static int curl_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
{
    BDRVCURLState *s = bs->opaque;
    CURLState *state = NULL;
    QemuOpts *opts;
    Error *local_err = NULL;
    const char *file;
    double d;
    static int inited = 0;
    if (flags & BDRV_O_RDWR) {
        error_setg(errp, "curl block device does not support writes");
        return -EROFS;
    }
    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
    qemu_opts_absorb_qdict(opts, options, &local_err);
    if (local_err) {
        error_propagate(errp, local_err);
        goto out_noclean;
    }
    s->readahead_size = qemu_opt_get_size(opts, CURL_BLOCK_OPT_READAHEAD,
                                          READ_AHEAD_DEFAULT);
    if ((s->readahead_size & 0x1ff) != 0) {
        error_setg(errp, "HTTP_READAHEAD_SIZE %zd is not a multiple of 512",
                   s->readahead_size);
        goto out_noclean;
    }
    file = qemu_opt_get(opts, CURL_BLOCK_OPT_URL);
    if (file == NULL) {
        error_setg(errp, "curl block driver requires an 'url' option");
        goto out_noclean;
    }
    if (!inited) {
        curl_global_init(CURL_GLOBAL_ALL);
        inited = 1;
    }
    DPRINTF("CURL: Opening %s\n", file);
    s->url = g_strdup(file);
    state = curl_init_state(s);
    if (!state)
        goto out_noclean;
    // Get file size
    s->accept_range = false;
    curl_easy_setopt(state->curl, CURLOPT_NOBODY, 1);
    curl_easy_setopt(state->curl, CURLOPT_HEADERFUNCTION,
                     curl_header_cb);
    curl_easy_setopt(state->curl, CURLOPT_HEADERDATA, s);
    if (curl_easy_perform(state->curl))
        goto out;
    curl_easy_getinfo(state->curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &d);
    if (d)
        s->len = (size_t)d;
    else if(!s->len)
        goto out;
    if ((!strncasecmp(s->url, "http://", strlen("http://"))
        || !strncasecmp(s->url, "https://", strlen("https://")))
        && !s->accept_range) {
        pstrcpy(state->errmsg, CURL_ERROR_SIZE,
                "Server does not support 'range' (byte ranges).");
        goto out;
    }
    DPRINTF("CURL: Size = %zd\n", s->len);
    curl_clean_state(state);
    curl_easy_cleanup(state->curl);
    state->curl = NULL;
    aio_timer_init(bdrv_get_aio_context(bs), &s->timer,
                   QEMU_CLOCK_REALTIME, SCALE_NS,
                   curl_multi_timeout_do, s);
    // Now we know the file exists and its size, so let's
    // initialize the multi interface!
    s->multi = curl_multi_init();
    curl_multi_setopt(s->multi, CURLMOPT_SOCKETFUNCTION, curl_sock_cb);
#ifdef NEED_CURL_TIMER_CALLBACK
    curl_multi_setopt(s->multi, CURLMOPT_TIMERDATA, s);
    curl_multi_setopt(s->multi, CURLMOPT_TIMERFUNCTION, curl_timer_cb);
#endif
    qemu_opts_del(opts);
    return 0;
out:
    error_setg(errp, "CURL: Error opening file: %s", state->errmsg);
    curl_easy_cleanup(state->curl);
    state->curl = NULL;
out_noclean:
    g_free(s->url);
    qemu_opts_del(opts);
    return -EINVAL;
}