On Fri, 2009-10-02 at 21:25 +0200, Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
> > Philippe Gerum wrote:
> >> On Tue, 2009-09-29 at 19:31 +0200, Gilles Chanteperdrix wrote:
> >>> Hi guys,
> >>>
> >>> full of energy after this tremendous first XUM,
> >> Agreed, thanks to the DENX folks for having thought of it in the first
> >> place, and organized it nicely.
> >>
> >>>  I would like to start a
> >>> discussion about what people would like to see in the 2.5 branch.
> >>>
> >> Jan has described the situation quite accurately already, regarding the
> >> trade-off between getting everything we want into 2.5 so that no 2.6 is
> >> required, and releasing the too long-awaited 2.5 asap.
> >>
> >> As you mentioned already, the key issue is ABI stability.
> >> Any change we want before 3.0 that breaks the ABI should preferably go
> >> to 2.5, so that we don't end up maintaining 2.5.x, 2.6.x and 3.x. At any
> >> rate, we could not afford the latter anyway. This is a different matter
> >> than API issues; we already allowed API extensions during a stable
> >> cycle, provided they do not break existing application code (except in
> >> emergency cases), so I see no problem in pushing a few more services to
> >> 2.5.1 and beyond, provided that condition is met.
> >>
> >>> Here is a first list, please feel free to criticize it:
> >>> - signals in primary domain (something that we almost forgot)
> >> Yes, this one must be in. At least, we should break the ABI one more
> >> time for this before releasing 2.5.0. This item has priority #1 for
> >> me, since providing that infrastructure will enable a series of
> >> additional services to be implemented properly. In fact, this is more a
> >> matter of allowing nucleus callouts to user-space than anything else;
> >> POSIX RT signals in full primary mode being an application of them.
> > 
> > Ok. So, if we add the core skin fdtable, this leaves us with two items:
> > - signals in primary domain
> Sorry, I neither see the need nor feel comfortable about the impact /
> side effects of such an extension.

This extension is mandatory to allow callouts from the nucleus to a
user-space application without forcing the latter to leave primary mode.
This is direly needed when implementing some legacy RTOS services, and
currently only available from kernel to kernel. We need this 1) to
implement POSIX RT signals (a long term maintenance release like 2.5
must have those), 2) implement missing services from existing skins
(VxWorks comes to mind), 3) provide an upgrade path from 2.5.x to 3.x,
for people who will have to move their apps to userland in v3, and as
such should be able to anticipate that move with 2.5.

The impact is minimal, we have discussed the general idea in a previous
thread actually. This is typically something that is implemented between
the shadow support code and the generic syscall code, this does not have
to leak anywhere else.

> > - core skin fdtable
> If we can find a minimally invasive first version (see other thread)
> that can be tested and stabilized within very few weeks, and later
> changes will definitely only touch core code, I might be able to live
> with this for 2.5.
> Jan

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