From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bruce Richardson Subject: Re: [PATCH] net/vhost: Add function to retreive the 'vid' for a given port id Date: Mon, 26 Sep 2016 15:34:31 +0100 Message-ID: <20160926143430.GA20484@bricha3-MOBL3> References: <1473774463-26966-1-git-send-email-ciara.loftus@intel.com> <1895719.0W7iI9zMqJ@xps13> <20160926131835.GA21308@bricha3-MOBL3> <1649619.cdBSfnkg7V@xps13> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Wiles, Keith" , Yuanhan Liu , "Loftus, Ciara" , dev@dpdk.org To: Thomas Monjalon Return-path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id D7CCC2BB5 for ; Mon, 26 Sep 2016 16:35:57 +0200 (CEST) Content-Disposition: inline In-Reply-To: <1649619.cdBSfnkg7V@xps13> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Mon, Sep 26, 2016 at 04:26:27PM +0200, Thomas Monjalon wrote: > 2016-09-26 14:18, Bruce Richardson: > > On Mon, Sep 26, 2016 at 03:12:01PM +0200, Thomas Monjalon wrote: > > > 2016-09-23 21:23, Wiles, Keith: > > > > On Sep 23, 2016, at 12:26 AM, Yuanhan Liu 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. Not sure what any application would need with the FD here, as it could cause some problems. > > > > > > > > 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); > > > > > > Yes we are talking about having some specific functions per driver which > > > are not defined in the generic ethdev layer. > > > We need only one function in ethdev to give access to driver-specific API. > > > My idea is to convert the port id into an opaque handler. > > > Your idea is to use the port id in an ioctl like function. > > > > > > About the implementation, these are the 2 differences between my proposal > > > and yours: > > > - You use the well known port id, whereas I need another handler which is > > > understood by the driver. > > > - You need to build a message string which will be decoded by the driver. > > > I propose to directly offer some specific functions in the drivers which > > > are more convenient to use and easier for code review/debug. > > > > > > No conclusion here. I just want to make sure that we are on the same page, > > > and would like to have feedback from others. Thanks > > > > I personally don't like the idea of having a generic IOCTL in ethdev. If you > > want to have NIC-specific functions provided by a driver, that is fine, but > > any app using those is going to be limited to working only with that driver. > > > > In that case, since the driver in question is known, I don't see any reason > > to go through the ethdev layer. I think it would be much clearer to have the > > app instead include the driver's header file and call the driver function > > directly. The #include at the top of the file makes the dependency very clear, > > and having a function name instead of IOCTL with magic command numbers allows > > the action take by the function to be clearer too. > > So you are against an IOCTL API. Me too. > You agree that an application can be NIC-specific and include an header file > given by the driver to offer very specific features. Me too. > > My proposal was to convert the port id to an opaque pointer as handler of > these driver APIs. After an offline discussion, we agreed that it is not > necessary because drivers manage rte_eth_dev struct and port_id through > lib/librte_ether/rte_ethdev.h: extern struct rte_eth_dev rte_eth_devices[]; > +1. I agree with your proposal, and I also agree that no ethdev changes are necessary to support drivers having their own private functions.