Re: [RFC v3 1/2] libnvdimm: Add flush callback for virtio pmem

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 13 Jul 2018 13:22:30 +0530
Pankaj Gupta <pagupta@redhat.com> wrote:

> This patch adds functionality to perform flush from guest to host
> over VIRTIO. We are registering a callback based on 'nd_region' type.
> As virtio_pmem driver requires this special flush interface, for rest
> of the region types we are registering existing flush function.
> Also report the error returned by virtio flush interface.

This patch doesn't apply against latest upstream. A few more comments
below.

> 
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
>  drivers/nvdimm/nd.h          |  1 +
>  drivers/nvdimm/pmem.c        |  4 ++--
>  drivers/nvdimm/region_devs.c | 24 ++++++++++++++++++------
>  include/linux/libnvdimm.h    |  5 ++++-
>  4 files changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h
> index 32e0364..1b62f79 100644
> --- a/drivers/nvdimm/nd.h
> +++ b/drivers/nvdimm/nd.h
> @@ -159,6 +159,7 @@ struct nd_region {
>  	struct badblocks bb;
>  	struct nd_interleave_set *nd_set;
>  	struct nd_percpu_lane __percpu *lane;
> +	int (*flush)(struct device *dev);
>  	struct nd_mapping mapping[0];
>  };
>  
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 9d71492..29fd2cd 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -180,7 +180,7 @@ static blk_qc_t pmem_make_request(struct request_queue *q, struct bio *bio)
>  	struct nd_region *nd_region = to_region(pmem);
>  
>  	if (bio->bi_opf & REQ_FLUSH)
> -		nvdimm_flush(nd_region);
> +		bio->bi_status = nvdimm_flush(nd_region);
>  
>  	do_acct = nd_iostat_start(bio, &start);
>  	bio_for_each_segment(bvec, bio, iter) {
> @@ -196,7 +196,7 @@ static blk_qc_t pmem_make_request(struct request_queue *q, struct bio *bio)
>  		nd_iostat_end(bio, start);
>  
>  	if (bio->bi_opf & REQ_FUA)
> -		nvdimm_flush(nd_region);
> +		bio->bi_status = nvdimm_flush(nd_region);
>  
>  	bio_endio(bio);
>  	return BLK_QC_T_NONE;
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index a612be6..124aae7 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -1025,6 +1025,7 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
>  	dev->of_node = ndr_desc->of_node;
>  	nd_region->ndr_size = resource_size(ndr_desc->res);
>  	nd_region->ndr_start = ndr_desc->res->start;
> +	nd_region->flush = ndr_desc->flush;
>  	nd_device_register(dev);
>  
>  	return nd_region;
> @@ -1065,13 +1066,10 @@ struct nd_region *nvdimm_volatile_region_create(struct nvdimm_bus *nvdimm_bus,
>  }
>  EXPORT_SYMBOL_GPL(nvdimm_volatile_region_create);
>  
> -/**
> - * nvdimm_flush - flush any posted write queues between the cpu and pmem media
> - * @nd_region: blk or interleaved pmem region
> - */
> -void nvdimm_flush(struct nd_region *nd_region)
> +void pmem_flush(struct device *dev)
>  {
> -	struct nd_region_data *ndrd = dev_get_drvdata(&nd_region->dev);
> +	struct nd_region_data *ndrd = dev_get_drvdata(dev);
> +	struct nd_region *nd_region = to_nd_region(dev);
>  	int i, idx;
>  
>  	/*
> @@ -1094,6 +1092,20 @@ void nvdimm_flush(struct nd_region *nd_region)
>  			writeq(1, ndrd_get_flush_wpq(ndrd, i, idx));
>  	wmb();
>  }
> +
> +/**
> + * nvdimm_flush - flush any posted write queues between the cpu and pmem media
> + * @nd_region: blk or interleaved pmem region
> + */
> +int nvdimm_flush(struct nd_region *nd_region)
> +{
> +	if (nd_region->flush)
> +		return(nd_region->flush(&nd_region->dev));
> +
> +	pmem_flush(&nd_region->dev);

IMHO, a better way of doing this would be to allow nvdimm_flush() to
be overridden. That is, in nd_region_create() you set nd_region->flush
to the original nvdimm_flush() if ndr_desc->flush is NULL. And then
always call nd_region->flush() where nvdimm_flush() is called today.

> +
> +	return 0;
> +}
>  EXPORT_SYMBOL_GPL(nvdimm_flush);
>  
>  /**
> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
> index 097072c..33b617f 100644
> --- a/include/linux/libnvdimm.h
> +++ b/include/linux/libnvdimm.h
> @@ -126,6 +126,7 @@ struct nd_region_desc {
>  	int numa_node;
>  	unsigned long flags;
>  	struct device_node *of_node;
> +	int (*flush)(struct device *dev);
>  };
>  
>  struct device;
> @@ -201,7 +202,9 @@ unsigned long nd_blk_memremap_flags(struct nd_blk_region *ndbr);
>  unsigned int nd_region_acquire_lane(struct nd_region *nd_region);
>  void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane);
>  u64 nd_fletcher64(void *addr, size_t len, bool le);
> -void nvdimm_flush(struct nd_region *nd_region);
> +int nvdimm_flush(struct nd_region *nd_region);
> +void pmem_set_flush(struct nd_region *nd_region, void (*flush)
> +					(struct device *));

It seems pmem_set_flush() doesn't exist.

>  int nvdimm_has_flush(struct nd_region *nd_region);
>  int nvdimm_has_cache(struct nd_region *nd_region);
>