Re: Re: Re: Re: [PATCH v2 06/11] transport-fabrics: introduce command set

[zhenwei pi <pizhenwei@bytedance.com>]

On 6/6/23 21:44, Stefan Hajnoczi wrote:
> On Tue, Jun 06, 2023 at 10:02:51AM +0800, zhenwei pi wrote:
> > On 6/6/23 00:30, Stefan Hajnoczi wrote:
> > [snip]
> > > > > > +
> > > > > > +The Target ID of 0xffff is reserved, then:
> > > > >
> > > > > Please move this after the fields have been shown and the purpose of the
> > > > > Target ID field has been explained.
> > > > >
> > > > > > +\begin{itemize}
> > > > > > +\item The Target ID of 0xffff MUST be specified as the Target ID in a Connect
> > > > > > +Command for the control queue.
> > > > > > +\item The target SHOULD allocate any available Target ID to the initiator,
> > > > > > +and return the allocated Target ID in the Completion.
> > > > > > +\item The returned Target ID MUST be specified as the Target ID, and the Queue ID
> > > > > > +MUST be specified in a Connect Command for the virtqueue.
> > > > > > +\end{itemize}
> > > > >
> > > > > What is the purpose of the Target ID? Is it to allow a server to provide
> > > > > access to multiple targets over the same connection?
> > > >
> > > > A target listens on a port, and provides access to 0 or more targets. An
> > > > initiator connect the specific target by TVQN of connect command.
> > > > An initiator could connect a single target, multiple initiators could
> > > > connect the same target(typically, shared disk/fs).
> > >
> > > Why is the target ID separate from the TVQN? If the Target ID is a
> > > separate parameter then users will have to learn additional
> > > syntax/command-line options to specify the TVQN + Target ID and that
> > > syntax may vary between software.
> >
> > The TVQN is the location of a target, for example:
> > virtio-tcp://192.168.1.110:8549/blk-dev/hdd-pool/238151a7-acd7-4621-bbdf-382ddbccb6a1
> >
> > A target can be shared by multi initiators, they accesses the target by the
> > same address(transport: tcp, ip: 192.168.1.110, port: 8549, TVQN:
> > blk-dev/hdd-pool/238151a7-acd7-4621-bbdf-382ddbccb6a1):
> >
> > Initiator_A launches Control Queue, issues connect command, gets the Target
> > ID of Target_A(typically, dynamically allocated by target), then virtqueues
> > connect to Target_A.
> >
> > Initiator_B launches Control Queue, issues connect command, gets the Target
> > ID of Target_B(typically, dynamically allocated by target), then virtqueues
> > connect to Target_B.
>
> In your example you say "A target can be shared by multi initiators" but
> then say "Target_A" and "Target_B", so the two initiators are not really
> communicating with the same target?

Yes, the two initiators are actually communicating with the same target 
of two Device Instances.

> Maybe instead of Target ID it should be called Device Instance ID? Then
> the "Target" is the server that listens on 192.168.1.110:8549 and the
> "Device Instance" is the VIRTIO device that the initiator is accessing
> through the Target. One Target may contain many Device Instances.
>
> I think that's clearer than calling boths Targets and Device Instances
> the same thing.
>
> Stefan

OK, this seems better! Fix this in next version.

--
zhenwei pi