Re: [Qemu-devel] [PATCH v2 for-4.0 2/7] vhost-user: Support providing shared memory to backend

[Yongji Xie]

On Tue, 18 Dec 2018 at 22:25, Michael S. Tsirkin <address@hidden> wrote:
>
> On Tue, Dec 18, 2018 at 05:59:57PM +0800, address@hidden wrote:
> > From: Xie Yongji <address@hidden>
> >
> > This patch introduces two new messages VHOST_USER_GET_SHM_SIZE
> > and VHOST_USER_SET_SHM_FD to support providing shared
> > memory to backend.
> >
> > Firstly, qemu uses VHOST_USER_GET_SHM_SIZE to get the
> > required size of shared memory from backend. Then, qemu
> > allocates memory and sends them back to backend through
> > VHOST_USER_SET_SHM_FD.
> >
> > Note that the shared memory should be used to record
> > inflight I/O by backend. Qemu will clear it when vm reset.
>
> An interesting design choice. Why not let the backend clear it
> on start?
>

The backend might restart when it has some inflight I/Os. In this case,
it should not clear the memory on start, right?

Thanks,
Yongji