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

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

[Konrad Rzeszutek Wilk]

Hey,

I would want to propose a topic on removing code in Linux that
users are using - but they are doing it less and less and it
mostly is tied in with older hardware. Specifically how to do
this transition properly - and if we want to define some checklist
/policy to do it via.

Specifically in the Xen virtualization world there is in pipeline code
that is going to obsolete some of the existing pvops code - and also
make lguest obsolete. It makes the Linux kernel run faster, less code to
deal with, makes x86 folks happy, and requires newer hardware.
This is known as PVH (ParaVirtualization Hardware).

So, from one hand - with newer hardware - we can remove some of the
code. On the other hand - with older hardware (pre EPT/NPT capable) or
low-powered ones  - we would making their life difficult and slower (as now
the hypervisor has to do the emulation, probably has some bugs, code
bitrotten, etc).

In essence it boils down to removing code in X years that users do use.

There is a nice migration path, but I am sure the moment we rip out the
code folks will come out of the woodwork, chase us down, and hit us with clubs.
I do enjoy hiking and don't want to have to look behind my back as I am
hiking.

What I want to propose is a topic to discuss what is the right way to do
this? I presume other platforms have had similar issues in the past (or
will be) and what is the best way of doing this. Are there any policies
in place?

P.S.
I say in pipeline because it is still experimental, the ABI hasn't been
bolted down, and we have tons of outstanding bugs before we let
enterprise customers take a stab at it, etc.

P.S.S.
Peter (hpa) is going to hate that I put 'X' instead of the '5' number. We
figured that in 5 years since we get this stable we can start the
count-down timer - but the 'getting' stable seems to take longer than I
am happy with (#@)@#$ bugs). Hence, X =  stable + 5. If there are any

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

[H. Peter Anvin]

On 06/10/2014 01:12 PM, Konrad Rzeszutek Wilk wrote:
> Hey,
> 
> I would want to propose a topic on removing code in Linux that
> users are using - but they are doing it less and less and it
> mostly is tied in with older hardware. Specifically how to do
> this transition properly - and if we want to define some checklist
> /policy to do it via.
> 

I second this.  Right now deprecation is entirely ad hoc... usually in
the form "this hasn't compiled for X releases and noone noticed", which
makes it hard to do *controlled* deprecation...

I realize this is a third rail kind of topic, but it puts us in really
hard spots as a project, sometime.

	-hpa

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

[josh]

On Tue, Jun 10, 2014 at 01:19:12PM -0700, H. Peter Anvin wrote:
> On 06/10/2014 01:12 PM, Konrad Rzeszutek Wilk wrote:
> > Hey,
> > 
> > I would want to propose a topic on removing code in Linux that
> > users are using - but they are doing it less and less and it
> > mostly is tied in with older hardware. Specifically how to do
> > this transition properly - and if we want to define some checklist
> > /policy to do it via.
> > 
> 
> I second this.  Right now deprecation is entirely ad hoc... usually in
> the form "this hasn't compiled for X releases and noone noticed", which
> makes it hard to do *controlled* deprecation...
> 
> I realize this is a third rail kind of topic, but it puts us in really
> hard spots as a project, sometime.

I agree.  I think we've had some recent examples of how to do this
better, with remap_file_pages: old userspace has to *work* on new
kernels, but it doesn't necessarily need to run fast, or integrate with
any new features.  We should deprecate more kernel bits in
favor of minimal compatibility layers, some of which we can associate
with old userspace and drop for new userspace.

- Josh Triplett

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

[H. Peter Anvin]

On 06/10/2014 05:36 PM, josh@joshtriplett.org wrote:
> 
> I agree.  I think we've had some recent examples of how to do this
> better, with remap_file_pages: old userspace has to *work* on new
> kernels, but it doesn't necessarily need to run fast, or integrate with
> any new features.  We should deprecate more kernel bits in
> favor of minimal compatibility layers, some of which we can associate
> with old userspace and drop for new userspace.
> 

Uhm... that applies only to a fairly restricted aspect of deprecation.
Much more is tied to specific hardware.

