krun: Determine flavor from VM config tree

To support other krun flavors in the future, parse which flavor (and by
extension, which handle) should be used before making any libkrun API
calls past libkrun_create_ctx. The correct handle to be used can be
determined before any other subsequent API calls.

Signed-off-by: Tyler Fanelli <tfanelli@redhat.com>

Author: tylerfanelli

src/libcrun/handlers/krun.c

@@ -59,6 +59,8 @@
  */
 #define KRUN_VM_FILE "/.krun_vm.json"
 
+#define KRUN_FLAVOR_SEV "sev"
+
 struct krun_config
 {
   void *handle;
@@ -199,6 +201,50 @@ libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, yajl_val
   return 0;
 }
 
+static int
+libkrun_configure_flavor (void *cookie, yajl_val *config_tree, libcrun_error_t *err)
+{
+  int sev_indicated = 0;
+  const char *path_flavor[] = { "flavor", (const char *) 0 };
+  struct krun_config *kconf = (struct krun_config *) cookie;
+  yajl_val val_flavor = NULL;
+  char *flavor = NULL;
+
+  // Read if the SEV flavor was indicated in the krun VM config.
+  val_flavor = yajl_tree_get (*config_tree, path_flavor, yajl_t_string);
+  if (val_flavor != NULL && YAJL_IS_STRING (val_flavor))
+    {
+      flavor = YAJL_GET_STRING (val_flavor);
+
+      // The SEV flavor will be used if the krun VM config indicates to use SEV
+      // within the "flavor" field.
+      sev_indicated |= strcmp (flavor, KRUN_FLAVOR_SEV) == 0;
+    }
+
+  // To maintain backward compatibility, also use the SEV flavor if the
+  // KRUN_SEV_FILE was found.
+  sev_indicated |= access (KRUN_SEV_FILE, F_OK) == 0;
+
+  if (sev_indicated)
+    {
+      if (kconf->handle_sev == NULL)
+        error (EXIT_FAILURE, 0, "the container requires libkrun-sev but it's not available");
+
+      kconf->handle = kconf->handle_sev;
+      kconf->ctx_id = kconf->ctx_id_sev;
+      kconf->sev = true;
+    }
+  else
+    {
+      if (kconf->handle == NULL)
+        error (EXIT_FAILURE, 0, "the container requires libkrun but it's not available");
+
+      kconf->sev = false;
+    }
+
+  return 0;
+}
+
 static int
 libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname, char *const argv[])
 {
@@ -222,22 +268,12 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
   if (UNLIKELY (ret < 0))
     error (EXIT_FAILURE, -ret, "libkrun VM config exists, but unable to parse");
 
-  if (access (KRUN_SEV_FILE, F_OK) == 0)
-    {
-      if (kconf->handle_sev == NULL)
-        error (EXIT_FAILURE, 0, "the container requires libkrun-sev but it's not available");
-      handle = kconf->handle_sev;
-      ctx_id = kconf->ctx_id_sev;
-      kconf->sev = true;
-    }
-  else
-    {
-      if (kconf->handle == NULL)
-        error (EXIT_FAILURE, 0, "the container requires libkrun but it's not available");
-      handle = kconf->handle;
-      ctx_id = kconf->ctx_id;
-      kconf->sev = false;
-    }
+  ret = libkrun_configure_flavor (cookie, &config_tree, &err);
+  if (UNLIKELY (ret < 0))
+    error (EXIT_FAILURE, -ret, "unable to configure libkrun flavor");
+
+  handle = kconf->handle;
+  ctx_id = kconf->ctx_id;
 
   krun_set_log_level = dlsym (handle, "krun_set_log_level");
   krun_start_enter = dlsym (handle, "krun_start_enter");