Re: [PATCH V2] memory: flat section iterator

[Steven Sistare]

On 2/7/2023 4:47 PM, Peter Xu wrote:
> On Tue, Feb 07, 2023 at 04:28:49PM -0500, Steven Sistare wrote:
>> On 2/7/2023 3:10 PM, Peter Xu wrote:
>>> On Tue, Feb 07, 2023 at 11:03:29AM -0800, Steve Sistare wrote:
>>>> Add an iterator over the sections of a flattened address space.
>>>> This will be needed by cpr to issue vfio ioctl's on the same memory
>>>> ranges that are already programmed.
>>>
>>> Should this better be proposed with the context of using it?  Or I don't
>>> know how to justify this new interface is needed.
>>>
>>> For example, any explanations on why memory region listeners cannot work?
>>
>> For context, the new interfaces is used in the patch
>>   "vfio-pci: recover from unmap-all-vaddr failure"
>> in the original live update series:
>>   
>> https://lore.kernel.org/qemu-devel/1658851843-236870-1-git-send-email-steven.sistare@oracle.com/
>>
>> More succinctly, the memory region listeners already ran, and the vfio 
>> callbacks created vfio memory regions.  Now we want to perform live update,
>> and are in steady state, so no listeners are being called.  We need the
>> flat section iterator to reproduce the same addresses and extents that were
>> produced by the listeners, to make a state change on each distinct vfio
>> memory region.
> 
> Okay it makes sense, thanks.
> 
> I think it'll be the same as one memory_listener_register() followed by an
> unregister with region_add() hooked only, but maybe we should avoid
> fiddling with the global list of listeners when possible.

Indeed it is the same, thanks for the suggestion.  And this occurs infrequently,
so modifying the listener list has no impact.  

I withdraw this patch request.  Thank you all for reviewing it.

- Steve

> If you plan to keep posting it separately, would you add some information
> into the commit message?  With that enhanced, please feel free to add:
> 
> Acked-by: Peter Xu <peterx@redhat.com>
>