linux-kernel - Re: [RFC v2 4/4] vduse: Add new ioctl VDUSE_GET_RECONNECT

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Message-ID: <CACLfguW3NS_4+YhqTtGqvQb70mVazGVfheryHx4aCBn+=Skf9w@mail.gmail.com>
Date:   Thu, 21 Sep 2023 22:01:46 +0800
From:   Cindy Lu <lulu@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, maxime.coquelin@...hat.com,
        xieyongji@...edance.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [RFC v2 4/4] vduse: Add new ioctl VDUSE_GET_RECONNECT_INFO

On Mon, Sep 18, 2023 at 4:49 PM Jason Wang <jasowang@...hat.com> wrote:
>
> On Tue, Sep 12, 2023 at 11:01 AM Cindy Lu <lulu@...hat.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@...hat.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;
};

#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)

Thanks
Cindy




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