[PXEXT] Add FILE_API_CHECK API function

Add FILE_API_CHECK to the PXEXT API so the NBP can query the
availability and status of the API.

src/arch/i386/interface/pxe/pxe_call.c

 	PXENV_EXIT_t ( * file_read ) ( struct s_PXENV_FILE_READ * );
 	PXENV_EXIT_t ( * get_file_size ) ( struct s_PXENV_GET_FILE_SIZE * );
 	PXENV_EXIT_t ( * file_exec ) ( struct s_PXENV_FILE_EXEC * );
+	PXENV_EXIT_t ( * file_api_check ) ( struct s_PXENV_FILE_API_CHECK * );
 };
 
 /**
 		pxenv_call.file_exec = pxenv_file_exec;
 		param_len = sizeof ( pxenv_any.file_exec );
 		break;
+	case PXENV_FILE_API_CHECK:
+		pxenv_call.file_api_check = pxenv_file_api_check;
+		param_len = sizeof ( pxenv_any.file_api_check );
+		break;
 	default:
 		DBG ( "PXENV_UNKNOWN_%hx", opcode );
 		pxenv_call.unknown = pxenv_unknown;

src/include/pxe.h

 	struct s_PXENV_FILE_READ		file_read;
 	struct s_PXENV_GET_FILE_SIZE		get_file_size;
 	struct s_PXENV_FILE_EXEC		file_exec;
+	struct s_PXENV_FILE_API_CHECK		file_api_check;
 };
 
 typedef union u_PXENV_ANY PXENV_ANY_t;

src/include/pxe_api.h

 
 /** @} */ /* pxenv_file_exec */
 
+/** @defgroup pxenv_file_api_check PXENV_FILE_API_CHECK
+ *
+ * FILE API CHECK
+ *
+ * @{
+ */
+
+/** PXE API function code for pxenv_file_api_check() */
+#define PXENV_FILE_API_CHECK		0x00e6
+
+/** Parameter block for pxenv_file_api_check() */
+struct s_PXENV_FILE_API_CHECK {
+	PXENV_STATUS_t Status;		/**< PXE status code */
+	UINT16_t Size;			/**< Size of structure  */
+	UINT32_t Magic;			/**< Magic number */
+	UINT32_t Provider;		/**< Implementation identifier */
+	UINT32_t APIMask;		/**< Supported API functions */
+	UINT32_t Flags;			/**< Reserved for the future */
+} PACKED;
+
+typedef struct s_PXENV_FILE_API_CHECK PXENV_FILE_API_CHECK_t;
+
+extern PXENV_EXIT_t pxenv_file_api_check ( struct s_PXENV_FILE_API_CHECK *file_api_check );
+
+/** @} */ /* pxenv_file_api_check */
+
 /** @} */ /* pxe_file_api */
 
 /** @defgroup pxe_loader_api PXE Loader API

src/interface/pxe/pxe_file.c

 	file_exec->Status = PXENV_STATUS_SUCCESS;
 	return PXENV_EXIT_SUCCESS;
 }
+
+/**
+ * FILE API CHECK
+ *
+ * @v file_exec				Pointer to a struct s_PXENV_FILE_API_CHECK
+ * @v s_PXENV_FILE_API_CHECK::Magic     Inbound magic number (0x91d447b2)
+ * @ret #PXENV_EXIT_SUCCESS		Command was executed successfully
+ * @ret #PXENV_EXIT_FAILURE		Command was not executed successfully
+ * @ret s_PXENV_FILE_API_CHECK::Status	PXE status code
+ * @ret s_PXENV_FILE_API_CHECK::Magic	Outbound magic number (0xe9c17b20)
+ * @ret s_PXENV_FILE_API_CHECK::Provider "gPXE" (0x45585067)
+ * @ret s_PXENV_FILE_API_CHECK::APIMask API function bitmask
+ * @ret s_PXENV_FILE_API_CHECK::Flags	Reserved
+ *
+ */
+PXENV_EXIT_t pxenv_file_api_check ( struct s_PXENV_FILE_API_CHECK *file_api_check ) {
+	DBG ( "PXENV_FILE_API_CHECK" );
+
+	if ( file_api_check->Magic != 0x91d447b2 ) {
+		file_api_check->Status = PXENV_STATUS_BAD_FUNC;
+		return PXENV_EXIT_FAILURE;
+	} else if ( file_api_check->Size <
+		    sizeof(struct s_PXENV_FILE_API_CHECK) ) {
+		file_api_check->Status = PXENV_STATUS_OUT_OF_RESOURCES;
+		return PXENV_EXIT_FAILURE;
+	} else {
+		file_api_check->Status   = PXENV_STATUS_SUCCESS;
+		file_api_check->Size     = sizeof(struct s_PXENV_FILE_API_CHECK);
+		file_api_check->Magic    = 0xe9c17b20;
+		file_api_check->Provider = 0x45585067; /* "gPXE" */
+		file_api_check->APIMask  = 0x0000007f; /* Functions e0-e6 */
+		file_api_check->Flags    = 0;	       /* None defined */
+		return PXENV_EXIT_SUCCESS;
+	}
+}