Re: [dpdk-dev] [PATCH 2/3] net/vdpa_virtio_pci: introduce vdpa sample driver

["Wang, Xiao W" <xiao.w.wang@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Tuesday, February 6, 2018 10:24 PM
> To: Wang, Xiao W <xiao.w.wang@intel.com>; dev@dpdk.org
> Cc: Tan, Jianfeng <jianfeng.tan@intel.com>; Bie, Tiwei <tiwei.bie@intel.com>;
> yliu@fridaylinux.org; Liang, Cunming <cunming.liang@intel.com>; Daly, Dan
> <dan.daly@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>
> Subject: Re: [PATCH 2/3] net/vdpa_virtio_pci: introduce vdpa sample driver
> 
> Hi Xiao,
> 
> On 02/04/2018 03:55 PM, Xiao Wang wrote:
> > This driver is a reference sample of making vDPA device driver based
> > on vhost lib, this driver uses a standard virtio-net PCI device as
> > vDPA device, it can serve as a backend for a virtio-net pci device
> > in nested VM.
> >
> > The key driver ops implemented are:
> >
> > * vdpa_virtio_eng_init
> > Mapping virtio pci device with VFIO into userspace, and read device
> > capability and intialize internal data.
> >
> > * vdpa_virtio_eng_uninit
> > Release the mapped device.
> >
> > * vdpa_virtio_info_query
> > Device capability reporting, e.g. queue number, features.
> >
> > * vdpa_virtio_dev_config
> > With the guest virtio information provideed by vhost lib, this
> > function configures device and IOMMU to set up vhost datapath,
> > which includes: Rx/Tx vring, VFIO interrupt, kick relay.
> >
> > * vdpa_virtio_dev_close
> > Unset the stuff that are configured previously by dev_conf.
> >
> > This driver requires the virtio device supports VIRTIO_F_IOMMU_PLATFORM
> > , because the buffer address written in desc is IOVA.
> >
> > Because vDPA driver needs to set up MSI-X vector to interrupt the guest,
> > only vfio-pci is supported currently.
> >
> > Signed-off-by: Xiao Wang<xiao.w.wang@intel.com>
> > ---
> >   config/common_base                                 |    6 +
> >   config/common_linuxapp                             |    1 +
> >   drivers/net/Makefile                               |    1 +
> >   drivers/net/vdpa_virtio_pci/Makefile               |   31 +
> >   .../net/vdpa_virtio_pci/rte_eth_vdpa_virtio_pci.c  | 1527
> ++++++++++++++++++++
> >   .../rte_vdpa_virtio_pci_version.map                |    4 +
> >   mk/rte.app.mk                                      |    1 +
> >   7 files changed, 1571 insertions(+)
> >   create mode 100644 drivers/net/vdpa_virtio_pci/Makefile
> >   create mode 100644 drivers/net/vdpa_virtio_pci/rte_eth_vdpa_virtio_pci.c
> >   create mode 100644
> drivers/net/vdpa_virtio_pci/rte_vdpa_virtio_pci_version.map
> 
> Is there a specific constraint that makes you expose PCI functions and
> duplicate a lot of vfio code into the driver?

The existing vfio code doesn't fit VDPA well, this vDPA driver needs to program IOMMU for a vDPA device with a VM's memory table.
While the eal/vfio uses a struct vfio_cfg to takes all regular devices and add them to a single vfio_container, and program IOMMU with DPDK process's memory table.

This driver doing PCI VFIO initialization itself can avoid affecting the global vfio_cfg structure.

> 
> Wouldn't it be better (if possible) to use RTE_PMD_REGISTER_PCI() & co.
> to benefit from all the existing infrastructure?

RTE_PMD_REGISTER_PCI() & co will make this driver as PCI driver (physical device), then this will conflict with the virtio_pmd.
So I make vDPA device driver as a vdev driver.

> 
> Maxime

Thanks for the comments,
Xiao