Re: [dpdk-dev] [PATCH] pci: Add the class_id support in pci probe

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-01-29 11:21, Panu Matilainen:
> On 01/28/2016 11:38 PM, Thomas Monjalon wrote:
> > 2016-01-13 14:22, Panu Matilainen:
> >> On 01/13/2016 01:55 PM, Bruce Richardson wrote:
> >>> On Thu, Dec 31, 2015 at 09:12:14AM -0800, Stephen Hemminger wrote:
> >>>> On Tue, 29 Dec 2015 10:53:26 +0800
> >>>> Ziye Yang <ziye.yang@intel.com> wrote:
> >>>>
> >>>>> This patch is used to add the class_id support
> >>>>> for pci_probe since some devices need the class_info
> >>>>> (class_code, subclass_code, programming_interface)
> >>>>>
> >>>>> Signed-off-by: Ziye Yang <ziye.yang@intel.com>
> >>>>
> >>>> Since rte_pci is exposed to application this breaks the ABI.
> >>>
> >>> But applications are not going to be defining rte_pci_ids values internally, are
> >>> they? That is for drivers to use. Is this really an ABI breakage for applications that we
> >>> need to be concerned about?
> >>
> >> There might not be applications using it but drivers are ABI consumers
> >> too - think of 3rd party drivers and such.
> >
> > Drivers are not ABI consumers in the sense that ABI means
> > Application Binary Interface.
> > We are talking about drivers interface here.
> > When establishing the ABI policy we were discussing about applications only.
> 
> Generally speaking an ABI is an interface between two program (or 
> software if you like) modules, its not specific to "applications". 
> Looking at http://dpdk.org/doc/guides/contributing/versioning.html I see 
> it does only talk about applications, but an ABI consumer can also be 
> another library. A driver calling rte_malloc() is just as much 
> librte_eal ABI consumer as anything else.
> 
> Now, I understand that drivers use and need interface(s) that 
> applications have no use for or simply cannot use, and those interfaces 
> could be subject to different policies. As an extreme example, the Linux 
> kernel has two isolated ABIs, one is the userland system call interface 
> which is guaranteed to stay forever and the other is kernel module 
> interface, guarantees nothing at all.
> 
> In DPDK the difference is far muddier than that since all the interfaces 
> live in common, versioned userland DSOs. So if there are two different 
> interfaces following two different policies, it's all the more important 
> to clearly document them. One simple way could be using a different 
> prefix than rte_.

Good suggestion. Or we can simply have different files with a clear notice
in their headers and in the versioning doc.
It was well split in rte_cryptodev_pmd.h

> > I agree we must allow 3rd party drivers but there is no good reason
> > to try to upgrade DPDK without upgrading/porting the external drivers.
> > If someone does not want to release its driver and keep upgrading DPDK,
> > it is acceptable IMHO to force an upgrade of its driver.
> 
> Note that I've no particular sympathy for 3rd party drivers as such. 
> What I *do* care about is that breakage is made explicit, as in drivers 
> built for an incompatible version refuse to load at all, instead of 
> silently corrupting memory etc.

OK I agree.
Anyway the ABI versionning does not cover the structure changes.
What about making a DPDK version check when registering a driver?
So a binary driver would be clearly bound to a DPDK version.
And we should change or remove the .so version which never change for
most of drivers.