commit: add logic for .payload-link

When a new object is added to the repository, create a
$PAYLOAD-SHA256.payload-link symlink file as well.  The target of the
symlink is the checksum of the object that was added the repository.

Whenever we add a new object file, in addition to lookup if the file is
already present with the same checksum we also check if an object with
the same payload is in the repository.

If a file with the same payload is already present in the repository, we
copy it with `glnx_regfile_copy_bytes` that internally attempts to
create a reflink (ioctl (..., FICLONE, ..)) to the target file if the
file system supports it.  This enables to have objects that share the
payload but have a different inode and xattrs.

By default the payload-link-threshold value is G_MAXUINT64 that disables
the feature.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

Closes: #1443
Approved by: cgwalters

tests/installed/itest-payload-link.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+#
+# Copyright (C) 2018 Red Hat, Inc.
+#
+# SPDX-License-Identifier: LGPL-2.0+
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2 of the License, or (at your option) any later version.
+#
+# This library 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
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the
+# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+# Boston, MA 02111-1307, USA.
+
+set -xeuo pipefail
+
+dn=$(dirname $0)
+. ${dn}/libinsttest.sh
+
+echo "1..1"
+
+cd /var/srv
+mkdir repo
+ostree --repo=repo init --mode=archive
+echo -e '[archive]\nzlib-level=1\n' >> repo/config
+host_nonremoteref=$(echo ${host_refspec} | sed 's,[^:]*:,,')
+ostree --repo=repo pull-local /ostree/repo ${host_commit}
+ostree --repo=repo refs ${host_commit} --create=${host_nonremoteref}
+
+run_tmp_webserver $(pwd)/repo
+
+origin=$(cat ${test_tmpdir}/httpd-address)
+
+cleanup() {
+    cd ${oldpwd}
+    umount mnt || true
+    test -n "${blkdev}" && losetup -d ${blkdev} || true
+    rm -rf mnt testblk.img
+}
+oldpwd=`pwd`
+trap cleanup EXIT
+
+mkdir mnt
+truncate -s 2G testblk.img
+if ! blkdev=$(losetup --find --show $(pwd)/testblk.img); then
+    echo "ok # SKIP not run when cannot setup loop device"
+    exit 0
+fi
+
+mkfs.xfs -m reflink=1 ${blkdev}
+
+mount ${blkdev} mnt
+
+test_tmpdir=$(pwd)/mnt
+cd ${test_tmpdir}
+
+touch a
+if cp --reflink a b; then
+    mkdir repo
+    ostree --repo=repo init
+    ostree config --repo=repo set core.payload-link-threshold 0
+    ostree --repo=repo remote add origin --set=gpg-verify=false ${origin}
+    ostree --repo=repo pull --disable-static-deltas origin ${host_nonremoteref}
+    if test `find repo -name '*.payload-link' | wc -l` = 0; then
+        fatal ".payload-link files not found"
+    fi
+
+    find repo -name '*.payload-link' | while read i;
+    do
+        payload_checksum=$(basename $(dirname $i))$(basename $i .payload-link)
+        payload_checksum_calculated=$(sha256sum $(readlink -f $i) | cut -d ' ' -f 1)
+        if test $payload_checksum != $payload_checksum_calculated; then
+            fatal ".payload-link has the wrong checksum"
+        fi
+    done
+    echo "ok pull creates .payload-link"
+else
+    echo "ok # SKIP no reflink support in the file system"
+fi