Re: Linux XIA - merge proposal

[Bjorn Helgaas]

[+cc Arnd]

On Fri, Mar 20, 2015 at 1:46 PM, Michel Machado <michel@xxxxxxxxxxxxxxx> wrote:
> On 03/18/2015 06:27 AM, Oded Gabbay wrote:
>> Hi Michel,
>> If you want an example of how to break a fairly medium+
>> code-base/driver, I believe amdkfd is a good example. Originally, I had
>> dumped 80+ patches, but after getting some flames & help from drm devs,
>> I rearranged them into a nicely 25 patches:
>>
>> 1. Several patches that implements helper functions in other drivers
>> (mm, iommu, radeon)
>> 2. Patch to add IOCTL definitions (kfd_ioctl.h)
>> 3. Patch to add skeleton code base of driver
>> 4. Several patches that add different modules in the amdkfd driver
>> 5. Several patches that implement the IOCTLs in the amdkfd drivers
>>
>> See this link for the final set that was merged into 3.19-rc1:
>> http://cgit.freedesktop.org/~gabbayo/linux/?h=amdkfd-v6
>>
>> Take a look from commit "Merge branch 'drm-next-3.19'  to the HEAD of
>> the log.
>>
>> If you need additional advice, you can contact me.
>>
>>      Oded
>
> Hi Oded,
>
>    Thank you for your example. After thinking on how to get our repository
> as a set of patches, it became clear that I have to start with a new
> repository and gradually move the code from our current repository to this
> new one. Because the commits of the current repository follows how we
> arrived where we are now, and this makes the goal of only reviewing the
> final code harder.

I agree that people likely won't want to review the entire trail of
how you got to where you are now.

>    I'm going to take advantage that Linux XIA is broken down into kernel
> modules, and have a serie of patches for each module. With the exception of
> the core module, on which all other modules depend, all modules don't have
> dependencies between them. The problem I'm running into with this approach
> is that some patches will be large. For example, the core module has these
> files:
>
> $ wc net/xia/*.c
>    744   2246  15523 net/xia/dag.c
>    897   2378  23006 net/xia/fib.c
>    360 931 8240 net/xia/fib_frontend.c
>     72    169   1486 net/xia/locktbl.c
>    106    259   2116 net/xia/main.c
>    281 858 7241 net/xia/output.c
>   1471   4573  37952 net/xia/route.c
>    598   1579  13783 net/xia/socket.c
>    109    305   2852 net/xia/vxidty.c
>   4638  13298 112199 total
>
>    I can try to break these large patches into smaller ones, but this would
> likely break code coherence since each module is supposed to self-contained.

We try very hard to make sure that the kernel is buildable and
functional after every commit, even if that commit is part of a larger
series.  This helps people bisect to find regressions.  Just something
to keep in mind when breaking things up.

> My understanding is that you created skeletons to gradually fill them in to
> address similar issue, but I'm not sure how to do it in my case.

This problem sounds similar to that of adding a new processor
architecture.  I cc'd Arnd, since he's helped do that several times.
Here's how one recent architecture was added (from [1]):

  nios2: Build infrastructure
  nios2: Assembly macros and definitions
  nios2: Kernel booting and initialization
  nios2: Exception handling
  nios2: Traps exception handling
  nios2: Memory management
  nios2: I/O Mapping
  nios2: MMU Fault handling
  nios2: Page table management
  nios2: Process management
  nios2: Cache handling
  nios2: TLB handling
  nios2: Interrupt handling
  nios2: DMA mapping API
  nios2: ELF definitions
  nios2: System calls handling
  nios2: Signal handling support
  nios2: Library functions
  nios2: Device tree support
  nios2: Time keeping
  nios2: Cpuinfo handling
  nios2: Miscellaneous header files
  nios2: Nios2 registers
  nios2: Module support
  nios2: ptrace support
  Add ELF machine define for Nios2
  MAINTAINERS: Add nios2 maintainer
  Documentation: Add documentation for Nios2 architecture

Bjorn

[1] http://lkml.kernel.org/r/1397824031-4892-1-git-send-email-lftan@xxxxxxxxxx
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