On 6/19/15 9:16 AM, Thomas Monjalon wrote: > 2015-06-19 09:02, Neil Horman: >> On Fri, Jun 19, 2015 at 02:32:33PM +0200, Thomas Monjalon wrote: >>> 2015-06-19 06:26, Neil Horman: >>>> On Thu, Jun 18, 2015 at 04:55:45PM +0000, O'Driscoll, Tim wrote: >>>>> For the 2.1 release, I think we should agree to make patches that change >>>>> the ABI controllable via a compile-time option. I like Olivier's proposal >>>>> on using a single option (CONFIG_RTE_NEXT_ABI) to control all of these >>>>> changes instead of a separate option per patch set (see >>>>> http://dpdk.org/ml/archives/dev/2015-June/019147.html), so I think we >>>>> should rework the affected patch sets to use that approach for 2.1. >>>> >>>> This is a bad idea. Making ABI dependent on compile time options isn't a >>>> maintainable solution. It breaks the notion of how LIBABIVER is supposed >>>> to >>>> work (that is to say you make it impossible to really tell what ABI >>>> version you >>>> are building). >>> >>> The idea was to make LIBABIVER increment dependent of CONFIG_RTE_NEXT_ABI. >>> So one ABI version number refers always to the same ABI. >>> >>>> If you have two compile time options that modify the ABI, you >>>> have to burn through 4 possible LIBABIVER version values to accomodate all >>>> possible combinations, and then you need to remember that when you make >>>> them >>>> statically applicable. >>> >>> The idea is to have only 1 compile-time option: CONFIG_RTE_NEXT_ABI. >>> >>> Your intent when introducing ABI policy was to allow smooth porting of >>> applications from a DPDK version to another. Right? >>> The adopted solution was to provide backward compatibility during 1 release. >>> But there are cases where it's not possible. So the policy was to notice >>> the future change and wait one release cycle to break the ABI (failing >>> compatibility goals). >>> The compile-time option may provide an alternative DPDK packaging when the >>> ABI backward compatibility cannot be provided (case of mbuf changes). >>> In such case, it's still possible to upgrade DPDK by providing 2 versions of >>> DPDK libs. So the existing apps continue to link with the previous ABI and >>> have the possibility of migrating to the new one. >>> Another advantage of this approach is that we don't have to wait 1 release >>> to integrate the changes. >>> The last advantage is to benefit early of these changes with static >>> libraries. >> >> Hm, ok, thats a bit more reasonable, but it still seems shaky to me. >> Implementing an ABI preview option like this implies the notion that, after a >> release, you have to remove all the ifdefs that you inserted to create the >> new >> ABI. That seems like an easy task, but it becomes a pain when the ABI delta >> is >> large, and is predicated on the centralization of work effort (that is to say >> you need to identify someone to submit the 'remove the NEXT_ABI config ifdefs >> from the build' patch every release. > > It won't be so huge if we reserve the NEXT_ABI solution to changes which > cannot > have easy backward compatibility with the compat macros you introduced. > I feel I can do the job of removing the ifdefs NEXT_ABI after each release. > At the same time, the deprecated API, using the compat macros, will be > removed. > >> What might be better would be a dpdk-next branch (or even a dpdk-next tree, >> of >> the sort that Thomas Herbert proposed a few weeks ago). > > This tree was created after Thomas' request: > http://dpdk.org/browse/next/dpdk-next/
Thomas, I am sorry if I went quiet for awhile but I was on personal travel with inconsistent access so I almost missed most of this discussion about ABI changes. My understanding of the purpose of the dpdk-next tree is to validate patches by applying and compiling against a "pull" from the main dpdk tree. I think a good way to handle ABI change while effectively using the dpdk-next might be to do as follows: Create a specific branch for the new ABI such as 2.X in the main dpdk tree. Once that 2.X branch is created, dpdk-next would mirror the 2.X branch along with master. Since, dpdk-next would also have the 2.X branch that is in the main dpdk tree, submitted patches could be applied to either the main branch or the new-ABI 2.X branch. Providing that patch submitters make it clear whether a submitted patch is for the new ABI or the old ABI, dpdk-next could continue to validate the patches for either the main branch or the new ABI 2.X branch. > >> Patches that aren't ABI stable can be put on the next-branch/tree in thier >> final format. You can delcare the branch unstable (thereby reserving your >> right to rebase it). People can use that to preview the next ABI version >> (complete with the update LIBABIVER bump), and when you release dpdk-X, >> the new ABI for dpdk-X+1 is achieved by simply merging. > > Having this tree living would be a nice improvement but it won't provide any > stable (and enough validated) releases to rely on. >
