Re: [PATCH V2] memory: flat section iterator

[Peter Xu]

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.

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>

-- 
Peter Xu