	-hpa

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

[Guenter Roeck]

On Tue, Jun 10, 2014 at 01:19:12PM -0700, H. Peter Anvin wrote:
> On 06/10/2014 01:12 PM, Konrad Rzeszutek Wilk wrote:
> > Hey,
> > 
> > I would want to propose a topic on removing code in Linux that
> > users are using - but they are doing it less and less and it
> > mostly is tied in with older hardware. Specifically how to do
> > this transition properly - and if we want to define some checklist
> > /policy to do it via.
> > 
> 
> I second this.  Right now deprecation is entirely ad hoc... usually in
> the form "this hasn't compiled for X releases and noone noticed", which
> makes it hard to do *controlled* deprecation...
> 
That is a bit different to "users are using but less and less". Personally 
I would not mind leaving code in the kernel as long as it is used, but
it would be great if we had some rule that a file/driver which did
not compile for X releases (pick a preferred number for X - two years 
worth of releases ?) can be removed.

Guenter

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

[Bjorn Helgaas]

On Wed, Jun 11, 2014 at 11:54 AM, Guenter Roeck <linux@roeck-us.net> wrote:
> On Tue, Jun 10, 2014 at 01:19:12PM -0700, H. Peter Anvin wrote:
>> On 06/10/2014 01:12 PM, Konrad Rzeszutek Wilk wrote:
>> > Hey,
>> >
>> > I would want to propose a topic on removing code in Linux that
>> > users are using - but they are doing it less and less and it
>> > mostly is tied in with older hardware. Specifically how to do
>> > this transition properly - and if we want to define some checklist
>> > /policy to do it via.
>> >
>>
>> I second this.  Right now deprecation is entirely ad hoc... usually in
>> the form "this hasn't compiled for X releases and noone noticed", which
>> makes it hard to do *controlled* deprecation...
>>
> That is a bit different to "users are using but less and less". Personally
> I would not mind leaving code in the kernel as long as it is used, but
> it would be great if we had some rule that a file/driver which did
> not compile for X releases (pick a preferred number for X - two years
> worth of releases ?) can be removed.

I suspect most people would agree with the idea that something that
hasn't compiled for X years can be removed, possibly with some
negotiation about what X is.

But my impression is the proposal is to go farther than that, and
figure out a way to remove obsolete but still-compilable code.  If we
all did our jobs perfectly, we would never add a change to Linux that
broke compilation of anything.  So if there's a file that doesn't
compile anymore, I think of that as a result of a mistake somewhere
along the line.  We can use that mistake to deduce that nobody cares
anymore, but it'd be a lot nicer to have a scheme that didn't depend
on people making random mistakes.

Bjorn

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

[josh]

On Wed, Jun 11, 2014 at 08:56:44AM -0700, H. Peter Anvin wrote:
> On 06/10/2014 05:36 PM, josh@joshtriplett.org wrote:
> > 
> > I agree.  I think we've had some recent examples of how to do this
> > better, with remap_file_pages: old userspace has to *work* on new
> > kernels, but it doesn't necessarily need to run fast, or integrate with
> > any new features.  We should deprecate more kernel bits in
> > favor of minimal compatibility layers, some of which we can associate
> > with old userspace and drop for new userspace.
> > 
> 
> Uhm... that applies only to a fairly restricted aspect of deprecation.
> Much more is tied to specific hardware.

Agreed; hardware support does not have the same degree of compatibility
concerns that userspace interfaces do.

For instance, we could reasonably ask whether we can deprecate support
for ancient filesystems and push that code into FUSE in userspace, given
that most such filesystems only exist for forensics rather than
performance.  That would mitigate potential exploits in that code.

- Josh Triplett

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

[Stephen Rothwell]

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Hi Bjorn,

On Wed, 11 Jun 2014 13:43:18 -0600 Bjorn Helgaas <bhelgaas@google.com> wrote:
>
> all did our jobs perfectly, we would never add a change to Linux that
> broke compilation of anything.  So if there's a file that doesn't
> compile anymore, I think of that as a result of a mistake somewhere
> along the line.  We can use that mistake to deduce that nobody cares
> anymore, but it'd be a lot nicer to have a scheme that didn't depend
> on people making random mistakes.

