Re: Various changes "backportability"

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, 13 Sept 2023 at 04:13, Michael Tokarev <mjt@tls.msk.ru> wrote:
>
> [Added some more active patch reviewers to Cc]
>
> Hi!
>
> Yesterday I wrote email about picking up changes from master
> for previous stable release(s).  What's interesting is that
> yesterday, basically in a single day, we've faced numerous
> examples of subsystem changes which makes such backporting
> significantly more difficult than might be.
>
> For example, recent tpm bugfix, which is trivial by its own,
> uses RETRY_ON_EINTR helper which were introduced recently and
> which is now used everywhere.  coroutine_fn et al markers is
> another example, translator_io_start is yet another, and so
> on and so on.
>
> When adding such subsystems/helpers which are to be used widely,
> please split the initial implementation patch out of a single
> "introduce foo; convert everything to use it" change.  Instead,
> add the feature in a small patch first, and convert all users
> tree-wide to it in a second, subsequent patch, maybe removing
> the old version in that second patch too.  Where it makes sense
> ofcourse, - sometimes it is not possible or just complicated to
> do that, like when old and new implementations can't be supported
> in parallel.
>
> Just by splitting "introduce" from "convert", especially for
> something simple which will be used all around, you'll greatly
> simplify stable trees maintenance.

The general concept makes sense to me but I'm not sure what the
specific issue with adding (?) coroutine_fn was. Can you link to the
patch that caused difficulties so I can review it?

Thanks,
Stefan