install: Query skopeo upfront

If we don't have skopeo on the host (and it turns out the default
Fedora Workstation install has podman but not skopeo) then we only
error out halfway through an install.

Do this upfront to make the error clearer.

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

lib/src/install.rs

@@ -203,6 +203,8 @@ pub(crate) struct State {
     pub(crate) source: SourceInfo,
     /// Force SELinux off in target system
     pub(crate) override_disable_selinux: bool,
+    /// True if the skoepo on host supports containers-storage:
+    pub(crate) skopeo_supports_containers_storage: bool,
     #[allow(dead_code)]
     pub(crate) setenforce_guard: Option<crate::lsm::SetEnforceGuard>,
     pub(crate) config_opts: InstallConfigOpts,
@@ -501,7 +503,7 @@ async fn initialize_ostree_root_from_self(
     };
 
     let mut temporary_dir = None;
-    let src_imageref = if skopeo_supports_containers_storage()? {
+    let src_imageref = if state.skopeo_supports_containers_storage {
         // We always use exactly the digest of the running image to ensure predictability.
         let spec =
             crate::utils::digested_pullspec(&state.source.imageref.name, &state.source.digest);
@@ -792,6 +794,9 @@ async fn prepare_install(
         anyhow::bail!("Cannot install from rootless podman; this command must be run as root");
     }
 
+    let skopeo_supports_containers_storage = skopeo_supports_containers_storage()
+        .context("Failed to run skopeo (it currently must be installed in the host root)")?;
+
     let source = SourceInfo::from_container(&container_info)?;
 
     ensure_var()?;
@@ -815,6 +820,7 @@ async fn prepare_install(
     // combines our command line options along with some bind mounts from the host.
     let state = Arc::new(State {
         override_disable_selinux,
+        skopeo_supports_containers_storage,
         setenforce_guard,
         source,
         config_opts,