Linux Virtualization - May 2019 - [PATCH v8 2/6] virtio-pmem: Add virtio pmem driver

>>
>>> +	}
>>> +
>>> +	/* 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.
>  
>>
>>> +
>>> +	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 ;) )

...
>> 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 :)
>>
>>> +	nvdimm_bus_unregister(nvdimm_bus);
>>> +	vdev->config->del_vqs(vdev);
>>> +	vdev->config->reset(vdev);
>>> +}
>>> +
-- 

Thanks,

David / dhildenb

> 
> >>
> >>> +	}
> >>> +
> >>> +	/* 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
>

>>
>> 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.
Hehe, thanks, that was the part that I was missing!

-- 

Thanks,

David / dhildenb