/*
* MS-DOS partition parsing code
*
* Copyright (C) 2009 Karel Zak <kzak@redhat.com>
*
* This file may be redistributed under the terms of the
* GNU Lesser General Public License.
*
* Inspired by fdisk, partx, Linux kernel and libparted.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include "partitions.h"
#include "dos.h"
#include "aix.h"
/* see superblocks/vfat.c */
extern int blkid_probe_is_vfat(blkid_probe pr);
static const struct dos_subtypes {
unsigned char type;
const struct blkid_idinfo *id;
} dos_nested[] = {
{ BLKID_FREEBSD_PARTITION, &bsd_pt_idinfo },
{ BLKID_NETBSD_PARTITION, &bsd_pt_idinfo },
{ BLKID_OPENBSD_PARTITION, &bsd_pt_idinfo },
{ BLKID_UNIXWARE_PARTITION, &unixware_pt_idinfo },
{ BLKID_SOLARIS_X86_PARTITION, &solaris_x86_pt_idinfo },
{ BLKID_MINIX_PARTITION, &minix_pt_idinfo }
};
static inline int is_extended(struct dos_partition *p)
{
return (p->sys_type == BLKID_DOS_EXTENDED_PARTITION ||
p->sys_type == BLKID_W95_EXTENDED_PARTITION ||
p->sys_type == BLKID_LINUX_EXTENDED_PARTITION);
}
static int parse_dos_extended(blkid_probe pr, blkid_parttable tab,
uint32_t ex_start, uint32_t ex_size, int ssf)
{
blkid_partlist ls = blkid_probe_get_partlist(pr);
uint32_t cur_start = ex_start, cur_size = ex_size;
unsigned char *data;
int ct_nodata = 0; /* count ext.partitions without data partitions */
int i;
while (1) {
struct dos_partition *p, *p0;
uint32_t start, size;
if (++ct_nodata > 100)
return 0;
data = blkid_probe_get_sector(pr, cur_start);
if (!data)
goto leave; /* malformed partition? */
if (!is_valid_mbr_signature(data))
goto leave;
p0 = (struct dos_partition *) (data + BLKID_MSDOS_PT_OFFSET);
/* Usually, the first entry is the real data partition,
* the 2nd entry is the next extended partition, or empty,
* and the 3rd and 4th entries are unused.
* However, DRDOS sometimes has the extended partition as
* the first entry (when the data partition is empty),
* and OS/2 seems to use all four entries.
* -- Linux kernel fs/partitions/dos.c
*
* See also http://en.wikipedia.org/wiki/Extended_boot_record
*/
/* Parse data partition */
for (p = p0, i = 0; i < 4; i++, p++) {
uint32_t abs_start;
blkid_partition par;
/* the start is relative to the parental ext.partition */
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
abs_start = cur_start + start; /* absolute start */
if (!size || is_extended(p))
continue;
if (i >= 2) {
/* extra checks to detect real data on
* 3rd and 4th entries */
if (start + size > cur_size)
continue;
if (abs_start < ex_start)
continue;
if (abs_start + size > ex_start + ex_size)
continue;
}
par = blkid_partlist_add_partition(ls, tab, abs_start, size);
if (!par)
goto err;
blkid_partition_set_type(par, p->sys_type);
blkid_partition_set_flags(par, p->boot_ind);
ct_nodata = 0;
}
/* The first nested ext.partition should be a link to the next
* logical partition. Everything other (recursive ext.partitions)
* is junk.
