static void vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s,
                              Error **errp)
{
    int ret;
    VHDXHeader *header1;
    VHDXHeader *header2;
    bool h1_valid = false;
    bool h2_valid = false;
    uint64_t h1_seq = 0;
    uint64_t h2_seq = 0;
    uint8_t *buffer;

    /* header1 & header2 are freed in vhdx_close() */
    header1 = qemu_blockalign(bs, sizeof(VHDXHeader));
    header2 = qemu_blockalign(bs, sizeof(VHDXHeader));

    buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);

    s->headers[0] = header1;
    s->headers[1] = header2;

    /* We have to read the whole VHDX_HEADER_SIZE instead of
     * sizeof(VHDXHeader), because the checksum is over the whole
     * region */
    ret = bdrv_pread(bs->file, VHDX_HEADER1_OFFSET, buffer, VHDX_HEADER_SIZE);
    if (ret < 0) {
        goto fail;
    }
    /* copy over just the relevant portion that we need */
    memcpy(header1, buffer, sizeof(VHDXHeader));
    vhdx_header_le_import(header1);

    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
        !memcmp(&header1->signature, "head", 4)             &&
        header1->version == 1) {
        h1_seq = header1->sequence_number;
        h1_valid = true;
    }

    ret = bdrv_pread(bs->file, VHDX_HEADER2_OFFSET, buffer, VHDX_HEADER_SIZE);
    if (ret < 0) {
        goto fail;
    }
    /* copy over just the relevant portion that we need */
    memcpy(header2, buffer, sizeof(VHDXHeader));
    vhdx_header_le_import(header2);

    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
        !memcmp(&header2->signature, "head", 4)             &&
        header2->version == 1) {
        h2_seq = header2->sequence_number;
        h2_valid = true;
    }

    /* If there is only 1 valid header (or no valid headers), we
     * don't care what the sequence numbers are */
    if (h1_valid && !h2_valid) {
        s->curr_header = 0;
    } else if (!h1_valid && h2_valid) {
        s->curr_header = 1;
    } else if (!h1_valid && !h2_valid) {
        goto fail;
    } else {
        /* If both headers are valid, then we choose the active one by the
         * highest sequence number.  If the sequence numbers are equal, that is
         * invalid */
        if (h1_seq > h2_seq) {
            s->curr_header = 0;
        } else if (h2_seq > h1_seq) {
            s->curr_header = 1;
        } else {
            goto fail;
        }
    }

    vhdx_region_register(s, s->headers[s->curr_header]->log_offset,
                            s->headers[s->curr_header]->log_length);
    goto exit;

fail:
    error_setg_errno(errp, -ret, "No valid VHDX header found");
    qemu_vfree(header1);
    qemu_vfree(header2);
    s->headers[0] = NULL;
    s->headers[1] = NULL;
exit:
    qemu_vfree(buffer);
}
Unknown