From: John Levon <levon@movementarian.org>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: benjamin.walker@intel.com,
Elena Ufimtseva <elena.ufimtseva@oracle.com>,
Swapnil Ingle <swapnil.ingle@nutanix.com>,
John G Johnson <john.g.johnson@oracle.com>,
Jason Wang <jasowang@redhat.com>,
qemu-devel@nongnu.org,
Christophe de Dinechin <cdupontd@redhat.com>,
Kirti Wankhede <kwankhede@nvidia.com>,
Gerd Hoffmann <kraxel@redhat.com>,
Raphael Norwitz <raphael.norwitz@nutanix.com>,
jag.raman@oracle.com, james.r.harris@intel.com,
John Levon <john.levon@nutanix.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
Kanth.Ghatraju@oracle.com, Felipe Franciosi <felipe@nutanix.com>,
marcandre.lureau@redhat.com, Yan Zhao <yan.y.zhao@intel.com>,
konrad.wilk@oracle.com, yuvalkashtan@gmail.com,
dgilbert@redhat.com, eafanasova@gmail.com, ismael@linux.com,
Paolo Bonzini <pbonzini@redhat.com>,
changpeng.liu@intel.com, tomassetti.andrea@gmail.com,
mpiszczek@ddn.com, Cornelia Huck <cohuck@redhat.com>,
alex.williamson@redhat.com, tina.zhang@intel.com,
xiuchun.lu@intel.com, Thanos Makatos <thanos.makatos@nutanix.com>
Subject: Re: [PATCH v8] introduce vfio-user protocol specification
Date: Tue, 11 May 2021 10:43:57 +0000 [thread overview]
Message-ID: <20210511104357.GA1964660@li1368-133.members.linode.com> (raw)
In-Reply-To: <YJpX8XT+WvXYkyMD@stefanha-x1.localdomain>
On Tue, May 11, 2021 at 11:09:53AM +0100, Stefan Hajnoczi wrote:
> > > > +* *sub-regions* is the array of Sub-Region IO FD info structures
> > > > +
> > > > +The reply message will additionally include at least one file descriptor in the
> > > > +ancillary data. Note that more than one sub-region may share the same file
> > > > +descriptor.
> > >
> > > How does this interact with the maximum number of file descriptors,
> > > max_fds? It is possible that there are more sub-regions than max_fds
> > > allows...
> >
> > I think this would just be a matter of the client advertising a reasonably large
> > enough size for max_msg_fds. Do we need to worry about this?
>
> vhost-user historically only supported passing 8 fds and it became a
> problem there.
>
> I can imagine devices having 10s to 100s of sub-regions (e.g. 64 queue
> doorbells). Probably not 1000s.
>
> If I was implementing a server I would check the negotiated max_fds and
> refuse to start the vfio-user connection if the device has been
> configured to require more sub-regions. Failing early and printing an
> error would allow users to troubleshoot the issue and re-configure the
> client/server.
>
> This seems okay but the spec doesn't mention it explicitly so I wanted
> to check what you had in mind.
Not for the spec, but I filed https://github.com/nutanix/libvfio-user/issues/489
to track this on the library side. Thanks.
> Fleshing out irqs sounds like a 1.0 milestone to me. It will definitely
> be necessary but for now this can be dropped.
I could be wrong, and probably am, but I believe we're basically fine for IRQs
right now, until we want to support servers on separate hosts where we'll
obviously have to re-introduce something like the VM_INTERRUPT message.
> > > > +VFIO_USER_DEVICE_RESET
> > > > +----------------------
> > >
> > > Any requirements for how long VFIO_USER_DEVICE_RESET takes to complete?
> > > In some cases a reset involves the server communicating with other
> > > systems or components and this can take an unbounded amount of time.
> > > Therefore this message could hang. For example, if a vfio-user NVMe
> > > device was accessing data on a hung NFS export and there were I/O
> > > requests in flight that need to be aborted.
> >
> > I'm not sure this is something we could put in the generic spec. Perhaps a
> > caveat?
>
> It's up to you whether you want to discuss this in the spec or let
> client implementors figure it out themselves. Any vfio-user message can
> take an unbounded amount of time and we could assume that readers will
> think of this.
I'm going to start an "implementation notes" section.
regards
john
next prev parent reply other threads:[~2021-05-11 11:25 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-14 11:41 [PATCH v8] introduce vfio-user protocol specification Thanos Makatos
2021-04-26 15:48 ` Stefan Hajnoczi
2021-04-27 12:02 ` Thanos Makatos
2021-04-27 15:01 ` Stefan Hajnoczi
2021-05-04 13:51 ` Stefan Hajnoczi
2021-05-04 14:31 ` John Levon
2021-05-05 15:51 ` Stefan Hajnoczi
2021-06-14 9:57 ` Thanos Makatos
2021-05-05 16:19 ` John Levon
2021-05-06 8:49 ` Stefan Hajnoczi
2021-05-07 16:10 ` Thanos Makatos
2021-06-14 10:07 ` Thanos Makatos
2021-05-10 16:57 ` Stefan Hajnoczi
2021-05-10 22:25 ` John Levon
2021-05-11 10:09 ` Stefan Hajnoczi
2021-05-11 10:43 ` John Levon [this message]
2021-05-11 15:40 ` Stefan Hajnoczi
2021-05-12 5:08 ` John Johnson
2021-05-19 21:08 ` Alex Williamson
2021-05-19 22:38 ` John Levon
2021-06-14 9:47 ` Thanos Makatos
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