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Re: [Qemu-devel] [PATCH v9 2/7] virtio-pmem: Add virtio pmem driver


From: Pankaj Gupta
Subject: Re: [Qemu-devel] [PATCH v9 2/7] virtio-pmem: Add virtio pmem driver
Date: Thu, 16 May 2019 03:54:15 -0400 (EDT)

> >> +  vpmem->vdev = vdev;
> >> +  vdev->priv = vpmem;
> >> +  err = init_vq(vpmem);
> >> +  if (err) {
> >> +          dev_err(&vdev->dev, "failed to initialize virtio pmem vq's\n");
> >> +          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;
> > 
> > nit: " - 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) {
> >> +          dev_err(&vdev->dev, "failed to register device with 
> >> nvdimm_bus\n");
> >> +          err = -ENXIO;
> >> +          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);
> >> +  if (!nd_region) {
> >> +          dev_err(&vdev->dev, "failed to create nvdimm region\n");
> >> +          err = -ENXIO;
> >> +          goto out_nd;
> >> +  }
> >> +  nd_region->provider_data = dev_to_virtio(nd_region->dev.parent->parent);
> >> +  return 0;
> >> +out_nd:
> >> +  nvdimm_bus_unregister(vpmem->nvdimm_bus);
> >> +out_vq:
> >> +  vdev->config->del_vqs(vdev);
> >> +out_err:
> >> +  return err;
> >> +}
> >> +
> >> +static void virtio_pmem_remove(struct virtio_device *vdev)
> >> +{
> >> +  struct nvdimm_bus *nvdimm_bus = dev_get_drvdata(&vdev->dev);
> >> +
> >> +  nvdimm_bus_unregister(nvdimm_bus);
> >> +  vdev->config->del_vqs(vdev);
> >> +  vdev->config->reset(vdev);
> >> +}
> >> +
> >> +static struct virtio_driver virtio_pmem_driver = {
> >> +  .driver.name            = KBUILD_MODNAME,
> >> +  .driver.owner           = THIS_MODULE,
> >> +  .id_table               = id_table,
> >> +  .probe                  = virtio_pmem_probe,
> >> +  .remove                 = virtio_pmem_remove,
> >> +};
> >> +
> >> +module_virtio_driver(virtio_pmem_driver);
> >> +MODULE_DEVICE_TABLE(virtio, id_table);
> >> +MODULE_DESCRIPTION("Virtio pmem driver");
> >> +MODULE_LICENSE("GPL");
> >> diff --git a/drivers/nvdimm/virtio_pmem.h b/drivers/nvdimm/virtio_pmem.h
> >> new file mode 100644
> >> index 000000000000..ab1da877575d
> >> --- /dev/null
> >> +++ b/drivers/nvdimm/virtio_pmem.h
> >> @@ -0,0 +1,60 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +/*
> >> + * virtio_pmem.h: virtio pmem Driver
> >> + *
> >> + * Discovers persistent memory range information
> >> + * from host and provides a virtio based flushing
> >> + * interface.
> >> + **/
> >> +
> >> +#ifndef _LINUX_VIRTIO_PMEM_H
> >> +#define _LINUX_VIRTIO_PMEM_H
> >> +
> >> +#include <linux/virtio_ids.h>
> >> +#include <linux/module.h>
> >> +#include <linux/virtio_config.h>
> >> +#include <uapi/linux/virtio_pmem.h>
> >> +#include <linux/libnvdimm.h>
> >> +#include <linux/spinlock.h>
> >> +
> >> +struct virtio_pmem_request {
> >> +  /* Host return status corresponding to flush request */
> >> +  int ret;
> >> +
> >> +  /* command name*/
> >> +  char name[16];
> > 
> > So ... why are we sending string commands and expect native-endianess
> > integers and don't define a proper request/response structure + request
> > types in include/uapi/linux/virtio_pmem.h like
> > 
> > struct virtio_pmem_resp {
> >     __virtio32 ret;
> > }
> 
> FWIW, I wonder if we should even properly translate return values and
> define types like
> 
> VIRTIO_PMEM_RESP_TYPE_OK      0
> VIRTIO_PMEM_RESP_TYPE_EIO     1

Don't think these are required as only failure and success
return types easy to understand.

Thanks,
Pankaj
> 
> ..
> 
> > 
> > #define VIRTIO_PMEM_REQ_TYPE_FLUSH  1
> > struct virtio_pmem_req {
> >     __virtio16 type;
> > }
> > 
> > ... and this way we also define a proper endianess format for exchange
> > and keep it extensible
> > 
> > @MST, what's your take on this?
> > 
> > 
> 
> 
> --
> 
> Thanks,
> 
> David / dhildenb
> 



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