ngx_chain_t *
ngx_writev_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
{
    ssize_t        n, sent;
    off_t          send, prev_send;
    ngx_uint_t     eintr;
    ngx_err_t      err;
    ngx_chain_t   *cl;
    ngx_event_t   *wev;
    ngx_iovec_t    vec;
    struct iovec   iovs[NGX_IOVS_PREALLOCATE];

    wev = c->write;

    if (!wev->ready) {
        return in;
    }

#if (NGX_HAVE_KQUEUE)

    if ((ngx_event_flags & NGX_USE_KQUEUE_EVENT) && wev->pending_eof) {
        (void) ngx_connection_error(c, wev->kq_errno,
                               "kevent() reported about an closed connection");
        wev->error = 1;
        return NGX_CHAIN_ERROR;
    }

#endif

    /* the maximum limit size is the maximum size_t value - the page size */

    if (limit == 0 || limit > (off_t) (NGX_MAX_SIZE_T_VALUE - ngx_pagesize)) {
        limit = NGX_MAX_SIZE_T_VALUE - ngx_pagesize;
    }

    send = 0;

    vec.iovs = iovs;
    vec.nalloc = NGX_IOVS_PREALLOCATE;

    for ( ;; ) {
        eintr = 0;
        prev_send = send;

        /* create the iovec and coalesce the neighbouring bufs */

        cl = ngx_output_chain_to_iovec(&vec, in, limit - send, c->log);

        if (cl == NGX_CHAIN_ERROR) {
            return NGX_CHAIN_ERROR;
        }

        if (cl && cl->buf->in_file) {
            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                          "file buf in writev "
                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
                          cl->buf->temporary,
                          cl->buf->recycled,
                          cl->buf->in_file,
                          cl->buf->start,
                          cl->buf->pos,
                          cl->buf->last,
                          cl->buf->file,
                          cl->buf->file_pos,
                          cl->buf->file_last);

            ngx_debug_point();

            return NGX_CHAIN_ERROR;
        }

        send += vec.size;

        n = writev(c->fd, vec.iovs, vec.count);

        if (n == -1) {
            err = ngx_errno;

            switch (err) {
            case NGX_EAGAIN:
                break;

            case NGX_EINTR:
                eintr = 1;
                break;

            default:
                wev->error = 1;
                (void) ngx_connection_error(c, err, "writev() failed");
                return NGX_CHAIN_ERROR;
            }

            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err,
                           "writev() not ready");
        }

        sent = n > 0 ? n : 0;

        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0, "writev: %z", sent);

        c->sent += sent;

        in = ngx_chain_update_sent(in, sent);

        if (eintr) {
            send = prev_send;
            continue;
        }

        if (send - prev_send != sent) {
            wev->ready = 0;
            return in;
        }

        if (send >= limit || in == NULL) {
            return in;
        }
    }
}