/*
 * This file implements the Page object.  A Page refers to a page of data in a
 * file or region of memory.  The offset tracks how far into the file the page
 * is, and the frame tracks where in physical memory the data is located.
 */

#include <nucleus/object.h>
#include <nucleus/memory.h>

/* Structure for a Page in a Cache */
struct Page {
	Object obj;
	off_t offset;
	page_t frame;
};

/* Information for find callback */
struct FindData {
	off_t offset;
	Page *result;
};

static void page_delete(Object *);

/* Page object type */
ObjectType pageType = {
	.name = "PAGE",
	.size = sizeof(Page),
	.delete = page_delete,
};

/* Destroy a Page object */
static void
page_delete(Object *obj)
{
	Page *page = (void *) obj;
	free_frame(PAGE_ADDR(page->frame));
}

/* Callback for finding a Page by offset */
static int
compare_page_offset(void *object, void *data)
{
	Page *page = object;
	struct FindData *find = data;
	if (page->offset == find->offset) {
		find->result = get(page);
		return 1;
	}
	return 0;
}

/* Create a new Page entry */
Page *
create_page(ObjectList *cache, page_t frame, off_t offset)
{
	Page *page = new(&pageType);
	page->frame = frame;
	page->offset = offset;
	add(cache, page);
	return page;
}

/* Find a Page by offset in a cache */
Page *
find_page(ObjectList *cache, off_t offset)
{
	struct FindData data = {
		.offset = offset,
		.result = NULL,
	};
	iterate(cache, compare_page_offset, &data);
	return data.result;
}

/* Get the virtual address for the mapping of a page */
void *
map_page(Page *page)
{
	/*
	 * Since this x86 kernel doesn't keep all physical memory mapped into
	 * the virtual address space, the page needs to be mapped into memory.
	 * If more virtual memory was available (e.g. x86_64) all of physical
	 * memory could be mapped to an offset, and this function would just
	 * return (page->frame + offset);
	 */
	set_page(0x7FF000, page->frame | PTE_PRESENT | PTE_WRITE);
	flush_tlb(0x7FF000);
	return (void *) 0x7FF000;
}