core: Use source root for repos and dnf vars

The goal here is to have the new (more container-native) flow
for `experimental compose rootfs` to always operate on a "repos container"
that we've mounted.

I noticed that `rpmostree_find_and_download_packages()` has
similar behavior, but that's apparently only used in override
flows?

The only ugly workaround we need now is for the rpm-gpg stuff.

Signed-off-by: Colin Walters <[email protected]>

Author: cgwalters

src/app/rpmostree-compose-builtin-tree.cxx

@@ -297,6 +297,13 @@ set_repos_dir (DnfContext *dnfctx, rpmostreecxx::Treefile &treefile, int workdir
   if (!repovars.empty ())
     g_ptr_array_add (var_dirs, (char *)repovars.c_str ());
 
+  g_autofree char *source_vars = NULL;
+  if (opt_source_root)
+    {
+      source_vars = g_build_filename (opt_source_root, "etc/dnf/vars", NULL);
+      g_ptr_array_add (var_dirs, (char*) source_vars);
+    }
+
   g_ptr_array_add (var_dirs, NULL);
   dnf_context_set_vars_dir (dnfctx, (const gchar *const *)var_dirs->pdata);
 

src/libpriv/rpmostree-core.cxx

@@ -668,6 +668,14 @@ rpmostree_context_setup (RpmOstreeContext *self, const char *install_root, const
 
   dnf_context_set_install_root (self->dnfctx, install_root);
   dnf_context_set_source_root (self->dnfctx, source_root);
+  if (source_root)
+    {
+      // Override what rpmostree_context_set_cache_root() did.
+      // TODO disentangle these things so that we only call set_repo_dir if
+      // we didn't have a source root.
+      g_autofree char *source_repos = g_build_filename (source_root, "etc/yum.repos.d", NULL);
+      dnf_context_set_repo_dir (self->dnfctx, source_repos);
+    }
 
   /* Hackaround libdnf logic, ensuring that `/etc/dnf/vars` gets sourced
    * from the host environment instead of the install_root:

tests/compose-rootfs/Containerfile

@@ -1,5 +1,5 @@
-# In theory this can skew from the builder
-FROM quay.io/fedora/fedora:41 as repos
+# Demonstrate skew from the builder
+FROM quay.io/centos/centos:stream10 as repos
 
 # You must run this build with `-v /path/to/rpm-ostree:/run/build/rpm-ostree:ro`
 FROM quay.io/fedora/fedora:41 as builder
@@ -17,12 +17,8 @@ COPY . /src
 WORKDIR /src
 RUN --mount=type=bind,from=repos,src=/,dst=/repos <<EORUN
 set -xeuo pipefail
-# Synchronize the dnf/rpm configs from the repos container.
-for x in etc/dnf etc/yum.repos.d etc/pki/rpm-gpg; do
-  rm -rf /"$x" && cp -a /repos/${x} /$x
-done
-# And copy to the workdir; TODO fix this in rpm-ostree
-cp /etc/yum.repos.d/*.repo .
+# Workaround for https://github.com/coreos/rpm-ostree/issues/5285
+cp -a /repos/etc/pki/rpm-gpg/* /etc/pki/rpm-gpg
 exec rpm-ostree experimental compose rootfs --source-root=/repos manifest.yaml /target-rootfs
 EORUN