btrfs/clone.test
+
+# A normal copy should raise ENOSPC.
+cp btrfs/alloc.test btrfs/clone.test && fail=1
+
+# When --sparse={always,never} is used, the file is copied without any cloning.
+# Use --sparse=never to be sure the file is copied without holes and it is not
+# possible since there is not enough free space.
+cp --reflink --sparse=never btrfs/alloc.test btrfs/clone.test && fail=1
+
+Exit $fail
--
1.6.3.3
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