/*
    libparted
    Copyright (C) 1998-2000, 2002, 2004, 2007, 2009-2014, 2019-2022 Free
    Software Foundation, Inc.

    This program 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.

    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <config.h>
#include "fat.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

/* Reads in the boot sector (superblock), and does a minimum of sanity
 * checking.  The goals are:
 *	- to detect fat file systems, even if they are damaged [i.e. not
 * return an error / throw an exception]
 *	- to fail detection if there's not enough information for
 * fat_boot_sector_probe_type() to work (or possibly crash on a divide-by-zero)
 */
int
fat_boot_sector_read (FatBootSector** bsp, const PedGeometry *geom)
{
	PED_ASSERT (bsp != NULL);
	PED_ASSERT (geom != NULL);

	if (!ped_geometry_read_alloc (geom, (void **)bsp, 0, 1))
		return 0;
	FatBootSector *bs = *bsp;

	if (PED_LE16_TO_CPU (bs->boot_sign) != 0xAA55) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("File system has an invalid signature for a FAT "
			  "file system."));
		return 0;
	}

	if (!bs->sector_size
            || PED_LE16_TO_CPU (bs->sector_size) % PED_SECTOR_SIZE_DEFAULT) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("File system has an invalid sector size for a FAT "
			  "file system."));
		return 0;
	}

	if (!bs->cluster_size) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("File system has an invalid cluster size for a FAT "
			  "file system."));
		return 0;
	}

	if (!bs->reserved) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("File system has an invalid number of reserved "
			  "sectors for a FAT file system."));
		return 0;
	}

	if (bs->fats < 1 || bs->fats > 4) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("File system has an invalid number of FATs."));
		return 0;
	}

	return 1;
}

/*
    Don't trust the FAT12, FAT16 or FAT32 label string.
 */
FatType _GL_ATTRIBUTE_PURE
fat_boot_sector_probe_type (const FatBootSector* bs, const PedGeometry* geom)
{
	PedSector	logical_sector_size;
	PedSector	first_cluster_sector;
	FatCluster	cluster_count;

	if (!PED_LE16_TO_CPU (bs->dir_entries))
		return FAT_TYPE_FAT32;

	logical_sector_size = PED_LE16_TO_CPU (bs->sector_size) / 512;

	first_cluster_sector
		= PED_LE16_TO_CPU (bs->reserved) * logical_sector_size
		  + 2 * PED_LE16_TO_CPU (bs->fat_length) * logical_sector_size
		  + PED_LE16_TO_CPU (bs->dir_entries)
			/ (512 / sizeof (FatDirEntry));
	cluster_count = (geom->length - first_cluster_sector)
			/ bs->cluster_size / logical_sector_size;
	if (cluster_count > MAX_FAT12_CLUSTERS)
		return FAT_TYPE_FAT16;
	else
		return FAT_TYPE_FAT12;
}

static int
_fat_table_entry_size (FatType fat_type)
{
	switch (fat_type) {
		case FAT_TYPE_FAT12:
		return 2;		/* FIXME: how? */

		case FAT_TYPE_FAT16:
		return 2;

		case FAT_TYPE_FAT32:
		return 4;
	}

	return 0;
}

/* Analyses the boot sector, and sticks appropriate numbers in
   fs->type_specific.

   Note: you need to subtract (2 * cluster_sectors) off cluster offset,
   because the first cluster is number 2.  (0 and 1 are not real clusters,
   and referencing them is a bug)
 */
int
fat_boot_sector_analyse (FatBootSector* bs, PedFileSystem* fs)
{
	FatSpecific*		fs_info = FAT_SPECIFIC (fs);
	int			fat_entry_size;

	PED_ASSERT (bs != NULL);

	fs_info->logical_sector_size = PED_LE16_TO_CPU (bs->sector_size) / 512;

	fs_info->sectors_per_track = PED_LE16_TO_CPU (bs->secs_track);
	fs_info->heads = PED_LE16_TO_CPU (bs->heads);
	if (fs_info->sectors_per_track < 1 || fs_info->sectors_per_track > 63
	    || fs_info->heads < 1 || fs_info->heads > 255) {
		PedCHSGeometry* bios_geom = &fs->geom->dev->bios_geom;
		int cyl_count = 0;

		if (fs_info->heads > 0 && fs_info->sectors_per_track > 0)
			cyl_count = fs->geom->dev->length / fs_info->heads
					/ fs_info->sectors_per_track;

