Re: [PATCH v8 2/6] virtio-pmem: Add virtio pmem driver

Pankaj Gupta
2019-05-14T09:47:30Z

>
> >>
> >>> + }
> >>> +
> >>> + /* When host has read buffer, this completes via host_ack */
> >>
> >> "A host repsonse results in "host_ack" getting called" ... ?
> >>
> >>> + wait_event(req->host_acked, req->done);
> >>> + err = req->ret;
> >>> +ret:
> >>> + kfree(req);
> >>> + return err;
> >>> +};
> >>> +
> >>> +/* The asynchronous flush callback function */
> >>> +int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> >>> +{
> >>> + int rc = 0;
> >>> +
> >>> + /* Create child bio for asynchronous flush and chain with
> >>> + * parent bio. Otherwise directly call nd_region flush.
> >>> + */
> >>> + if (bio && bio->bi_iter.bi_sector != -1) {
> >>> + struct bio *child = bio_alloc(GFP_ATOMIC, 0);
> >>> +
> >>> + if (!child)
> >>> + return -ENOMEM;
> >>> + bio_copy_dev(child, bio);
> >>> + child->bi_opf = REQ_PREFLUSH;
> >>> + child->bi_iter.bi_sector = -1;
> >>> + bio_chain(child, bio);
> >>> + submit_bio(child);
> >>
> >> return 0;
> >>
> >> Then, drop the "else" case and "int rc" and do directly
> >>
> >> if (virtio_pmem_flush(nd_region))
> >> return -EIO;
> >
> > and another 'return 0' here :)
> >
> > I don't like return from multiple places instead I prefer
> > single exit point from function.
>
> Makes this function more complicated than necessary. I agree when there
> are locks involved.

o.k. I will change as you suggest :)

>
> >
> >>
> >>> +
> >>> + return 0;
> >>> +};
> >>> +
> >>> +static int virtio_pmem_probe(struct virtio_device *vdev)
> >>> +{
> >>> + int err = 0;
> >>> + struct resource res;
> >>> + struct virtio_pmem *vpmem;
> >>> + struct nd_region_desc ndr_desc = {};
> >>> + int nid = dev_to_node(&vdev->dev);
> >>> + struct nd_region *nd_region;
> >>
> >> Nit: use reverse Christmas tree layout :)
> >
> > Done.
> >
> >>
> >>> +
> >>> + if (!vdev->config->get) {
> >>> + dev_err(&vdev->dev, "%s failure: config access disabled\n",
> >>> + __func__);
> >>> + return -EINVAL;
> >>> + }
> >>> +
> >>> + vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem), GFP_KERNEL);
> >>> + if (!vpmem) {
> >>> + err = -ENOMEM;
> >>> + goto out_err;
> >>> + }
> >>> +
> >>> + vpmem->vdev = vdev;
> >>> + vdev->priv = vpmem;
> >>> + err = init_vq(vpmem);
> >>> + if (err)
> >>> + goto out_err;
> >>> +
> >>> + virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> >>> + start, &vpmem->start);
> >>> + virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> >>> + size, &vpmem->size);
> >>> +
> >>> + res.start = vpmem->start;
> >>> + res.end = vpmem->start + vpmem->size-1;
> >>> + vpmem->nd_desc.provider_name = "virtio-pmem";
> >>> + vpmem->nd_desc.module = THIS_MODULE;
> >>> +
> >>> + vpmem->nvdimm_bus = nvdimm_bus_register(&vdev->dev,
> >>> + &vpmem->nd_desc);
> >>> + if (!vpmem->nvdimm_bus)
> >>> + goto out_vq;
> >>> +
> >>> + dev_set_drvdata(&vdev->dev, vpmem->nvdimm_bus);
> >>> +
> >>> + ndr_desc.res = &res;
> >>> + ndr_desc.numa_node = nid;
> >>> + ndr_desc.flush = async_pmem_flush;
> >>> + set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> >>> + set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
> >>> + nd_region = nvdimm_pmem_region_create(vpmem->nvdimm_bus, &ndr_desc);
> >>> +
> >>
> >> I'd drop this empty line.
> >
> > hmm.
> >
>
> The common pattern after allocating something, immediately check for it
> in the next line (like you do throughout this patch ;) )

Right. But rare times when I see space will beauty the code I tend to
add it. Maybe I should not :)

>
> ...
> >> You are not freeing "vdev->priv".
> >
> > vdev->priv is vpmem which is allocated using devm API.
>
> I'm confused. Looking at drivers/virtio/virtio_balloon.c:
>
> static void virtballoon_remove(struct virtio_device *vdev)
> {
> struct virtio_balloon *vb = vdev->priv;
>
> ...
>
> kfree(vb);
> }
>
> I think you should do the same here, vdev->priv is allocated in
> virtio_pmem_probe.
>
> But maybe I am missing something important here :)

Because virtio_balloon use "kzalloc" for allocation and needs to be freed.
But virtio pmem uses "devm_kzalloc" which takes care of automatically deleting
the device memory when associated device is detached.

Thanks,
Pankaj
>
> >>
> >>> + nvdimm_bus_unregister(nvdimm_bus);
> >>> + vdev->config->del_vqs(vdev);
> >>> + vdev->config->reset(vdev);
> >>> +}
> >>> +
>
> --
>
> Thanks,
>
> David / dhildenb
>