spok_bdev_initialize
    Bdev
    BdevIoPoolSize
    BdevIoCacheSize

    g_bdev_mgr.buf_io_pool
    g_bdev_mgr.buf_small_pool
    g_bdev_mgr.buf_large_pool

    spdk_io_device_register
        alloc & insert io_device to g_io_devices

    spok_bdev_modules_init
        g_bev_mgr.bdev_modules  —> module_init()

spdk_bdev_set_opts
    min_pool_size = bdev_io_cache_size & g_thread_count

spdk_bdev_io_set_buf