From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Subject: Re: [PATCH v3 4/9] vhost: Add API to get MTU value
Date: Fri, 17 Mar 2017 13:32:51 +0800
Message-ID: <20170317053251.GA18844@yliu-dev.sh.intel.com>
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To: Maxime Coquelin <maxime.coquelin@redhat.com>
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On Thu, Mar 16, 2017 at 12:37:23PM +0100, Maxime Coquelin wrote:
> 
> 
> On 03/16/2017 09:00 AM, Yuanhan Liu wrote:
> >On Sun, Mar 12, 2017 at 05:34:01PM +0100, Maxime Coquelin wrote:
> >>This patch implements the function for the application to
> >>get the MTU value.
> >
> >I'm thinking the other way. As we are making vhost being generic, it
> >doesn't make too much sense now to store a net specific value at vhost
> >layer. I'm thinking we may could introduce a vhost-user request handler,
> >something like:
> >
> >	rte_vhost_driver_register_msg_handler(socket, handler);
> 
> That's a good point.
> 
> >All vhost-user message then will goto the driver's sepcific handler.
> >if it's handlered, do nothing in vhost lib. Otherwise, we handle it
> >in vhost lib.
> >
> >In this way, you could handle the mtu message inside vhost-pmd; thus,
> >there is no need to introduce one more (net specific) API.
> >
> >Thoughts?
> 
> I need to think more about it, but advantage of having a dedicated API
> is that in case the MTU value is not available, you can know from
> return code whether it is not yet available (-EAGAIN), or not supported
> (-ENOTSUP).
> 
> That could be managed with the callback tough, by calling the callback
> with a 0 mtu value if not supported, so that the application can be
> sure that if the callback hasn't been called, then it is just that it
> is not ready yet.
> 
> What do you think?

I don't think the application should even be aware of the callback.
Application should get the mtu from the ethdev layer, by the API
rte_eth_dev_get_mtu(). And such MTU request should be only handled
in vhost-pmd, to serve the rte_eth_dev_get_mtu() API.

	--yliu