We could start making nonrandom mistakes? ;-)

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au

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

[Andy Lutomirski]

On Wed, Jun 11, 2014 at 2:53 PM, Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> Hi Bjorn,
>
> On Wed, 11 Jun 2014 13:43:18 -0600 Bjorn Helgaas <bhelgaas@google.com> wrote:
>>
>> all did our jobs perfectly, we would never add a change to Linux that
>> broke compilation of anything.  So if there's a file that doesn't
>> compile anymore, I think of that as a result of a mistake somewhere
>> along the line.  We can use that mistake to deduce that nobody cares
>> anymore, but it'd be a lot nicer to have a scheme that didn't depend
>> on people making random mistakes.
>
> We could start making nonrandom mistakes? ;-)

How about adding CONFIG_DELETED_THINGS.  If you enable it, you get a
message asking you to speak up if you actually need anything in there.
CONFIG_DELETED_THINGS would default to n, and the new (and temporary)
things under it would also default to n.

Think feature-removal-schedule, but with teeth.

--Andy

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

[James Bottomley]

On Wed, 2014-06-11 at 15:01 -0700, Andy Lutomirski wrote:
> On Wed, Jun 11, 2014 at 2:53 PM, Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> > Hi Bjorn,
> >
> > On Wed, 11 Jun 2014 13:43:18 -0600 Bjorn Helgaas <bhelgaas@google.com> wrote:
> >>
> >> all did our jobs perfectly, we would never add a change to Linux that
> >> broke compilation of anything.  So if there's a file that doesn't
> >> compile anymore, I think of that as a result of a mistake somewhere
> >> along the line.  We can use that mistake to deduce that nobody cares
> >> anymore, but it'd be a lot nicer to have a scheme that didn't depend
> >> on people making random mistakes.
> >
> > We could start making nonrandom mistakes? ;-)
> 
> How about adding CONFIG_DELETED_THINGS.  If you enable it, you get a
> message asking you to speak up if you actually need anything in there.
> CONFIG_DELETED_THINGS would default to n, and the new (and temporary)
> things under it would also default to n.
> 
> Think feature-removal-schedule, but with teeth.

This would eventually become like CONFIG_EXPERIMENTAL before somebody
put it out of its misery: a pointless thing which everybody enables.

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?

James

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

[Roland Dreier]

On Wed, Jun 11, 2014 at 3:17 PM, James Bottomley
<James.Bottomley@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.

 - R.

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

[James Bottomley]

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@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.

James

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

[Guenter Roeck]

On 06/11/2014 12:43 PM, Bjorn Helgaas wrote:
> On Wed, Jun 11, 2014 at 11:54 AM, Guenter Roeck <linux@roeck-us.net> wrote:
>> On Tue, Jun 10, 2014 at 01:19:12PM -0700, H. Peter Anvin wrote:
>>> On 06/10/2014 01:12 PM, Konrad Rzeszutek Wilk wrote:
>>>> Hey,
>>>>
>>>> I would want to propose a topic on removing code in Linux that
>>>> users are using - but they are doing it less and less and it
>>>> mostly is tied in with older hardware. Specifically how to do
>>>> this transition properly - and if we want to define some checklist
>>>> /policy to do it via.
>>>>
>>>
>>> I second this.  Right now deprecation is entirely ad hoc... usually in
>>> the form "this hasn't compiled for X releases and noone noticed", which
>>> makes it hard to do *controlled* deprecation...
>>>
>> That is a bit different to "users are using but less and less". Personally
>> I would not mind leaving code in the kernel as long as it is used, but
>> it would be great if we had some rule that a file/driver which did
>> not compile for X releases (pick a preferred number for X - two years
>> worth of releases ?) can be removed.
>
> I suspect most people would agree with the idea that something that
> hasn't compiled for X years can be removed, possibly with some
> negotiation about what X is.
>
> But my impression is the proposal is to go farther than that, and
> figure out a way to remove obsolete but still-compilable code.  If we
> all did our jobs perfectly, we would never add a change to Linux that
> broke compilation of anything.  So if there's a file that doesn't
> compile anymore, I think of that as a result of a mistake somewhere
> along the line.  We can use that mistake to deduce that nobody cares
> anymore, but it'd be a lot nicer to have a scheme that didn't depend
> on people making random mistakes.
>

I understand, but personally I don't have much problem with code as long
as it compiles. I am more concerned with code that doesn't compile and
no one cared for years.

Sure, there is a difference if that code actually consumes cycles, but I
suspect that isn't likely enough to be bothered about. If there is such code,
I would agree that it should be removed even if it does compile.

Guenter

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

[H. Peter Anvin]

On 06/11/2014 10:54 AM, Guenter Roeck wrote:
> That is a bit different to "users are using but less and less". Personally 
> I would not mind leaving code in the kernel as long as it is used, but
> it would be great if we had some rule that a file/driver which did
> not compile for X releases (pick a preferred number for X - two years 
> worth of releases ?) can be removed.

