lib/commit: Implement "adoption" with CONSUME flag

For checkouts that are on the same device, for regular files we can simply
"adopt" existing files. This is useful in the "build from subtrees" pattern that
happens with e.g. `rpm-ostree install` as well as flatpak and gnome-continuous.

New files are things like an updated `ldconfig` cache, etc. And particularly for
`rpm-ostree` we always regenerate the rpmdb, which for e.g. this workstation is
`61MB`.

We probably should have done this from the start, and instead had a `--copy`
flag to commit, but obviously we have to be backwards compatible.

There's more to do here - the biggest gap is probably for `bare-user` repos,
which are often used with things like `rpm-ostree compose tree` for host
systems. But we can do that later.

Closes: #1272
Approved by: jlebon

tests/basic-test.sh

@@ -19,7 +19,7 @@
 
 set -euo pipefail
 
-echo "1..$((76 + ${extra_basic_tests:-0}))"
+echo "1..$((77 + ${extra_basic_tests:-0}))"
 
 CHECKOUT_U_ARG=""
 CHECKOUT_H_ARGS="-H"
@@ -186,8 +186,34 @@ assert_not_has_dir $test_tmpdir/checkout-test2-l
 $OSTREE fsck
 # Some of the later tests are sensitive to state
 $OSTREE reset test2 test2^
+$OSTREE prune --refs-only
 echo "ok consume (nom nom nom)"
 
+# Test adopt
+cd ${test_tmpdir}
+rm checkout-test2-l -rf
+$OSTREE checkout ${CHECKOUT_H_ARGS} test2 $test_tmpdir/checkout-test2-l
+echo 'a file to consume 🍔' > $test_tmpdir/checkout-test2-l/eatme.txt
+# Save a link to it for device/inode comparison
+ln $test_tmpdir/checkout-test2-l/eatme.txt $test_tmpdir/eatme-savedlink.txt
+$OSTREE commit ${COMMIT_ARGS} --link-checkout-speedup --consume -b test2 --tree=dir=$test_tmpdir/checkout-test2-l
+$OSTREE fsck
+# Adoption isn't implemented for bare-user yet
+eatme_objpath=$(ostree_file_path_to_object_path repo test2 /eatme.txt)
+if grep -q '^mode=bare$' repo/config || is_bare_user_only_repo repo; then
+    assert_files_hardlinked ${test_tmpdir}/eatme-savedlink.txt ${eatme_objpath}
+else
+    if files_are_hardlinked ${test_tmpdir}/eatme-savedlink.txt ${eatme_objpath}; then
+        fatal "bare-user adopted?"
+    fi
+fi
+assert_not_has_dir $test_tmpdir/checkout-test2-l
+# Some of the later tests are sensitive to state
+$OSTREE reset test2 test2^
+$OSTREE prune --refs-only
+rm -f ${test_tmpdir}/eatme-savedlink.txt
+echo "ok adopt"
+
 cd ${test_tmpdir}
 $OSTREE commit ${COMMIT_ARGS} -b test2-no-parent -s '' $test_tmpdir/checkout-test2-4
 assert_streq $($OSTREE log test2-no-parent |grep '^commit' | wc -l) "1"