		switch (ped_exception_throw (
			PED_EXCEPTION_ERROR,
			PED_EXCEPTION_IGNORE_CANCEL,
			_("The file system's CHS geometry is (%d, %d, %d), "
			  "which is invalid.  The partition table's CHS "
			  "geometry is (%d, %d, %d)."),
			 cyl_count, fs_info->heads, fs_info->sectors_per_track,
			 bios_geom->cylinders, bios_geom->heads,
			 bios_geom->sectors)) {

		case PED_EXCEPTION_CANCEL:
			return 0;

		case PED_EXCEPTION_IGNORE:
			break;

                default:
                        break;
		}
	}

	if (bs->sectors)
		fs_info->sector_count = PED_LE16_TO_CPU (bs->sectors)
						* fs_info->logical_sector_size;
	else
		fs_info->sector_count = PED_LE32_TO_CPU (bs->sector_count)
						* fs_info->logical_sector_size;

	fs_info->fat_table_count = bs->fats;
	fs_info->root_dir_entry_count = PED_LE16_TO_CPU (bs->dir_entries);
	fs_info->fat_offset = PED_LE16_TO_CPU (bs->reserved)
					* fs_info->logical_sector_size;
	fs_info->cluster_sectors = bs->cluster_size
				   * fs_info->logical_sector_size;
	fs_info->cluster_size = fs_info->cluster_sectors * 512;

	if (fs_info->logical_sector_size == 0) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("FAT boot sector says logical sector size is 0.  "
			  "This is weird. "));
		return 0;
	}
	if (fs_info->fat_table_count == 0) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("FAT boot sector says there are no FAT tables.  This "
			  "is weird. "));
		return 0;
	}
	if (fs_info->cluster_sectors == 0) {
		ped_exception_throw (PED_EXCEPTION_ERROR, PED_EXCEPTION_CANCEL,
			_("FAT boot sector says clusters are 0 sectors.  This "
			  "is weird. "));
		return 0;
	}

	fs_info->fat_type = fat_boot_sector_probe_type (bs, fs->geom);
	if (fs_info->fat_type == FAT_TYPE_FAT12) {
		ped_exception_throw (
			PED_EXCEPTION_NO_FEATURE,
			PED_EXCEPTION_CANCEL,
			_("File system is FAT12, which is unsupported."));
		return 0;
	}
	if (fs_info->fat_type == FAT_TYPE_FAT16) {
		fs_info->fat_sectors = PED_LE16_TO_CPU (bs->fat_length)
				       * fs_info->logical_sector_size;
		fs_info->serial_number
			= PED_LE32_TO_CPU (bs->u.fat16.serial_number);
		fs_info->root_cluster = 0;
		fs_info->root_dir_offset
			= fs_info->fat_offset
			  + fs_info->fat_sectors * fs_info->fat_table_count;
		fs_info->root_dir_sector_count
			= fs_info->root_dir_entry_count * sizeof (FatDirEntry)
			  / (512 * fs_info->logical_sector_size);
		fs_info->cluster_offset
			= fs_info->root_dir_offset
			  + fs_info->root_dir_sector_count;
	}
	if (fs_info->fat_type == FAT_TYPE_FAT32) {
		fs_info->fat_sectors = PED_LE32_TO_CPU (bs->u.fat32.fat_length)
					* fs_info->logical_sector_size;
		fs_info->serial_number
			= PED_LE32_TO_CPU (bs->u.fat32.serial_number);
		fs_info->info_sector_offset
		    = PED_LE16_TO_CPU (fs_info->boot_sector->u.fat32.info_sector)
			  * fs_info->logical_sector_size;
		fs_info->boot_sector_backup_offset
		  = PED_LE16_TO_CPU (fs_info->boot_sector->u.fat32.backup_sector)
			  * fs_info->logical_sector_size;
		fs_info->root_cluster
			= PED_LE32_TO_CPU (bs->u.fat32.root_dir_cluster);
		fs_info->root_dir_offset = 0;
		fs_info->root_dir_sector_count = 0;
		fs_info->cluster_offset
			= fs_info->fat_offset
			  + fs_info->fat_sectors * fs_info->fat_table_count;
	}

	fs_info->cluster_count
		= (fs_info->sector_count - fs_info->cluster_offset)
		  / fs_info->cluster_sectors;

	fat_entry_size = _fat_table_entry_size (fs_info->fat_type);
	if (fs_info->cluster_count + 2
			> fs_info->fat_sectors * 512 / fat_entry_size)
		fs_info->cluster_count
			= fs_info->fat_sectors * 512 / fat_entry_size - 2;

	fs_info->dir_entries_per_cluster
		= fs_info->cluster_size / sizeof (FatDirEntry);
	return 1;
}