static int guess_disk_lchs(BlockDriverState *bs, int *pcylinders, int *pheads, int *psectors) { uint8_t buf[BDRV_SECTOR_SIZE]; int i, heads, sectors, cylinders; struct partition *p; uint32_t nr_sects; uint64_t nb_sectors; bdrv_get_geometry(bs, &nb_sectors); /** * The function will be invoked during startup not only in sync I/O mode, * but also in async I/O mode. So the I/O throttling function has to * be disabled temporarily here, not permanently. */ if (bdrv_read_unthrottled(bs, 0, buf, 1) < 0) { return -1; } /* test msdos magic */ if (buf[510] != 0x55 || buf[511] != 0xaa) { return -1; } for (i = 0; i < 4; i++) { p = ((struct partition *)(buf + 0x1be)) + i; nr_sects = le32_to_cpu(p->nr_sects); if (nr_sects && p->end_head) { /* We make the assumption that the partition terminates on a cylinder boundary */ heads = p->end_head + 1; sectors = p->end_sector & 63; if (sectors == 0) { continue; } cylinders = nb_sectors / (heads * sectors); if (cylinders < 1 || cylinders > 16383) { continue; } *pheads = heads; *psectors = sectors; *pcylinders = cylinders; trace_hd_geometry_lchs_guess(bs, cylinders, heads, sectors); return 0; } } return -1; }