*/
for (p = p0, i = 0; i < 4; i++, p++) {
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
if (size && is_extended(p))
break;
}
if (i == 4)
goto leave;
cur_start = ex_start + start;
cur_size = size;
}
leave:
return 0;
err:
return -1;
}
static int probe_dos_pt(blkid_probe pr, const struct blkid_idmag *mag)
{
int i;
int ssf;
blkid_parttable tab = NULL;
blkid_partlist ls;
struct dos_partition *p0, *p;
unsigned char *data;
uint32_t start, size;
data = blkid_probe_get_sector(pr, 0);
if (!data)
goto nothing;
/* ignore disks with AIX magic number -- for more details see aix.c */
if (memcmp(data, BLKID_AIX_MAGIC_STRING, BLKID_AIX_MAGIC_STRLEN) == 0)
goto nothing;
/*
* Now that the 55aa signature is present, this is probably
* either the boot sector of a FAT filesystem or a DOS-type
* partition table.
*/
if (blkid_probe_is_vfat(pr)) {
DBG(DEBUG_LOWPROBE, printf("probably FAT -- ignore\n"));
goto nothing;
}
p0 = (struct dos_partition *) (data + BLKID_MSDOS_PT_OFFSET);
/*
* Reject PT where boot indicator is not 0 or 0x80.
*/
for (p = p0, i = 0; i < 4; i++, p++)
if (p->boot_ind != 0 && p->boot_ind != 0x80) {
DBG(DEBUG_LOWPROBE, printf("missing boot indicator -- ignore\n"));
goto nothing;
}
/*
* GPT uses valid MBR
*/
for (p = p0, i = 0; i < 4; i++, p++) {
if (p->sys_type == BLKID_GPT_PARTITION) {
DBG(DEBUG_LOWPROBE, printf("probably GPT -- ignore\n"));
goto nothing;
}
}
/*
* Well, all checks pass, it's MS-DOS partiton table
*/
if (blkid_partitions_need_typeonly(pr))
/* caller does not ask for details about partitions */
return 0;
ls = blkid_probe_get_partlist(pr);
/* sector size factor (the start and size are in the real sectors, but
* we need to convert all sizes to 512 logical sectors
*/
ssf = blkid_probe_get_sectorsize(pr) / 512;
/* allocate a new partition table */
tab = blkid_partlist_new_parttable(ls, "dos", BLKID_MSDOS_PT_OFFSET);
if (!tab)
goto err;
/* Parse primary partitions */
for (p = p0, i = 0; i < 4; i++, p++) {
blkid_partition par;
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
if (!size) {
/* Linux kernel ignores empty partitions, but partno for
* the empty primary partitions is not reused */
blkid_partlist_increment_partno(ls);
continue;
}
par = blkid_partlist_add_partition(ls, tab, start, size);
if (!par)
goto err;
blkid_partition_set_type(par, p->sys_type);
blkid_partition_set_flags(par, p->boot_ind);
}
/* Linux uses partition numbers greater than 4
* for all logical partition and all nested partition tables (bsd, ..)
*/
blkid_partlist_set_partno(ls, 5);
/* Parse logical partitions */
for (p = p0, i = 0; i < 4; i++, p++) {
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
if (!size)
continue;
if (is_extended(p) &&
parse_dos_extended(pr, tab, start, size, ssf) == -1)
goto err;
}
/* Parse subtypes (nested partitions) on large disks */
if (!blkid_probe_is_tiny(pr)) {
for (p = p0, i = 0; i < 4; i++, p++) {
int n;
if (!dos_partition_size(p) || is_extended(p))
continue;
for (n = 0; n < ARRAY_SIZE(dos_nested); n++) {
if (dos_nested[n].type != p->sys_type)
continue;
if (blkid_partitions_do_subprobe(pr,
blkid_partlist_get_partition(ls, i),
dos_nested[n].id) == -1)
goto err;
break;
}
}
}
return 0;
nothing:
return 1;
err:
return -1;
}
const struct blkid_idinfo dos_pt_idinfo =
{
.name = "dos",
.probefunc = probe_dos_pt,
.magics =
{
/* DOS master boot sector:
*
* 0 | Code Area
* 440 | Optional Disk signature
* 446 | Partition table
* 510 | 0x55
* 511 | 0xAA
*/
{ .magic = "\x55\xAA", .len = 2, .sboff = 510 },
{ NULL }
}
};
