bootloader/grub2: Don't do anything if we have static configs

This builds on top of coreos/bootupd@fa9924e
(But in a very hacky way because we don't currently link to a JSON library)

Basically, bootupd supports injecting static configs, and this
is the currently least hacky way for us to detect this and understand
that we shouldn't try to run `grub2-mkconfig`.

A further patch I'd like to do here is also change the probing
logic to gracefully no-op if `grub2-mkconfig` doesn't exist,
but that has a bit more risk and involvement.

src/libostree/ostree-bootloader-grub2.c

@@ -26,6 +26,11 @@
 
 #include <string.h>
 
+// Written by bootupd
+#define BOOTUPD_CONFIG "boot/bootupd-state.json"
+// Horrible hack, to avoid including a JSON parser we just grep for this
+#define BOOTUPD_CONFIG_STATIC_JSON_FRAGMENT "\"static-configs\""
+
 /* Maintain backwards compatibility with legacy GRUB
  * installations that might rely on the -16 suffix
  * for real-mode booting.
@@ -75,6 +80,22 @@ _ostree_bootloader_grub2_query (OstreeBootloader *bootloader, gboolean *out_is_a
 {
   OstreeBootloaderGrub2 *self = OSTREE_BOOTLOADER_GRUB2 (bootloader);
 
+  g_autoptr (GFile) bootupd_config
+      = g_file_resolve_relative_path (self->sysroot->path, BOOTUPD_CONFIG);
+  if (g_file_query_exists (bootupd_config, NULL))
+    {
+      g_autofree char *bootupd_config_contents = NULL;
+      if (!g_file_load_contents (bootupd_config, cancellable, &bootupd_config_contents, NULL, NULL,
+                                 error))
+        return glnx_prefix_error (error, "Failed to read bootupd config");
+      if (strstr (bootupd_config_contents, BOOTUPD_CONFIG_STATIC_JSON_FRAGMENT) != NULL)
+        {
+          g_debug ("Found static bootupd config");
+          *out_is_active = FALSE;
+          return TRUE;
+        }
+    }
+
   /* Look for the BIOS path first */
   if (g_file_query_exists (self->config_path_bios_1, NULL)
       || g_file_query_exists (self->config_path_bios_2, NULL))

tests/kolainst/destructive/bootupd-static.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+set -xeuo pipefail
+
+. ${KOLA_EXT_DATA}/libinsttest.sh
+
+require_writable_sysroot
+prepare_tmpdir
+
+bootupd_state=/boot/bootupd-state.json
+mount -o remount,rw /boot
+if grep -qFe "\"static-configs\"" "${bootupd_state}"; then
+    echo "Host is using static configs already, overriding this"
+    jq 'del(.["static-configs"])' < "${bootupd_state}" > "${bootupd_state}".new
+    mv "${bootupd_state}.new" "${bootupd_state}"
+fi
+
+# Print the current value for reference, it's "none" on FCOS derivatives
+ostree config get sysroot.bootloader || true
+ostree config set sysroot.bootloader auto
+
+ostree admin deploy --stage "${host_commit}"
+systemctl stop ostree-finalize-staged.service
+used_bootloader=$(journalctl -u ostree-finalize-staged -o json MESSAGE_ID=dd440e3e549083b63d0efc7dc15255f1 | tail -1 | jq -r .OSTREE_BOOTLOADER)
+# We're verifying the legacy default now
+assert_streq "${used_bootloader}" "grub2"
+ostree admin undeploy 0
+
+# Now synthesize a bootupd config which uses static configs
+jq '. + {"static-configs": {}}' < "${bootupd_state}"  > "${bootupd_state}".new
+mv "${bootupd_state}.new" "${bootupd_state}"
+ostree admin deploy --stage "${host_commit}"
+systemctl stop ostree-finalize-staged.service
+used_bootloader=$(journalctl -u ostree-finalize-staged -o json MESSAGE_ID=dd440e3e549083b63d0efc7dc15255f1 | tail -1 | jq -r .OSTREE_BOOTLOADER)
+assert_streq "${used_bootloader}" "none"
+
+echo "ok bootupd static"