Re: [RFC v2 4/4] vduse: Add new ioctl VDUSE_GET_RECONNECT_INFO

[Jason Wang <jasowang@redhat.com>]

On Thu, Sep 21, 2023 at 10:07 PM Cindy Lu <lulu@redhat.com> wrote:
>
> On Mon, Sep 18, 2023 at 4:49 PM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Tue, Sep 12, 2023 at 11:01 AM Cindy Lu <lulu@redhat.com> wrote:
> > >
> > > In VDUSE_GET_RECONNECT_INFO, the Userspace App can get the map size
> > > and The number of mapping memory pages from the kernel. The userspace
> > > App can use this information to map the pages.
> > >
> > > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > > ---
> > >  drivers/vdpa/vdpa_user/vduse_dev.c | 15 +++++++++++++++
> > >  include/uapi/linux/vduse.h         | 15 +++++++++++++++
> > >  2 files changed, 30 insertions(+)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index 680b23dbdde2..c99f99892b5c 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -1368,6 +1368,21 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > >                 ret = 0;
> > >                 break;
> > >         }
> > > +       case VDUSE_GET_RECONNECT_INFO: {
> > > +               struct vduse_reconnect_mmap_info info;
> > > +
> > > +               ret = -EFAULT;
> > > +               if (copy_from_user(&info, argp, sizeof(info)))
> > > +                       break;
> > > +
> > > +               info.size = PAGE_SIZE;
> > > +               info.max_index = dev->vq_num + 1;
> > > +
> > > +               if (copy_to_user(argp, &info, sizeof(info)))
> > > +                       break;
> > > +               ret = 0;
> > > +               break;
> > > +       }
> > >         default:
> > >                 ret = -ENOIOCTLCMD;
> > >                 break;
> > > diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> > > index d585425803fd..ce55e34f63d7 100644
> > > --- a/include/uapi/linux/vduse.h
> > > +++ b/include/uapi/linux/vduse.h
> > > @@ -356,4 +356,19 @@ struct vhost_reconnect_vring {
> > >         _Bool avail_wrap_counter;
> > >  };
> > >
> > > +/**
> > > + * struct vduse_reconnect_mmap_info
> > > + * @size: mapping memory size, always page_size here
> > > + * @max_index: the number of pages allocated in kernel,just
> > > + * use for check
> > > + */
> > > +
> > > +struct vduse_reconnect_mmap_info {
> > > +       __u32 size;
> > > +       __u32 max_index;
> > > +};
> >
> > One thing I didn't understand is that, aren't the things we used to
> > store connection info belong to uAPI? If not, how can we make sure the
> > connections work across different vendors/implementations. If yes,
> > where?
> >
> > Thanks
> >
> The process for this reconnecttion  is
> A.The first-time connection
> 1> The userland app checks if the device exists
> 2>  use the ioctl to create the vduse device
> 3> Mapping the kernel page to userland and save the
> App-version/features/other information to this page
> 4>  if the Userland app needs to exit, then the Userland app will only
> unmap the page and then exit
>
> B, the re-connection
> 1> the userland app finds the device is existing
> 2> Mapping the kernel page to userland
> 3> check if the information in shared memory is satisfied to
> reconnect,if ok then continue to reconnect
> 4> continue working
>
>  For now these information are all from userland,So here the page will
> be maintained by the userland App
> in the previous code we only saved the api-version by uAPI .  if  we
> need to support reconnection maybe we need to add 2 new uAPI for this,
> one of the uAPI is to save the reconnect  information and another is
> to get the information
>
> maybe something like
>
> struct vhost_reconnect_data {
> uint32_t version;
> uint64_t features;
> uint8_t status;
> struct virtio_net_config config;
> uint32_t nr_vrings;
> };

Probably, then we can make sure the re-connection works across
different vduse-daemon implementations.

>
> #define VDUSE_GET_RECONNECT_INFO _IOR (VDUSE_BASE, 0x1c, struct
> vhost_reconnect_data)
>
> #define VDUSE_SET_RECONNECT_INFO  _IOWR(VDUSE_BASE, 0x1d, struct
> vhost_reconnect_data)

Not sure I get this, but the idea is to map those pages to user space,
any reason we need this uAPI?

Thanks

>
> Thanks
> Cindy
>
>
>
>
> > > +
> > > +#define VDUSE_GET_RECONNECT_INFO \
> > > +       _IOWR(VDUSE_BASE, 0x1b, struct vduse_reconnect_mmap_info)
> > > +
> > >  #endif /* _UAPI_VDUSE_H_ */
> > > --
> > > 2.34.3
> > >
> >
>