blk: blkmap: Add basic infrastructure

blkmaps are loosely modeled on Linux's device mapper subsystem. The
basic idea is that you can create virtual block devices whose blocks
can be backed by a plethora of sources that are user configurable.

This change just adds the basic infrastructure for creating and
removing blkmap devices. Subsequent changes will extend this to add
support for actual mappings.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/blkmap.h

@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2023 Addiva Elektronik
+ * Author: Tobias Waldekranz <tobias@waldekranz.com>
+ */
+
+#ifndef _BLKMAP_H
+#define _BLKMAP_H
+
+/**
+ * blkmap_from_label() - Find blkmap from label
+ *
+ * @label: Label of the requested blkmap
+ * Returns: A pointer to the blkmap on success, NULL on failure
+ */
+struct udevice *blkmap_from_label(const char *label);
+
+/**
+ * blkmap_create() - Create new blkmap
+ *
+ * @label: Label of the new blkmap
+ * @devp: If not NULL, updated with the address of the resulting device
+ * Returns: 0 on success, negative error code on failure
+ */
+int blkmap_create(const char *label, struct udevice **devp);
+
+/**
+ * blkmap_destroy() - Destroy blkmap
+ *
+ * @dev: The blkmap to be destroyed
+ * Returns: 0 on success, negative error code on failure
+ */
+int blkmap_destroy(struct udevice *dev);
+
+#endif	/* _BLKMAP_H */