/* pc.c - Read PC style partition tables.  */
/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2002,2004,2005,2006,2007,2008,2009  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *(at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <r_types.h>
#include <grub/partition.h>
#include <grub/msdos_partition.h>
#include <grub/disk.h>
#include <grub/mm.h>
#include <grub/misc.h>
#include <grubfs.h>

struct grub_partition_map grub_msdos_partition_map;

static grub_err_t
pc_partition_map_iterate(grub_disk_t disk,
	int (*hook) (grub_disk_t disk,
		const grub_partition_t partition,
		void *closure),
	void *closure) {
	int i;
	struct grub_msdos_partition_entry *e;
	struct grub_partition p;
	struct grub_msdos_partition_mbr mbr;
	int labeln = 0;
	grub_disk_addr_t lastaddr;
	grub_disk_addr_t ext_offset;

	p.offset = 0;
	ext_offset = 0;
	p.number = -1;
	p.partmap = &grub_msdos_partition_map;

	/* Any value different than `p.offset' will satisfy the check during
	first loop.  */
	lastaddr = !p.offset;

	for (;;) {
		/* Read the MBR.  */
		if (grub_disk_read (disk, p.offset, 0, sizeof (mbr), &mbr)) {
			goto finish;
		}

		/* This is our loop-detection algorithm. It works the following way:
		It saves last position which was a power of two. Then it compares the
		saved value with a current one. This way it's guaranteed that the loop
		will be broken by at most third walk.
		 */
		if (labeln && lastaddr == p.offset) {
			return grub_error (GRUB_ERR_BAD_PART_TABLE, "loop detected");
		}

		labeln++;
		if ((labeln &(labeln - 1)) == 0) {
			lastaddr = p.offset;
		}

		/* Check if it is valid.  */
		if (mbr.signature != grub_cpu_to_le16 (GRUB_PC_PARTITION_SIGNATURE)) {
			fprintf (stderr, "msdos: no signature\n");
			return grub_error (GRUB_ERR_BAD_PART_TABLE, "no signature");
		}

		for (i = 0; i < 4; i++) {
			if (mbr.entries[i].flag & 0x7f) {
				fprintf (stderr, "msdos: bad boot flag\n");
				return grub_error (GRUB_ERR_BAD_PART_TABLE, "bad boot flag");
			}
		}

		/* Analyze DOS partitions.  */
		for (p.index = 0; p.index < 4; p.index++) {
			e = mbr.entries + p.index;

			p.start = p.offset + grub_le_to_cpu32 (e->start);
			p.len = grub_le_to_cpu32 (e->length);

			p.msdostype = e->type;
			grub_dprintf ("partition",
				"partition %d: flag 0x%x, type 0x%x, start 0x%" PFMT64x ", len 0x%" PFMT64x "\n",
				p.index,
				e->flag,
				e->type,
				(ut64)p.start,
				(ut64)p.len);

			/* If this is a GPT partition, this MBR is just a dummy.  */
			if (e->type == GRUB_PC_PARTITION_TYPE_GPT_DISK && p.index == 0) {
				return grub_error (GRUB_ERR_BAD_PART_TABLE, "dummy mbr");
			}

			/* If this partition is a normal one, call the hook.  */
			if (!grub_msdos_partition_is_empty (e->type) && !grub_msdos_partition_is_extended (e->type)) {
				p.number++;

				if (hook (disk, &p, closure)) {
					fprintf (stderr, "msdos: hook fail\n");
					return grub_errno;
				}
			} else if (p.number < 4) {
				/* If this partition is a logical one, shouldn't increase the
				partition number.  */
				p.number++;
			}
		}

		/* Find an extended partition.  */
		for (i = 0; i < 4; i++) {
			e = mbr.entries + i;

			if (grub_msdos_partition_is_extended (e->type)) {
				p.offset = ext_offset + grub_le_to_cpu32 (e->start);
				if (!ext_offset) {
					ext_offset = p.offset;
				}
				break;
			}
		}

		/* If no extended partition, the end.  */
		if (i == 4) {
			break;
		}
	}
finish:
	return grub_errno;
}

/* Partition map type.  */
struct grub_partition_map grub_msdos_partition_map = {
	.name = "msdos",
	.iterate = pc_partition_map_iterate,
};