vm: add vm-object to represent non-contiguous physical memory allocations

vm-object can be used to demand-allocate non-contiguous physical memory, and
will provide an api for userspace programs to do the same. unless a vm-object
is created in-place (i.e. to represent a specific area of physical memory),
its memory pages are only allocated when the object is mapped AND someone
attempts to access the memory.

include/mango/vm-object.h

@@ -0,0 +1,68 @@
+#ifndef MANGO_VM_OBJECT_H_
+#define MANGO_VM_OBJECT_H_
+
+#include <mango/locks.h>
+#include <mango/object.h>
+
+#define VM_OBJECT_NAME_MAX 64
+
+enum vm_object_flags {
+	/* the memory behind this vm-object wasn't allocated by us, and
+	 * therefore shouldn't be freed by us */
+	VMO_IN_PLACE = 0x01u,
+};
+
+struct vm_object {
+	struct object vo_base;
+
+	char vo_name[VM_OBJECT_NAME_MAX];
+	enum vm_object_flags vo_flags;
+
+	/* queue of struct vm_region_mapping */
+	struct queue vo_mappings;
+
+	/* memory protection flags. mappings of this vm_object can only use
+	 * a subset of the flags set in this mask. */
+	enum vm_prot vo_prot;
+
+	/* btree of vm_pages that have been allocated to this vm_object.
+	 * vm_page->p_vmo_offset and the size of each page is the bst key. */
+	struct btree vo_pages;
+	/* total length of the vm_object in bytes. */
+	size_t vo_size;
+};
+
+extern kern_status_t vm_object_type_init(void);
+
+/* create a vm_object with the specified length in bytes and protection flags.
+ * the length will be automatically rounded up to the nearest vm_object page
+ * order size. the actual page frames themselves won't be allocated until
+ * they are mapped and accessed. */
+extern struct vm_object *vm_object_create(
+	const char *name,
+	size_t len,
+	enum vm_prot prot);
+
+/* create a vm_object that represents the specified range of physical memory.
+ * the length will be automatically rounded up to the nearest vm_object page
+ * order size.
+ * NOTE this function assumes that the physical memory has already been
+ * reserved, and is not in use by any other kernel component. */
+extern struct vm_object *vm_object_create_in_place(
+	const char *name,
+	phys_addr_t base,
+	size_t len,
+	enum vm_prot prot);
+
+extern struct vm_page *vm_object_get_page(
+	const struct vm_object *vo,
+	off_t offset);
+
+extern struct vm_page *vm_object_alloc_page(
+	struct vm_object *vo,
+	off_t offset,
+	enum vm_page_order size);
+
+DEFINE_OBJECT_LOCK_FUNCTION(vm_object, vo_base)
+
+#endif