base: add base/error.h for common error types

repos/base/include/base/error.h

@@ -0,0 +1,36 @@
+/*
+ * \brief  Error types
+ * \author Norman Feske
+ * \date   2025-03-05
+ */
+
+/*
+ * Copyright (C) 2025 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__BASE__ERROR_H_
+#define _INCLUDE__BASE__ERROR_H_
+
+namespace Genode {
+
+	/**
+	 * Common error returned by constrained allocators
+	 *
+	 * OUT_OF_RAM and OUT_OF_CAPS can in principle be resolved by upgrading
+	 * the resource budget of the allocator.
+	 *
+	 * DENIED expresses a situation where the allocator cannot satisfy the
+	 * allocation for unresolvable reasons. For example, the allocator may
+	 * have a hard limit of the number of allocations, or the allocation of
+	 * a large contiguous range is prevented by internal fragmentation, or
+	 * a requested alignment constraint cannot be met. In these cases, the
+	 * allocator reflects the condition to the caller to stay healthy and let
+	 * the caller fail gracefully or consciously panic at the caller side.
+	 */
+	enum class Alloc_error { OUT_OF_RAM, OUT_OF_CAPS, DENIED };
+}
+
+#endif /* _INCLUDE__BASE__ERROR_H_ */

repos/base/include/base/ram.h

@@ -15,6 +15,7 @@
 #define _INCLUDE__BASE__RAM_H_
 
 #include <util/allocation.h>
+#include <base/error.h>
 #include <base/capability.h>
 #include <base/quota_guard.h>
 #include <base/cache.h>
@@ -25,8 +26,7 @@ namespace Genode::Ram {
 	struct Dataspace : Genode::Dataspace { };
 
 	using Capability = Genode::Capability<Dataspace>;
-
-	enum class Error { OUT_OF_RAM, OUT_OF_CAPS, DENIED };
+	using Error      = Alloc_error;
 
 	struct Unmapped_allocator;