Re: [PATCH v11 18/26] block/rnbd: client: main functionality

[Jinpu Wang <jinpu.wang@cloud.ionos.com>]

On Sat, Mar 28, 2020 at 5:45 AM Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 2020-03-20 05:16, Jack Wang wrote:
> > +static void rnbd_clt_put_dev(struct rnbd_clt_dev *dev)
> > +{
> > +     might_sleep();
> > +
> > +     if (refcount_dec_and_test(&dev->refcount)) {
> > +             mutex_lock(&ida_lock);
> > +             ida_simple_remove(&index_ida, dev->clt_device_id);
> > +             mutex_unlock(&ida_lock);
> > +             kfree(dev->hw_queues);
> > +             rnbd_clt_put_sess(dev->sess);
> > +             mutex_destroy(&dev->lock);
> > +             kfree(dev);
> > +     }
> > +}
>
> Please use the coding style that is used elsewhere in the kernel, namely
> return early to keep the indentation level low.
Ok, will fix the coding style.
>
> > +enum {
> > +     RNBD_DELAY_10ms   = 10,
> > +     RNBD_DELAY_IFBUSY = -1,
> > +};
>
> How about removing the RNBD_DELAY_10ms constant and using 10/*ms*/ instead?
Sounds good.
>
> > +enum {
> > +     NO_WAIT = 0,
> > +     WAIT    = 1
> > +};
> > +
> > +static int send_usr_msg(struct rtrs_clt *rtrs, int dir,
> > +                     struct rnbd_iu *iu, struct kvec *vec, size_t nr,
> > +                     size_t len, struct scatterlist *sg, unsigned int sg_len,
> > +                     void (*conf)(struct work_struct *work),
> > +                     int *errno, bool wait)
>
> Are the NO_WAIT and WAIT perhaps values that are passed as the last
> argument to send_usr_msg()? If so, please use a proper enumeration type
> instead of 'bool'.
You're right, seems better to just remove the enum, "bool wait" is
self-explained.
>
> > +static int rnbd_client_getgeo(struct block_device *block_device,
> > +                            struct hd_geometry *geo)
> > +{
> > +     u64 size;
> > +     struct rnbd_clt_dev *dev;
> > +
> > +     dev = block_device->bd_disk->private_data;
> > +     size = dev->size * (dev->logical_block_size / SECTOR_SIZE);
> > +     geo->cylinders  = (size & ~0x3f) >> 6;  /* size/64 */
> > +     geo->heads      = 4;
> > +     geo->sectors    = 16;
> > +     geo->start      = 0;
> > +
> > +     return 0;
> > +}
>
> Is the "& ~0x3f" in the above function perhaps superfluous?
yes, will remove.
>
> > +static void rnbd_clt_dev_kick_mq_queue(struct rnbd_clt_dev *dev,
> > +                                     struct blk_mq_hw_ctx *hctx,
> > +                                     int delay)
> > +{
> > +     struct rnbd_queue *q = hctx->driver_data;
> > +
> > +     if (delay != RNBD_DELAY_IFBUSY)
> > +             blk_mq_delay_run_hw_queue(hctx, delay);
> > +     else if (unlikely(!rnbd_clt_dev_add_to_requeue(dev, q)))
> > +             /*
> > +              * If session is not busy we have to restart
> > +              * the queue ourselves.
> > +              */
> > +             blk_mq_delay_run_hw_queue(hctx, RNBD_DELAY_10ms);
> > +}
>
> I think the above code will be easier to read if RNBD_DELAY_10ms is
> changed into 10/*ms*/.
ok

>
> > +static blk_status_t rnbd_queue_rq(struct blk_mq_hw_ctx *hctx,
> > +                                const struct blk_mq_queue_data *bd)
> > +{
> > +     struct request *rq = bd->rq;
> > +     struct rnbd_clt_dev *dev = rq->rq_disk->private_data;
> > +     struct rnbd_iu *iu = blk_mq_rq_to_pdu(rq);
> > +     int err;
> > +
> > +     if (unlikely(dev->dev_state != DEV_STATE_MAPPED))
> > +             return BLK_STS_IOERR;
> > +
> > +     iu->permit = rnbd_get_permit(dev->sess, RTRS_IO_CON,
> > +                                   RTRS_PERMIT_NOWAIT);
> > +     if (unlikely(!iu->permit)) {
> > +             rnbd_clt_dev_kick_mq_queue(dev, hctx, RNBD_DELAY_IFBUSY);
> > +             return BLK_STS_RESOURCE;
> > +     }
> > +
> > +     blk_mq_start_request(rq);
> > +     err = rnbd_client_xfer_request(dev, rq, iu);
> > +     if (likely(err == 0))
> > +             return BLK_STS_OK;
> > +     if (unlikely(err == -EAGAIN || err == -ENOMEM)) {
> > +             rnbd_clt_dev_kick_mq_queue(dev, hctx, RNBD_DELAY_10ms);
> > +             rnbd_put_permit(dev->sess, iu->permit);
> > +             return BLK_STS_RESOURCE;
> > +     }
> > +
> > +     rnbd_put_permit(dev->sess, iu->permit);
> > +     return BLK_STS_IOERR;
> > +}
>
> Would it be possible to use the .get_budget / .put_budget callbacks for
> obtaining / releasing a "permit" object? I'm asking this because it was
> really tricky to get the .get_budget / .put_budget calls right in the
> block layer core. See also commit 0bca799b9280 ("blk-mq: order getting
> budget and driver tag") # v4.17.

Will check if we can use .get_budget/put_budget call back.
>
> Thanks,
>
> Bart.
Thanks Bart