lib: Add API for checking out commits into an composefs image

This supports checking out one or more commits into a combined tree
which is then converted into a composefs image containing fs-verity
digests for all the regular files, and payloads that are relative
to a the `repo/objects` directory of a bare ostree repo.

Makefile-libostree.am

@@ -185,12 +185,12 @@ EXTRA_DIST += \
 	$(top_srcdir)/src/libostree/libostree-released.sym \
 	$(NULL)
 
-libostree_1_la_CFLAGS = $(AM_CFLAGS) -I$(srcdir)/bsdiff -I$(srcdir)/libglnx -I$(srcdir)/src/libotutil -I$(srcdir)/src/libostree -I$(builddir)/src/libostree \
+libostree_1_la_CFLAGS = $(AM_CFLAGS) -I$(srcdir)/bsdiff -I$(srcdir)/libglnx -I$(srcdir)/src/libotutil -I$(srcdir)/src/libostree -I$(builddir)/src/libostree  -I$(srcdir)/composefs \
 	$(OT_INTERNAL_GIO_UNIX_CFLAGS) $(OT_INTERNAL_GPGME_CFLAGS) $(OT_DEP_LZMA_CFLAGS) $(OT_DEP_ZLIB_CFLAGS) $(OT_DEP_CRYPTO_CFLAGS) \
 	-fvisibility=hidden '-D_OSTREE_PUBLIC=__attribute__((visibility("default"))) extern' \
 	-DPKGLIBEXECDIR=\"$(pkglibexecdir)\"
 libostree_1_la_LDFLAGS = -version-number 1:0:0 -Bsymbolic-functions $(addprefix $(wl_versionscript_arg),$(symbol_files))
-libostree_1_la_LIBADD = libotutil.la libglnx.la libbsdiff.la $(OT_INTERNAL_GIO_UNIX_LIBS) $(OT_INTERNAL_GPGME_LIBS) \
+libostree_1_la_LIBADD = libcomposefs.la libotutil.la libglnx.la libbsdiff.la $(OT_INTERNAL_GIO_UNIX_LIBS) $(OT_INTERNAL_GPGME_LIBS) \
                         $(OT_DEP_LZMA_LIBS) $(OT_DEP_ZLIB_LIBS) $(OT_DEP_CRYPTO_LIBS)
 # Some change between rust-1.21.0-1.fc27 and rust-1.22.1-1.fc27.x86_64
 libostree_1_la_LIBADD += $(bupsplitpath)

src/libostree/libostree-devel.sym

@@ -23,6 +23,12 @@
 LIBOSTREE_2022.5 {
 global:
   ostree_kernel_args_append_if_missing;
+  ostree_composefs_target_get_type;
+  ostree_composefs_target_new;
+  ostree_composefs_target_ref;
+  ostree_composefs_target_unref;
+  ostree_composefs_target_write_at;
+  ostree_repo_checkout_composefs;
 } LIBOSTREE_2022.4;
 
 /* Stub section for the stable release *after* this development one; don't

src/libostree/ostree-autocleanups.h

@@ -70,6 +70,7 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderMount, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderOverride, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderResult, ostree_repo_finder_result_free)
 G_DEFINE_AUTO_CLEANUP_FREE_FUNC (OstreeRepoFinderResultv, ostree_repo_finder_result_freev, NULL)
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeComposefsTarget, ostree_composefs_target_unref)
 
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeSign, g_object_unref)
 #endif