[Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Jean-Michel Hautbois]

Hi !

I have a 3.18 kernel which is currently built with xenomai 2.6.4.
I need to keep xenomai 2.6.4, as a lot of applications are using the API,
and I don't want to migrate, the cost would be very high ATM.

What is the best strategy to migrate xenomai to a 4.6 kernel ?
Would you be interested by the patches once done ?

Thanks,
JM

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Gilles Chanteperdrix]

On Fri, Jun 03, 2016 at 10:06:10AM +0200, Jean-Michel Hautbois wrote:
> Hi !
> 
> I have a 3.18 kernel which is currently built with xenomai 2.6.4.
> I need to keep xenomai 2.6.4, as a lot of applications are using the API,
> and I don't want to migrate, the cost would be very high ATM.

The APIs have not changed much. The cost is not very high. The
changes are documented here:
https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/

> 
> What is the best strategy to migrate xenomai to a 4.6 kernel ?

You will have to:
- port the I-pipe patch for Linux 4.1 to Linux 4.6
- add to the I-pipe patches the "I-pipe legacy" support, which was
removed from 4.1
- add the missing bits to Xenomai to adapt to the kernel API changes
between Linux 3.18 and Linux 4.6, of which there should be a fair
amount, given the difference in version numbers.

So, the best strategy is to not migrate xenomai 2.6.4 to a 4.6
kernel.

> Would you be interested by the patches once done ?

No. Xenomai 2.6.5 is about to be released, will not support 4.x
kernel, and will be the last release in the 2.6 branch. We simply do
not have the man power to maintain two branches, and for this
reason, want to encourage the users to migrate.

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Lennart Sorensen]

On Fri, Jun 03, 2016 at 10:06:10AM +0200, Jean-Michel Hautbois wrote:
> Hi !
> 
> I have a 3.18 kernel which is currently built with xenomai 2.6.4.
> I need to keep xenomai 2.6.4, as a lot of applications are using the API,
> and I don't want to migrate, the cost would be very high ATM.
> 
> What is the best strategy to migrate xenomai to a 4.6 kernel ?
> Would you be interested by the patches once done ?

Well I managed to take the ipipe for 4.1 and then add xenomai-2.6 latest
git to that and with just a couple of minor tweaks the patches applied
and built and seemed to pass all the tests I threw at it.  I can't
imagine 4.4 would be much harder than 4.1, although I didn't check if
ipipe work had been done for 4.4 yet.  Didn't get a chance to full test
it though and I moved to a new job a few weeks ago, so I don't have the
code handy either unfortunately (although I could probably ask for it).

-- 
Len Sorensen

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Lennart Sorensen]

On Fri, Jun 03, 2016 at 11:13:39AM +0200, Gilles Chanteperdrix wrote:
> The APIs have not changed much. The cost is not very high. The
> changes are documented here:
> https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/
> 
> You will have to:
> - port the I-pipe patch for Linux 4.1 to Linux 4.6

Would that not be required for xenomai 3.x as well though?

> - add to the I-pipe patches the "I-pipe legacy" support, which was
> removed from 4.1
> - add the missing bits to Xenomai to adapt to the kernel API changes
> between Linux 3.18 and Linux 4.6, of which there should be a fair
> amount, given the difference in version numbers.
> 
> So, the best strategy is to not migrate xenomai 2.6.4 to a 4.6
> kernel.
> 
> > Would you be interested by the patches once done ?
> 
> No. Xenomai 2.6.5 is about to be released, will not support 4.x
> kernel, and will be the last release in the 2.6 branch. We simply do
> not have the man power to maintain two branches, and for this
> reason, want to encourage the users to migrate.

That does make sense.

Of course a lot of people are scared of moving xenomai versions.  3 sounds
quite different than 2.6, and I certainly remember having a fair bit of
pain going from 2.5 to 2.6 years ago (some of it was probably self inflicted).

