Re: [PATCH 07/24] DAX: virtio-fs: Add vhost-user slave commands for mapping

[Dr. David Alan Gilbert]

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> On Tue, Feb 09, 2021 at 07:02:07PM +0000, Dr. David Alan Gilbert (git) wrote:
> > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> > index d6085f7045..1deedd3407 100644
> > --- a/docs/interop/vhost-user.rst
> > +++ b/docs/interop/vhost-user.rst
> > @@ -1432,6 +1432,26 @@ Slave message types
> >  
> >    The state.num field is currently reserved and must be set to 0.
> >  
> > +``VHOST_USER_SLAVE_FS_MAP``
> > +  :id: 6
> > +  :equivalent ioctl: N/A
> > +  :slave payload: fd + n * (offset + address + len)
> 
> I'm not sure I understand this notation. '+' means field concatenation?
> Is 'fd' a field or does it indicate file descriptor passing?
> 
> I suggest using a struct name instead of informal notation so that the
> payload size and representation is clear.
> 
> The same applies for VHOST_USER_SLAVE_FS_UNMAP.
> 
> > +  :master payload: N/A
> > +
> > +  Requests that the QEMU mmap the given fd into the virtio-fs cache;
> 
> s/QEMU mmap the given fd/given fd be mmapped/
> 
> Please avoid mentioning QEMU specifically. Any VMM should be able to
> implement this spec.
> 
> The same applies for VHOST_USER_SLAVE_FS_UNMAP.

OK, I've changed this to:

+``VHOST_USER_SLAVE_FS_MAP``
+  :id: 6
+  :equivalent ioctl: N/A
+  :slave payload: ``struct VhostUserFSSlaveMsg``
+  :master payload: N/A
+
+  Requests that an fd, provided in the ancillary data, be mmapped
+  into the virtio-fs cache; multiple chunks can be mapped in one
+  command.
+  A reply is generated indicating whether mapping succeeded.
+
+``VHOST_USER_SLAVE_FS_UNMAP``
+  :id: 7
+  :equivalent ioctl: N/A
+  :slave payload: ``struct VhostUserFSSlaveMsg``
+  :master payload: N/A
+
+  Requests that the range in the virtio-fs cache is unmapped;
+  multiple chunks can be unmapped in one command.
+  A reply is generated indicating whether unmapping succeeded.
+

(Although it'll get a little more complicated as I rework for
Chirantan's comment)

Dave

> > +  multiple chunks can be mapped in one command.
> > +  A reply is generated indicating whether mapping succeeded.
> > +
> > +``VHOST_USER_SLAVE_FS_UNMAP``
> > +  :id: 7
> > +  :equivalent ioctl: N/A
> > +  :slave payload: n * (address + len)
> > +  :master payload: N/A
> > +
> > +  Requests that the QEMU un-mmap the given range in the virtio-fs cache;
> > +  multiple chunks can be unmapped in one command.
> > +  A reply is generated indicating whether unmapping succeeded.


-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK