util-linux-ng-2.17.2/partx/dos.c

#include <stdio.h>

#include "blkdev.h"

#include "partx.h"
#include "dos.h"

static int
is_extended(int type) {
	return (type == 5 || type == 0xf || type == 0x85);
}

/* assemble badly aligned little endian integer */
static inline unsigned int
assemble4le(unsigned char *p) {
	return p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
}

static inline unsigned int
partition_start(struct partition *p) {
	return assemble4le(&(p->start_sect[0]));
}

static inline unsigned int
partition_size(struct partition *p) {
	return assemble4le(&(p->nr_sects[0]));
}

static int
read_extended_partition(int fd, struct partition *ep,
			struct slice *sp, int ns, int ssf)
{
	struct partition *p;
	unsigned long start, here;
	unsigned char *bp;
	int loopct = 0;
	int moretodo = 1;
	int i, n=0;

	here = start = partition_start(ep);;

	while (moretodo) {
		moretodo = 0;
		if (++loopct > 100)
			return n;

		bp = getblock(fd, here * ssf);	/* in 512 blocks */
		if (bp == NULL)
			return n;

		if (bp[510] != 0x55 || bp[511] != 0xaa)
			return n;

		p = (struct partition *) (bp + 0x1be);

		for (i=0; i<2; i++, p++) {
			if (partition_size(p) == 0 || is_extended(p->sys_type))
				continue;
			if (n < ns) {
				sp[n].start = (here + partition_start(p)) * ssf;
				sp[n].size = partition_size(p) * ssf;
				n++;
			} else {
				fprintf(stderr,
				    "dos_extd_partition: too many slices\n");
				return n;
			}
			loopct = 0;
		}

		p -= 2;
		for (i=0; i<2; i++, p++) {
			if (partition_size(p) != 0 &&
			    is_extended(p->sys_type)) {
				here = start + partition_start(p);
				moretodo = 1;
				break;
			}
		}
	}
	return n;
}

static int
is_gpt(int type) {
	return (type == 0xEE);
}

int
read_dos_pt(int fd, struct slice all, struct slice *sp, int ns) {
	struct partition *p;
	unsigned long offset = all.start;
	int i, n=0;
	unsigned char *bp;
	int ssf;

	bp = getblock(fd, offset);
	if (bp == NULL)
		return -1;

	if (bp[510] != 0x55 || bp[511] != 0xaa)
		return -1;

	/* msdos PT depends sector size... */
	if (blkdev_get_sector_size(fd, &ssf) != 0)
		ssf = DEFAULT_SECTOR_SIZE;

	/* ... but partx counts everything in 512-byte sectors */
	ssf /= 512;

	p = (struct partition *) (bp + 0x1be);
	for (i=0; i<4; i++) {
		if (is_gpt(p->sys_type))
			return 0;
		p++;
	}
	p = (struct partition *) (bp + 0x1be);
	for (i=0; i<4; i++) {
		/* always add, even if zero length */
		if (n < ns) {
			sp[n].start = partition_start(p) * ssf;
			sp[n].size = partition_size(p) * ssf;
			n++;
		} else {
			fprintf(stderr,
				"dos_partition: too many slices\n");
			break;
		}
		p++;
	}
	p = (struct partition *) (bp + 0x1be);
	for (i=0; i<4; i++) {
		if (is_extended(p->sys_type))
			n += read_extended_partition(fd, p, sp+n, ns-n, ssf);
		p++;
	}
	return n;
}