-- 
Len Sorensen

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Gilles Chanteperdrix]

On Fri, Jun 03, 2016 at 09:55:34AM -0400, Lennart Sorensen wrote:
> On Fri, Jun 03, 2016 at 11:13:39AM +0200, Gilles Chanteperdrix wrote:
> > The APIs have not changed much. The cost is not very high. The
> > changes are documented here:
> > https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/
> > 
> > You will have to:
> > - port the I-pipe patch for Linux 4.1 to Linux 4.6
> 
> Would that not be required for xenomai 3.x as well though?
> 
> > - add to the I-pipe patches the "I-pipe legacy" support, which was
> > removed from 4.1
> > - add the missing bits to Xenomai to adapt to the kernel API changes
> > between Linux 3.18 and Linux 4.6, of which there should be a fair
> > amount, given the difference in version numbers.
> > 
> > So, the best strategy is to not migrate xenomai 2.6.4 to a 4.6
> > kernel.
> > 
> > > Would you be interested by the patches once done ?
> > 
> > No. Xenomai 2.6.5 is about to be released, will not support 4.x
> > kernel, and will be the last release in the 2.6 branch. We simply do
> > not have the man power to maintain two branches, and for this
> > reason, want to encourage the users to migrate.
> 
> That does make sense.
> 
> Of course a lot of people are scared of moving xenomai versions.  3 sounds
> quite different than 2.6, and I certainly remember having a fair bit of
> pain going from 2.5 to 2.6 years ago (some of it was probably self inflicted).

As far as I remember there were almost no API changes between 2.5
and 2.6. The main reason to switch from 2.5 to 2.6 was to fix an
issue that could not be fixed reasonably without breaking the ABI.

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Jean-Michel Hautbois]

Hi,

2016-06-03 16:09 GMT+02:00 Gilles Chanteperdrix <
gilles.chanteperdrix@xenomai.org>:

> On Fri, Jun 03, 2016 at 09:55:34AM -0400, Lennart Sorensen wrote:
> > On Fri, Jun 03, 2016 at 11:13:39AM +0200, Gilles Chanteperdrix wrote:
> > > The APIs have not changed much. The cost is not very high. The
> > > changes are documented here:
> > > https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/
> > >
> > > You will have to:
> > > - port the I-pipe patch for Linux 4.1 to Linux 4.6
> >
> > Would that not be required for xenomai 3.x as well though?
> >
> > > - add to the I-pipe patches the "I-pipe legacy" support, which was
> > > removed from 4.1
> > > - add the missing bits to Xenomai to adapt to the kernel API changes
> > > between Linux 3.18 and Linux 4.6, of which there should be a fair
> > > amount, given the difference in version numbers.
> > >
> > > So, the best strategy is to not migrate xenomai 2.6.4 to a 4.6
> > > kernel.
> > >
> > > > Would you be interested by the patches once done ?
> > >
> > > No. Xenomai 2.6.5 is about to be released, will not support 4.x
> > > kernel, and will be the last release in the 2.6 branch. We simply do
> > > not have the man power to maintain two branches, and for this
> > > reason, want to encourage the users to migrate.
> >
> > That does make sense.
>
>
>From a maintenance point of view, it definitely makes sense.
So, perhaps the best is to try out mercury and use only PREEMPT-RT patches
on the kernel side, along with the compat layer on the userspace side...


> > Of course a lot of people are scared of moving xenomai versions.  3
> sounds
> > quite different than 2.6, and I certainly remember having a fair bit of
> > pain going from 2.5 to 2.6 years ago (some of it was probably self
> inflicted).
>
> As far as I remember there were almost no API changes between 2.5
> and 2.6. The main reason to switch from 2.5 to 2.6 was to fix an
> issue that could not be fixed reasonably without breaking the ABI.
>

I am scared by the compatibility between the existing  2.6 and the
now-to-be-used 3.x.

JM

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Lennart Sorensen]

On Fri, Jun 03, 2016 at 04:09:59PM +0200, Gilles Chanteperdrix wrote:
> As far as I remember there were almost no API changes between 2.5
> and 2.6. The main reason to switch from 2.5 to 2.6 was to fix an
> issue that could not be fixed reasonably without breaking the ABI.

Well it was years ago so I can't even recall what was causing problems
anymore.

