User pointer validity checks.

Added routines that check whether a user pointer is accessible by the kernel,
and if not ask the pager to map-in those pages. I haven't implemented yet the
bit that asks the pager for paging-in.

src/generic/space.c

@@ -0,0 +1,38 @@
+/*
+ * Addess space related routines.
+ *
+ * Copyright (C) 2008 Bahadir Balban
+ */
+#include INC_GLUE(memory.h)
+#include INC_GLUE(memlayout.h)
+#include INC_ARCH(exception.h)
+#include <l4/generic/space.h>
+#include <l4/api/space.h>
+#include <l4/api/errno.h>
+
+/*
+ * Checks whether the given user address is a valid userspace address.
+ * If so, whether it is currently mapped into its own address space.
+ * If its not mapped-in, it generates a page-in request to the thread's
+ * pager. If fault hasn't cleared, aborts.
+ */
+int check_access(unsigned long vaddr, unsigned long size, unsigned int flags)
+{
+	int err;
+
+	/* Do not allow ridiculously big sizes */
+	if (size >= USER_AREA_SIZE)
+		return -EINVAL;
+
+	/* Check if in user range, but this is more up to the pager to decide */
+	if (!(vaddr >= USER_AREA_START && vaddr < USER_AREA_END))
+		return -EINVAL;
+
+	/* If not mapped, ask pager whether this is possible */
+	if (!check_mapping(vaddr, size, flags))
+		if((err = pager_pagein_request(vaddr, size, flags)) < 0)
+			return err;
+
+	return 0;
+}
+