/*
 * vat.c
 *
 * PURPOSE
 *	Virtual Allocation Table (VAT) management routines.
 *
 * DESCRIPTION
 *	This code uses a single page for a page directory, so the maximum size
 *	of a VAT is limited (examples: 4MB on i386, 16MB on Alpha). This is a
 *	reasonable limit.
 *
 *	Unused page directory entries are marked with a NULL, and unused block
 *	entries on a page are marked with 0xffffffff.
 *
 * HISTORY
 *	November 27, 1997 - Andrew E. Mileski
 *	Credit Rob Sims with the page table idea, and blame me for the code.
 */

#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/udf_fs_sb.h>

#define PGDIR_PAGES	(PAGE_SIZE / sizeof(__u32 *))
#define PG_MASK		(PAGE_MASK >> 2)
#define PG_SHIFT	(PAGE_SHIFT - 2)

/*
 * udf_vat_bmap
 *
 * PURPOSE
 *	By using the VAT, map a virtual block address to a real block address.
 *
 * HISTORY
 *	November 27, 1997 - Andrew E. Mileski
 *	Credit Rob Sims with the page table idea, and blame me for the code.
 */
extern __u32 *
udf_vat_bmap(struct super_block *sb, __u32 block)
{
	unsigned pgdir_levels, pg_index, pgdir_index;
	__u32 **pgdir;

	pgdir = UDF_SB(sb)->s_vat;

	/* If necessary, create a page directory */
	if (!pgdir) {
		pgdir = (__u32 **)get_free_page(GFP_KERNEL);
		if (!page_dir) {
			printk(KERN_ERR
				"udf: can't allocate VAT page directory\n");
			return NULL;
		}
		UDF_SB(sb)->s_vat = page_dir;
	}

	/* This is a lot faster than searching a list - thanks Rob! */
	pg_index = block & PG_MASK;	
	pgdir_index = block >> PG_SHIFT;

	/* Check for a huge VAT */
	while (pgdir_index >= PGDIR_PAGES) {
		printk(KERN_ERR "udf: huge VAT (%d)\n", block);
		return NULL;
	}

	/* If necessary, add a page to the VAT */
	if (!pgdir[pgdir_index]) {
		__u32 *new_page;
		new_page = (___u32 *)__get_free_page(GFP_KERNEL);
		if (!new_page) {
			printk(KERN_ERR "udf: can't allocate VAT page\n");
			return NULL;
		}
		memset(new_page, 0xff, PAGE_SIZE);
		pgdir[pgdir_index] = new_page;
	}

	return pgdir[pgdir_index] + pg_index;
}

/*
 * udf_vat_free
 *
 * PURPOSE
 *	Free all memory associated with the VAT.
 *
 * HISTORY
 *	November 27, 1997 - Andrew E. Mileski
 *	Credit Rob Sims with the page table idea, and blame me for the code.
 */
extern void
udf_vat_free(struct super_block *sb)
{
	unsigned page;
	__u32 **pgdir;

	pgdir = UDF_SB(sb)->s_vat;

	if (pgdir) {
		for (page = 0; page < PGDIR_PAGES; page++) {
			if (pgdir[page])
				free_page(page);
		}
		free_page(page_dir);
		UDF_SB(sb)->s_vat = NULL;
	}
}

#if 0
extern int
udf_vat_read(struct super_block *sb)
{
}

extern int
udf_vat_write(struct super_block *sb)
{
}
#endif