On 01/09/2013 02:12:16 PM, Alexander Graf wrote:
On 09.01.2013, at 20:50, Scott Wood wrote:
> On 01/09/2013 10:48:47 AM, Alexander Graf wrote:
>> On 09.01.2013, at 17:26, Christoffer Dall wrote:
>> > Renames the KVM_SET_DEVICE_ADDRESS to KVM_ARM_SET_DEVICE_ADDR
>> > to make it obvious that this is ARM specific in lack of a better
generic
>> > interface.
>> >
>> > Once we agree on a better interface the KVM/ARM code can also
take
>> > advantage of that, but until then we don't want to hold up the
KVM/ARM
>> > patches.
>> Works for me. Scott, are you happy with this one too?
>
> Not really, given that it will stay around forever even after
something new is introduced.
But only in ARM specific code.
...which I'll probably have to deal with when Freescale's
virtualization-capable ARM chips come along. I don't see "it's only in
that other architecture" as "it might as well not exist".
> If you're going to change the name, why not just change it to
KVM_SET_DEVICE_CONFIG? Can we change the name later if nothing else
changes (so it's still binary compatible)?
Because that again implies that it's generic enough. And to reach
that conclusion will take more time than we should spend on this now.
If the conclusion later on is that it is good enough, can the name be
changed then?
>> We can start to introduce (and fix ARM) with a generic ioctl in
the MPIC patches then.
>
> The ioctl is already generic, except for its name.
It's making a few wrong assumptions:
* maximum size of value is u64
This is tolerable IMHO.
* combining device id (variable) with addr type id (const) into a
single field. It could just be split into multiple fields
I agree, but that could be lived with as well.
I get that there's a tradeoff between getting something in now, versus
waiting until the API is more refined. Tagging it with a particular
ISA seems like an odd way of saying "soon to be deprecated", though.
What happens if we're still squabbling over the perfect replacement API
when we're trying to push PPC MPIC stuff in?
Perhaps the threshold for an API becoming "permanent" should not be
acceptance into the tree, but rather the removal of an "experimental"
tag (including a way of shutting off experimental APIs to make sure
you're not depending on them). Sort of like CONFIG_EXPERIMENTAL,
except actually used for its intended purpose (distributions should
have it *off* by default), and preferably managed at runtime. Sort of
like drivers/staging, except for APIs rather than drivers. Changes at
that point should require more justification than before merging, but
would not have the strict compatibility requirement that
non-experimental APIs have. This would make collaboration and testing
easier on APIs that aren't ready to be permanent.
* the id is 100% architecture specific. It shouldn't be. At least
the "device id" field should be generic.
That's a documentation issue that could be changed to have all
architectures adopt what is currently specified for ARM, without
breaking compatibility.
I'm not sure if we can come up with more problems in that API when
staring at it a bit longer and/or we would actually start using it
for more things. So for the sake of not holding up the ARM code, I'm
perfectly fine to clutter ARM's ioctl handling code with an ioctl
that is already deprecated at its introduction, as long as we don't
hold everything else up meanwhile.
I'm not in a position to block it, and if I were I presumably would
have seen this in time for feedback to matter. That's different from
actually being happy. :-)
-Scott
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