-- 
Len Sorensen

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Gilles Chanteperdrix]

On Fri, Jun 03, 2016 at 11:13:39AM +0200, Gilles Chanteperdrix wrote:
> - add to the I-pipe patches the "I-pipe legacy" support, which was
> removed from 4.1

The I-pipe legacy support is still there in the I-pipe patch for
Linux 4.1

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Gilles Chanteperdrix]

On Fri, Jun 03, 2016 at 04:20:23PM +0200, Jean-Michel Hautbois wrote:
> I am scared by the compatibility between the existing  2.6 and the
> now-to-be-used 3.x.

As I said, the migration process is documented:
https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/

And not all that scary at all.

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] Migrating a Xenomai 2.6.4 to a 4.6 kernel

[Philippe Gerum]

On 06/03/2016 04:20 PM, Jean-Michel Hautbois wrote:
> Hi,
> 
> 2016-06-03 16:09 GMT+02:00 Gilles Chanteperdrix <
> gilles.chanteperdrix@xenomai.org>:
> 
>> On Fri, Jun 03, 2016 at 09:55:34AM -0400, Lennart Sorensen wrote:
>>> On Fri, Jun 03, 2016 at 11:13:39AM +0200, Gilles Chanteperdrix wrote:
>>>> The APIs have not changed much. The cost is not very high. The
>>>> changes are documented here:
>>>> https://xenomai.org/migrating-from-xenomai-2-x-to-3-x/
>>>>
>>>> You will have to:
>>>> - port the I-pipe patch for Linux 4.1 to Linux 4.6
>>>
>>> Would that not be required for xenomai 3.x as well though?
>>>
>>>> - add to the I-pipe patches the "I-pipe legacy" support, which was
>>>> removed from 4.1
>>>> - add the missing bits to Xenomai to adapt to the kernel API changes
>>>> between Linux 3.18 and Linux 4.6, of which there should be a fair
>>>> amount, given the difference in version numbers.
>>>>
>>>> So, the best strategy is to not migrate xenomai 2.6.4 to a 4.6
>>>> kernel.
>>>>
>>>>> Would you be interested by the patches once done ?
>>>>
>>>> No. Xenomai 2.6.5 is about to be released, will not support 4.x
>>>> kernel, and will be the last release in the 2.6 branch. We simply do
>>>> not have the man power to maintain two branches, and for this
>>>> reason, want to encourage the users to migrate.
>>>
>>> That does make sense.
>>
>>
>>From a maintenance point of view, it definitely makes sense.
> So, perhaps the best is to try out mercury and use only PREEMPT-RT patches
> on the kernel side, along with the compat layer on the userspace side...
> 
> 
>>> Of course a lot of people are scared of moving xenomai versions.  3
>> sounds
>>> quite different than 2.6, and I certainly remember having a fair bit of
>>> pain going from 2.5 to 2.6 years ago (some of it was probably self
>> inflicted).
>>
>> As far as I remember there were almost no API changes between 2.5
>> and 2.6. The main reason to switch from 2.5 to 2.6 was to fix an
>> issue that could not be fixed reasonably without breaking the ABI.
>>
> 
> I am scared by the compatibility between the existing  2.6 and the
> now-to-be-used 3.x.
> 

If you have any specific example of incompatibilities breaking your
current design, please let us know. If your application has been using
the POSIX or "native" Xenomai 2.6 API so far, with drivers based on
RTDM, you should not find any.

To clarify the Xenomai project's stance on these matters, we discourage
people from basing _new_ projects on the Xenomai 2.6.x series (or
earlier, obviously). Those projects should start with 3.x, because it is
actively maintained and developed, whereas 2.6.x is officially EOL.

However, some production-grade projects already deployed which have to
stick with Xenomai 2.6.x may want to upgrade to Linux 4.x. For this
reason, I pushed the commits  required to build the upcoming Xenomai
2.6.5 against Linux 4.1. However, those projects will be on their own
with respect to maintaining the Xenomai 2.6.x + I-pipe combo for kernel
releases beyond 4.1.

-- 
Philippe.