[block] Add generic block device translator

Add a generic mechanism for providing block devices on top of a data
transfer interface (such as HTTP).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/blocktrans.h

@@ -0,0 +1,38 @@
+#ifndef _IPXE_BLOCKTRANS_H
+#define _IPXE_BLOCKTRANS_H
+
+/** @file
+ *
+ * Block device translator
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdint.h>
+#include <ipxe/refcnt.h>
+#include <ipxe/interface.h>
+#include <ipxe/xferbuf.h>
+#include <ipxe/uaccess.h>
+
+/** A block device translator */
+struct block_translator {
+	/** Reference count */
+	struct refcnt refcnt;
+	/** Block device interface */
+	struct interface block;
+	/** Data transfer interface */
+	struct interface xfer;
+
+	/** Data transfer buffer */
+	struct xfer_buffer xferbuf;
+	/** Data buffer */
+	userptr_t buffer;
+	/** Block size */
+	size_t blksize;
+};
+
+extern int block_translate ( struct interface *block,
+			     userptr_t buffer, size_t size );
+
+#endif /* _IPXE_BLOCKTRANS_H */

src/include/ipxe/errfile.h

@@ -69,6 +69,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_ansicol		       ( ERRFILE_CORE | 0x001d0000 )
 #define ERRFILE_ansicoldef	       ( ERRFILE_CORE | 0x001e0000 )
 #define ERRFILE_fault		       ( ERRFILE_CORE | 0x001f0000 )
+#define ERRFILE_blocktrans	       ( ERRFILE_CORE | 0x00200000 )
 
 #define ERRFILE_eisa		     ( ERRFILE_DRIVER | 0x00000000 )
 #define ERRFILE_isa		     ( ERRFILE_DRIVER | 0x00010000 )