Re: [dpdk-dev] [PATCH] doc: add deprecation notice on timer lib cleanup

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 09-May-19 8:05 AM, David Marchand wrote:
> On Thu, May 9, 2019 at 3:11 AM Stephen Hemminger 
> <stephen@networkplumber.org <mailto:stephen@networkplumber.org>> wrote:
> 
>     On Wed,  8 May 2019 17:48:06 -0500
>     Erik Gabriel Carrillo <erik.g.carrillo@intel.com
>     <mailto:erik.g.carrillo@intel.com>> wrote:
> 
>      > Due to an upcoming fix to allow the timer library to safely free its
>      > allocations during the finalize() call[1], an ABI change will be
>      > required. A new lock will be added to the rte_mem_config structure,
>      > which will be used by the timer library to synchronize init/finalize
>      > calls among multiple processes.
>      >
>      > [1] http://patches.dpdk.org/patch/53334/
>      >
>      > Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com
>     <mailto:erik.g.carrillo@intel.com>>
>      > ---
>      >  doc/guides/rel_notes/deprecation.rst | 4 ++++
>      >  1 file changed, 4 insertions(+)
>      >
>      > diff --git a/doc/guides/rel_notes/deprecation.rst
>     b/doc/guides/rel_notes/deprecation.rst
>      > index b47c8c2..7551383 100644
>      > --- a/doc/guides/rel_notes/deprecation.rst
>      > +++ b/doc/guides/rel_notes/deprecation.rst
>      > @@ -31,6 +31,10 @@ Deprecation Notices
>      >
>      >      + ``rte_eal_devargs_type_count``
>      >
>      > +* eal: the ``rte_mem_config`` struct will change to include a
>     new lock that
>      > +  will allow the timer subsystem to safely release its
>     allocations at cleanup
>      > +  time. This will result in an ABI break.
>      > +
>      >  * vfio: removal of ``rte_vfio_dma_map`` and
>     ``rte_vfio_dma_unmap`` APIs which
>      >    have been replaced with ``rte_dev_dma_map`` and
>     ``rte_dev_dma_unmap``
>      >    functions.  The due date for the removal targets DPDK 20.02.
> 
>     NAK
> 
>     Please go to the effort of making rte_mem_config not part of the
>     visible ABI.
>     Then change it.
> 
> 
> +1.

I agree on principle, however this won't solve the issue. It doesn't 
need to be externally visible, but that's not all of its problems - it's 
also shared between processes so there's an ABI contract between primary 
and secondary too. This means that, even if the structure itself is not 
public, any changes to it will still result in an ABI break. That's the 
nature of our shared memory.

In other words, if your goal is to avoid ABI breaks on changing this 
structure, making it internal won't help in the slightest.

-- 
Thanks,
Anatoly