Hi John, 2014-04-14 09:20, John W. Linville: > On Sat, Apr 12, 2014 at 08:05:22AM +0200, Thomas Monjalon wrote: > > 11/04/2014 20:08, Richardson, Bruce : > > > The ring PMD is probably best treated separately from the other PMDs as > > > it's not really a device poll-mode driver. Instead, it's a general > > > library that presents an API to make a ring, or set of rings, appear as > > > a poll-mode driver ethdev. The EAL command to have one created at > > > startup time was just an addon after-the-fact in case someone might > > > find it useful :-). However, it's primary purpose was to allow > > > applications to be written which could use physical NICs or rings > > > interchangeably. For example, an app with multiple stages in a > > > pipeline, where each stage just reads from an ethdev without caring if > > > it's actually reading from a port or from packets sent from another > > > lcore/function etc. Another example might be where an application > > > wishes to sometimes loop packets back to itself, in this case it uses > > > the C API to create an additional ring ethdev which it uses as output > > > port for any packets it wants looped back - no special handling needed, > > > everything is an ethdev to it on which it calls rx_burst or tx_burst. > > > It's also likely that in future we will develop other libraries which > > > wish to present their functionality via rx_burst/tx_burst functions > > > i.e. as an ethdev. > > > > I think you are describing a vdev and you want to be able to instantiate > > this vdev in your application code. Right? > > So why not make a generic API to be able to instantiate a vdev? > > Treating vdevs as something inherently different from the > hardware-backed PMDs continues to be the wrong approach. > > Ordinarily the whole point of having an abstraction that looks like > a hardware device is so that applications can use either hardware > or that abstraction without having to know the difference. Forcing > applications to be vdev-aware defeats the whole purpose of wrapping > those constructs inside a PMD in the first place.
I think there is a misunderstanding here. >From the user's point of view, it must be possible to create some virtual devices instead of using real ones. That's --vdev option. Then the device is handled as any other one thanks to its PMD. >From the application's point of view, all devices must be handled with the same API (ethdev). But sometimes, application wants to force creation of virtual devices like pmd_ring. So we need an API for this creation part. Then the device is still handled with the generic ethdev API. Do you still see any problem with this approach? Hope it's clear. -- Thomas
