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Date: Mon, 26 Sep 2016 11:19:42 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Wiles, Keith" <keith.wiles@intel.com>
Cc: Thomas Monjalon <thomas.monjalon@6wind.com>,
"Loftus, Ciara" <ciara.loftus@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
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Subject: Re: [dpdk-dev] [PATCH] net/vhost: Add function to retreive the
'vid' for a given port id
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On Fri, Sep 23, 2016 at 09:23:11PM +0000, Wiles, Keith wrote:
>
> Regards,
> Keith
>
> > On Sep 23, 2016, at 12:26 AM, Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> >
> > On Thu, Sep 22, 2016 at 06:43:55PM +0200, Thomas Monjalon wrote:
> >>>>>>>> There could be a similar need in other PMD.
> >>>>>>>> If we can get an opaque identifier of the device which is not the port id,
> >>>>>>>> we could call some specific functions of the driver not implemented in
> >>>>>>>> the generic ethdev API.
> >>>>>>>
> >>>>>>> That means you have to add/export the PMD API first. Isn't it against what
> >>>>>>> you are proposing -- "I think we should not add any API to the PMDs" ;)
> >>>>>>
> >>>>>> Yes you are totally right :)
> >>>>>> Except that in vhost case, we would not have any API in the PMD.
> >>>>>> But it would allow to have some specific API in other PMDs for the features
> >>>>>> which do not fit in a generic API.
> >>>>>
> >>>>> So, does that mean you are okay with this patch now? I mean, okay to introduce
> >>>>> a vhost PMD API?
> >>>>
> >>>> It means I would be in favor of introducing API in drivers for very specific
> >>>> features.
> >>>> In this case, I am not sure that retrieving an internal id is very specific.
> >>>
> >>> It's not, instead, it's very generic. The "internal id" is actually the
> >>> public interface to vhost-user application, like "fd" to file APIs.
> >>>
> >>> Instead of introducing a few specific wrappers/APIs, I'd prefer to
> >>> introduce a generic one to get the handle, and let the application to
> >>> call other vhost APIs.
> >>
> >> Yes it makes sense.
> >> I was thinking of introducing a function to get an internal id from ethdev,
> >> in order to use it with any driver or underlying library.
> >> But it would be an opaque pointer and you need an int.
> >> Note that we can cast an int into a pointer, so I am not sure what is best.
> >
> > Yes, that should work. But I just doubt what the "opaque pointer" could be
> > for other PMD drivers, and what the application could do with it. For a
> > typical nic PMD driver, I can think of nothing is valuable to export to
> > user applications.
> >
> > But maybe it's valuable to other virtual PMD drives as well, like the TAP
> > pmd from Keith?
>
> I do not see a need in the TAP PMD other then returning the FD for TUN/TAP device.
Yes, that's what I meant.
> Not sure what any application would need with the FD here, as it could cause some problems.
Me, neither.
> This feels like we are talking about a IOCTL like generic interface into the PMD. Then we can add new one types and reject types in the PMD that are not supported. Would this not be a better method for all future PMD APIs?
>
> Here is just a thought as to how to solve this problem without a PMD specific API. A number of current ethdev APIs could be removed to use the API below. The APIs would be removed from ethdev structure and have the current APIs use the API below. I know some are not happy with number of APIs in the ethdev structure.
>
> The API could be something like this:
> struct rte_tlv { /* Type/Length/Value like structure */
> uint16_t type; /* Type of command */
> uint16_t len; /* Length of data section on input and on output */
> uint16_t tlen; /* Total or max length of data buffer */
> uint8_t data[0];
> };
>
> int rte_eth_dev_ioctl(int pid, int qid, struct rte_tlv *tlv);
Looks like a very clean solution to me!
Thomas?
--yliu
>
> >
> > If so, we may go that way.
> >
> > Another thought is that, it may be a bit weird to me to introduce an API
> > to get an opaque pointer. I mean, it's a bit hard to document it, because
> > it has different meaning for different drivers. Should we list all of
> > them then?
> >
> > --yliu