DMA buffer in linux

static int fastrpc_dmabuf_alloc(struct fastrpc_user *fl, char __user *argp)
{
    struct fastrpc_alloc_dma_buf bp;
    DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
    struct fastrpc_buf *buf = NULL;
    int err;

    if (copy_from_user(&bp, argp, sizeof(bp)))
        return -EFAULT;

    err = fastrpc_buf_alloc(fl, fl->sctx->dev, bp.size, &buf);
    if (err)
        return err;
    exp_info.ops = &fastrpc_dma_buf_ops;
    exp_info.size = bp.size;
    exp_info.flags = O_RDWR;
    exp_info.priv = buf;
    buf->dmabuf = dma_buf_export(&exp_info);
    if (IS_ERR(buf->dmabuf)) {
        err = PTR_ERR(buf->dmabuf);
        fastrpc_buf_free(buf);
        return err;
    }

    bp.fd = dma_buf_fd(buf->dmabuf, O_ACCMODE);
    if (bp.fd < 0) {
        dma_buf_put(buf->dmabuf);
        return -EINVAL;
    }

    if (copy_to_user(argp, &bp, sizeof(bp))) {
        /*
         * The usercopy failed, but we can't do much about it, as
         * dma_buf_fd() already called fd_install() and made the
         * file descriptor accessible for the current process. It
         * might already be closed and dmabuf no longer valid when
         * we reach this point. Therefore "leak" the fd and rely on
         * the process exit path to do any required cleanup.
         */
        return -EFAULT;
    }

    return 0;

}