On 2/10/2016 7:56 PM, Tamas K Lengyel wrote:
On Wed, Feb 10, 2016 at 10:34 AM, Corneliu ZUZU <cz...@bitdefender.com
<mailto:cz...@bitdefender.com>> wrote:
On 2/10/2016 6:39 PM, Tamas K Lengyel wrote:
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 3a90f47..e46be1b 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -14,6 +14,10 @@ config X86
select HAS_MEM_ACCESS
select HAS_MEM_PAGING
select HAS_MEM_SHARING
+ select HAS_VM_EVENT_WRITE_CTRLREG
You mentioned in the previous revision of this series that
currently you only have plans to implement write_ctrleg and
guest_request events for ARM. I think singlestep and
software_breakpoint should not be moved to common without a clear
plan to have those implemented. Now, if you were to include the
implementation of write_ctrlreg and guest_request in this series
and leave the others in x86 as they are now, I don't think there
would be any reason to have these Kconfig options present at all.
Moving what made sense to be moved to common was a suggestion of
Ian's.
The purpose of this patch is to --avoid-- having to go through
this process again
when an implementation of feature X for architecture A != X86
comes into place.
IMHO what is common should stay in common and I don't see any
issues w/
having them there, only advantages (future implementations of
these features will
be easier).
Maybe Ian can chime in on this.
That's the upside. The downside is that in the interim, while those
features are not implemented, we need to add a bunch of Kconfig
variables to decide under what build they are available.
Technically, you don't need to add anything unless you implement that
feature.
E.g. the ARM Kconfig currently contains no mention of these options,
since they're not implemented there @ all.
And when implemented they're only added once and it's one line "select
HAS_....", it's not like you have to specify a command-line
parameter when building Xen or something like that, so IMO they don't
add considerable complexity.
And after all, these kind of situations (i.e. activating/deactivating
code based on architecture) are why arch-specific Kconfigs exist, right?
Why not use them? :)
If it was moved to common only when the feature is available for all
architectures, we wouldn't need that many ifdefs and the code would be
clearer. So I do see why it would be beneficial having these moved to
common now, but I still rather have it happen when it's necessary and
without the Kconfig settings.
What if a 3rd architecture comes into place, you'd have to move them
back from common to the arch-side and get back to the code duplication
we just got rid of?
And if you then also implement it for the 3rd architecture, you move
them back to common from the arch-side?
It seems uncomfortable having to keep track of all architectures when
wanting to add such a feature implementation for just one of them.
I don't know what & if such plans exist for Xen, but why make that
future process of adding in support for other architectures
unnecessarily complicated,
even if it won't happen soon?
Also, IMO the code is clearer like this:
* you know what parts interest you when implementing parts of these
features/when debugging/when simply looking @ the code
* the #ifdefs make it possible for that code to be put in common => that
makes it *clear* that those code parts are NOT
architecture specific and their implementation can be safely used for
all architectures.
* code duplication is avoided => avoid having to reflect a modification
when it happens in more places than it would be necessary
There are disadvantages, everything has a downside but IMHO they are
minor compared to the alternative.
Ian, any comments on this? :)
Thank you,
Corneliu.
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