This is the problem, though: the code can easily compile well past the
point of anyone using it, because well-meaning maintainers is keeping it
from falling apart completely, often at substantial cost.

	-hpa

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

[Steven Rostedt]

On Wed, 11 Jun 2014 16:22:16 -0700
Guenter Roeck <linux@roeck-us.net> wrote:


> 
> I understand, but personally I don't have much problem with code as long
> as it compiles. I am more concerned with code that doesn't compile and
> no one cared for years.

Matters what your definition of "doesn't compile" is.

You may not have the right config option set to make it compile.
randconfig builds trigger failed compiles quite often. Is that code
worth removing?

As most people test allyesconfig and allmodconfig quite a bit, I'm not
sure what code you are talking about. Basically everything that gets
enabled does compile.

Of course, if you set something to CONFIG_BROKEN and no one complains
for a few years, that's worth nuking.

-- Steve

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

[Geert Uytterhoeven]

On Thu, Jun 12, 2014 at 4:48 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 11 Jun 2014 16:22:16 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
>> I understand, but personally I don't have much problem with code as long
>> as it compiles. I am more concerned with code that doesn't compile and
>> no one cared for years.

And once it stops compiling, more issues will be introduced into that area,
which no one notices due to the first compile failure.

> Matters what your definition of "doesn't compile" is.
>
> You may not have the right config option set to make it compile.
> randconfig builds trigger failed compiles quite often. Is that code
> worth removing?
>
> As most people test allyesconfig and allmodconfig quite a bit, I'm not
> sure what code you are talking about. Basically everything that gets
> enabled does compile.

And once it compiles, it usually works!

I have the impression we're getting good (read: having good review) at doing
logical changes, i.e. when code is integrated, it works (almost always :-).
The tricky parts these days are configuration issues, i.e. code that fails to
build for certain configurations, due to various reasons (forgot to handle a
case in another #ifdef branch, code inside vs. outside #ifdef,
different indirect
includes on different architectures, ...). Fortunately the latter can be caught
using more CPU resources, in contrast with more reviewers for the former.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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

[Rafael J. Wysocki]

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@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.

Rafael

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

[John W. Linville]

On Wed, Jun 11, 2014 at 03:36:01PM -0700, 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@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.

I think it happens often enough to be a valid concern.  There are
definitely wireless drivers (some which predate my tenure), that
still compile but which I strongly doubt are functional or used.
I've pushed some out of the tree from time to time, and I'll probably
continue to do so.  But in the meantime, it can be difficult to judge
what is used or not and what simply doesn't work because of a series
of subtle mistakes in patch bombs...

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.

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

[James Bottomley]

On Thu, 2014-06-12 at 09:27 -0400, John W. Linville wrote:
> On Wed, Jun 11, 2014 at 03:36:01PM -0700, 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@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.
> 
> I think it happens often enough to be a valid concern.  There are
> definitely wireless drivers (some which predate my tenure), that
> still compile but which I strongly doubt are functional or used.
> I've pushed some out of the tree from time to time, and I'll probably
> continue to do so.  But in the meantime, it can be difficult to judge
> what is used or not and what simply doesn't work because of a series
> of subtle mistakes in patch bombs...

So the solution to this is to put the drivers into a freeze maintenance
mode where you make no changes but what is absolutely required (and you
can decide depending on the extensiveness of the required change whether
you'd rather mark the driver as BROKEN than do the API change).  It
doesn't solve the problem entirely but it means that breakage has to
come from outside rather than subtle mistakes in unnecessary patches.

James

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

[Linus Walleij]

On Thu, Jun 12, 2014 at 12:36 AM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Wed, 2014-06-11 at 15:26 -0700, Roland Dreier wrote:

>> 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.

Well I'm doing that right now in the GPIO subsystem where I'm
refactoring all local irqchip implementations into the gpiolib.

So I attack-patch all suitable refactoring targets, indeed. And
sometimes the answer comes back "I don't have that hardware
anymore, cannot test it", even from the person listed as maintainer.
(drivers/gpio/gpio-adnp.c, drivers/pinctrl/spear/*)

And then I get a strong urge to delete it, because a maintainer that
can't maintain is not much of a maintainer...

Yours,
Linus Walleij