install/ostree: Set zipl as the bootloader for s390x

`zipl` cannot dynamically read BLS config at boot, and requires the MBR
to be updated before. So we set `zipl` as the bootloader for s390x by
default. Otherwise, s390x systems cannot reboot into new deployments.

We set the ostree parameter after the initial ostree deployement because
it fails if called during it.
See https://github.com/coreos/coreos-assembler/blob/99bb23e7dfbfa8f1ae8b9bfaca9ff2e6d98c6cba/src/osbuild-manifests/build.common.ipp.yaml#L160-L163

Fixes #2151
Signed-off-by: jbtrystram <jbtrystram@redhat.com>

Author: jbtrystram

crates/lib/src/install.rs

@@ -2053,6 +2053,24 @@ async fn install_to_filesystem_impl(
         }
     } else {
         ostree_install(state, rootfs, cleanup).await?;
+
+        // For s390x, we set zipl as the bootloader
+        // this needs to be done after the ostree commit is deployed,
+        // as we don't want zipl to run during the initial ostree deployement.
+        if cfg!(target_arch = "s390x") {
+            Command::new("ostree")
+                .args([
+                    "config",
+                    "--repo",
+                    "ostree/repo",
+                    "set",
+                    "sysroot.bootloader",
+                    "zipl",
+                ])
+                .cwd_dir(rootfs.physical_root.try_clone()?)
+                .run_capture_stderr()
+                .context("Setting bootloader config to zipl")?;
+        }
     }
 
     // As the very last step before filesystem finalization, do a full SELinux