ostree_kernel_args_contains for OstreeKernelArgs

Check if an argument is present in OstreeKernelArgs. This is a way to
make easier idempotent append and delete operations.
ostree_kernel_args_append_if_missing uses it to avoid inserting a
duplicate key.

Closes #2329

Signed-off-by: Rafael Garcia Ruiz <rafael.garcia@collabora.com>

src/libostree/libostree-devel.sym

@@ -20,6 +20,10 @@
    - uncomment the include in Makefile-libostree.am
 */
 
+LIBOSTREE_2022.7 {
+global:
+  ostree_kernel_args_contains;
+} LIBOSTREE_2022.5;
 
 /* Stub section for the stable release *after* this development one; don't
  * edit this other than to update the year.  This is just a copy/paste

src/libostree/ostree-kernel-args.c

@@ -820,12 +820,31 @@ void
 ostree_kernel_args_append_if_missing (OstreeKernelArgs  *kargs,
                                       const char *arg)
 {
-  g_autofree char *key = g_strdup (arg);
-  split_keyeq (key);
- 
   // Don't insert a duplicate key.
-  if (g_hash_table_contains (kargs->table, key))
+  if (ostree_kernel_args_contains (kargs, arg))
     return;
  
   ostree_kernel_args_append (kargs, arg);
 }
+
+/**
+ * ostree_kernel_args_contains:
+ * @kargs: a OstreeKernelArgs instance
+ * @arg: key or key/value pair to check
+ *
+ * Search for @arg which is in the form of key=value pair at the hash table kargs->table
+ * and returns true if finds it.
+ *
+ *Returns: %TRUE if @arg is contained in @kargs, %FALSE otherwise.
+ *
+ * Since: 2022.7
+ **/
+gboolean
+ostree_kernel_args_contains (OstreeKernelArgs  *kargs,
+                             const char *arg)
+{
+  g_autofree char *key = g_strdup (arg);
+  split_keyeq (key);
+
+  return g_hash_table_contains (kargs->table, key);
+}

src/libostree/ostree-kernel-args.h

@@ -134,4 +134,8 @@ _OSTREE_PUBLIC
 void ostree_kernel_args_append_if_missing (OstreeKernelArgs *kargs, 
                                            const char *arg);
 
+_OSTREE_PUBLIC
+gboolean ostree_kernel_args_contains (OstreeKernelArgs *kargs,
+                                      const char *arg);
+
 G_END_DECLS