Re: [dpdk-dev] git trees organization

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 9/13/2017 8:58 AM, Adrien Mazarguil wrote:
> Hi,
> 
> On Tue, Sep 12, 2017 at 09:32:07AM +0100, Bruce Richardson wrote:
>> On Tue, Sep 12, 2017 at 12:03:30AM +0200, Thomas Monjalon wrote:
>>> Hi all,
>>>
>>> As you know I am currently the only maintainer of the master tree.
>>> It is very convenient because I need to synchronize with others
>>> only when pulling "next-*" trees.
>>> But the drawback is that I should be available very often to
>>> avoid stalled patches waiting in patchwork backlog.
>>>
>>> I feel it is the good time to move to a slightly different organization.
>>> I am working closely with Ferruh Yigit for almost one year, as next-net
>>> maintainer, and I think it would be very efficient to delegate him some
>>> work for the master tree.
>>
>> I think Ferruh has been doing an excellent job on the net tree, and
>> would be an excellent candidate to help with the workload on the master
>> tree.
>>
>>> I mean that I would use the patchwork delegation to explicitly divide
>>> the workload given our different experiences.
>>> Ferruh, do you agree taking this new responsibility?
>>>
>>> At the same time, we can think how to add more git sub-trees:
>>
>> In principle, I'm in favour, but I think that the subtrees of the master
>> tree should be at a fairly coarse granularity, and not be too many of
>> them. The more subtrees, the more likely we are to have issues with
>> patchsets needing to be split across trees, or having to take bits from
>> multiple trees in order to test if everything is working.
> <snip>
> 
> About that, how about we start allowing true merge commits instead of
> rebasing (rewriting history) in order to ease things for maintainers?
> 
> This approach makes pull requests show up as a merge commits that contain
> the (ideally trivial) changes needed to resolve any conflicts; this has the
> following benefits:
> 
> - The work done by a maintainer during that merge is tracked, not silently
>   ignored or lost. The merge commit itself is signed-off by its author.
> 
> - This allows tracing mistakes or bugs to the conflict resolution itself.
> 
> - Upstream can reject pull requests on the basis that merging it is not
>   trivial enough (i.e. downstream must merge upstream changes first).
> 
> - Sub-trees can merge among themselves in case they need features that
>   encompass several trees, not necessarily always against the master
>   tree. Everything is tracked.
> 
> - Maintainers do not ever modify the commits they get from other trees,
>   which keep their SHAs unmodified as part of the history. A given commit ID
>   is truly unique among all trees (back-port trees remain the only exception
>   since commits are cherry-picked).
> 
> - It shifts the entire responsibility to the maintainers of sub-trees.
> 
> The only downside is that commits have several parents, history becomes a
> graph that developers need to get used to (some might call it a mess),
> however that's probably not an issue for those already used to Linux kernel
> development and other large projects.
> 
> I know this was already discussed in the past, however I think adding more
> sub-trees will make rebasing too complex otherwise>
> Thoughts?
>

Using git merge looks more proper git usage, but I have one question /
concern:

For next-net, sometimes there are dependent patches in main tree, and
what I am doing is rebasing sub-tree on top of latest main tree.

When switched to merge method, how dependent patches can be get into the
sub-tree? Merge from main tree to sub-tree? Won't this bidirectional
merging confusing?


And following are notes from my current experience:

- Having re-writable history gives some flexibility to sub-trees.
Possible to update commit logs and amend patches even after pushed.

- It is hard to confirm pulled commits in main tree, I guess merge
commit will make this easier.

- To track main tree, continuously rebasing and continuously re-writing
history, I am doing this almost daily, this may be hard for people
working on top of next-net.

- Conflict resolving done by sub-trees during rebase, instead of done by
main tree during merge. So this may be more distributed effort.

- Rebasing gives more straight forward history in main repo, merge
commits looks more confusing, although I would expect it won't be as
complex as Linux tree, so may not be a problem.

Thanks,
ferruh