[Ksummit-discuss] Topic: Removal of code that is still in use by users but there is a better code.

Rafael J. Wysocki rjw at rjwysocki.net
Thu Jun 12 11:41:37 UTC 2014

On Wednesday, June 11, 2014 03:36:01 PM James Bottomley wrote:
> On Wed, 2014-06-11 at 15:26 -0700, Roland Dreier wrote:
> > On Wed, Jun 11, 2014 at 3:17 PM, James Bottomley
> > <James.Bottomley at hansenpartnership.com> wrote:
> > > This would eventually become like CONFIG_EXPERIMENTAL before somebody
> > > put it out of its misery: a pointless thing which everybody enables.
> > 
> > Probably so.
> > 
> > > Could we just step back and ask what the burning need to do this (at
> > > least for drivers; I understand the ABI deprecation headache) is?  Most
> > > driver code for obsolete things harmlessly compiles; why bother trying
> > > to hunt them down and shoot them when they're not really causing
> > > offence?
> > 
> > Every time a developer wants to change a core API, that developer
> > needs to patch every driver that uses the API.  Every old, unused,
> > bitrotten driver we have in the tree is 100% wasted work, and often a
> > substantial amount of work because it's really hard even to understand
> > how those drivers are (mis)using the API being changed.
> Well how often do we do that?  It's not like it's the most common
> activity.
> Even when we do it, mostly the changes are mechanical and no-one really
> notices.  On the odd occasion we have to change the call properties of
> the API (usually because of locking or layering problems) it forces the
> question of whether the driver is in use or not.  Mostly you don't
> change the API and put the driver under CONFIG_BROKEN to see if anyone
> turns up to claim it.
> In fact, we could document the above and call it our driver deprecation
> process.  I've done this occasionally in SCSI, but the fact it's so rare
> tends to make me think we don't really have that much of a problem.

I agree here.

Generally, if a kernel-wide change is being made for good reasons and something
gets in the way, it is a fair question to ask if that thing is actually used by
someone.  If it is not used by anyone, removing it may be regarded as part of
making the change.


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