Re: [MirageOS-devel] Mirage on Xen/ARM status

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 23 Jun 2014, at 09:02, Thomas Leonard <talex5@xxxxxxxxx> wrote:

> On 4 June 2014 13:33, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>> An update on the Mirage/ARM port:
> [...]
>> My current plan is:
>> 
>> - Upstream Karim's initial ARM support to Xen. I split the original
>> patch into three smaller ones and submitted them, but they want it
>> broken up further, which is fair enough.
> 
> We're going through many of rounds of review with these patches (no
> major problems - mainly style issues). I'm going to split them up
> further to make them easier to review.

Thanks for going through the upstreaming so patiently; it's very good
to know that we're reducing our custom-fork technical debt.

>> - Upstream my patches to build a libminios.a library, plus some other
>> fixes to the build system.
> 
> The fixes to the build system have been accepted, but the library
> patches are waiting for the ARM patches to go in first (otherwise
> we'll get conflicts).

>> - Make some changes to Mini-OS to work unmodified with Mirage
>> (specifically: expose grant table details, disable interrupt-based
>> event handlers, and allow linking only the features we need).
> 
> These are also waiting on the previous patches (and need tidying up).
> 
> We'll need to make our own release of Mini-OS at some point for Mirage
> 2.0, and almost certainly before these patches are accepted upstream.
> 
> The later we do it, the closer it will be to what eventually ends up
> upstream in Xen. The sooner, the more time we have for testing against
> it. Does some time this week sound reasonable?

Some time this week sounds great.  Since we now know with reasonable
certainty that the libminios.a will exist upstream, running with our
forked version is fine for a while (and possibly forever, if minor local
patches are needed, or we want to do something like tidy up the console
logging in such a way that upstream doesn't like it).

> 
>> - Add a proper string library to mirage-platform to replace Mini-OS's
>> limited sprintf.
> 
> I'll probably add the FreeBSD one here.

Ack.

> 
>> - Upstream my patches to mirage-platform and mirage to build using the
>> new libminios and openlibm (these are on github in my forks).
> 
> How do we want to do this? Can we just tell everyone to upgrade mirage
> and mirage-platform together, and get Mini-OS and openlibm at the same
> time, or should we add backwards-compatibility hacks so e.g. mirage
> can configure for either the old or new version of mirage-platform?

Mirage 1.2.0 will be the last of the 1.x series (except any minor bugfix
releases), and out this week.

After that, we can merge the 2.0 branch into trunk, which can include the
Makefile changes needed for the new MiniOS (as well as V2 mirage-types).

There's no need for backwards compatibility hacks between Mirage 1.x and
2.x.  The one hitch is that it's not possible to specify a version
constraint on the command line (e.g. so that `opam install mirage-xen {<2.0}`
will work), so releasing a new mirage-platform will result in older
setups breaking if they upgrade.  I'm not sure there's much we can do
about that beyond instruct users of old Mirage to pin packages, or
pick a new name such as mirage-platform-xen.  Both are confusing :(

> 
>> - Upstream my Mini-OS ARM patches to Xen.
> 
> I squashed these into Karim's ARM patches to simplify the review (no
> point reviewing code that's about to be replaced).
> 
>> - Add a start_info structure on ARM, or find some other way to expose
>> those details to Mirage.
> 
> This is done, and simplified things greatly. No changes are now needed
> in mirage-console, etc for ARM.
> 
> We also need to sort out the ones complement stuff for networking on
> ARM, but that can come after the upgrade to the new Mini-OS (which is
> the big change; once we have that, ARM support comes almost for free).

Agreed!

-anil

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