On 2019-11-04 22:55, Dr. David Alan Gilbert wrote:
* ge...@hostfission.com (ge...@hostfission.com) wrote:
On 2019-11-03 21:10, ge...@hostfission.com wrote:
> On 2019-11-01 02:52, Dr. David Alan Gilbert wrote:
> > * ge...@hostfission.com (ge...@hostfission.com) wrote:
> > >
> > >
> > > On 2019-11-01 01:52, Peter Maydell wrote:
> > > > On Thu, 31 Oct 2019 at 14:26, <ge...@hostfission.com> wrote:
> > > > > As the author of Looking Glass, I also have to consider the
> > > > > maintenance
> > > > > and the complexity of implementing the vhost protocol into the
> > > > > project.
> > > > > At this time a complete Porthole client can be implemented in 150
> > > > > lines
> > > > > of C without external dependencies, and most of that is boilerplate
> > > > > socket code. This IMO is a major factor in deciding to avoid
> > > > > vhost-user.
> > > >
> > > > This is essentially a proposal that we should make our project and
> > > > code more complicated so that your project and code can be simpler.
> > > > I hope you can see why this isn't necessarily an argument that will hold
> > > > very much weight for us :-)
> > >
> > > Certainly, I do which is why I am still going to see about using
> > > vhost,
> > > however, a device that uses vhost is likely more complex then
> > > the device
> > > as it stands right now and as such more maintenance would be
> > > involved on
> > > your end also. Or have I missed something in that vhost-user can
> > > be used
> > > directly as a device?
> >
> > The basic vhost-user stuff isn't actually that hard; if you aren't
> > actually shuffling commands over the queues you should find it pretty
> > simple - so I think your assumption about it being simpler if you
> > avoid
> > it might be wrong. It might be easier if you use it!
>
> I have been looking into this and I am yet to find some decent
> documentation or a simple device example I can use to understand how to
> create such a device. Do you know of any reading or examples I can
> obtain
> on how to get an initial do nothing device up and running?
>
> -Geoff
Scratch that, the design just solidified for me and I am now making
progress, however it seems that vhost-user can't do what we need here:
1) I dont see any way to recieve notification of socket disconnection,
in
our use case the client app needs to be able to be (re)connected
dynamically. It might be possible to get this event by registering it
on
the chardev manually but this seems like it would be a kludge.
My understanding was that someone added support for reconnection of
vhost-user; I'm not sure of the detail - cc'ing in Maxime and
Marc-Andre.
2) I don't see any method of notifying the vhost-user client of the
removal of a shared memory mapping. Again, these may not be
persistently
mapped in the guest as we have no control over the buffer allocation,
and
as such, we need a method to notify the client that the mapping has
become
invalid.
3) VHOST_USER_SET_MEM_TABLE is a one time request, again this breaks
our
usage as we need to change this dynamically at runtime.
I've seen (3) being sent multiple times (It's messy but it happens); so
I think that fixes (2) as well for you.
Yes, but it's ignored.
/*
* For non-vring specific requests, like VHOST_USER_SET_MEM_TABLE,
* we just need send it once in the first time. For later such
* request, we just ignore it.
*/
if (vhost_user_one_time_request(msg->hdr.request) && dev->vq_index
!= 0) {
msg->hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK;
return 0;
}
Dave
Unless there are viable solutions to these problems there is no way
that
vhost-user can be used for this kind of a device.
-Geoff
>
> >
> > Dave
> >
> > > >
> > > > thanks
> > > > -- PMM
> > --
> > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
