Re: [PATCH] migration: Fix writing mapped_ram + ignore_shared snapshots

[Peter Xu <peterx@redhat.com>]

On Thu, Nov 27, 2025 at 11:35:06AM +0000, Paweł Zmarzły wrote:
> On Wed, 26 Nov 2025 at 21:42, Peter Xu <peterx@redhat.com> wrote:
> > Now I start to question whether I should have that other fix of yours to be
> > for this release or next.
> >
> > If this use case is completely broken, we shouldn't need to rush -rc
> > window, now I plan to merge all these fixes later when 11.0 dev window
> > opens.  Let me know if you, or Fabiano, has any comments.
> 
> It is broken if you set ignore-shared and actually have any shared
> block, but what could work today is if you just toggle the
> ignore-shared flag on without setting up any shared blocks. In that
> case, writing will work fine, but reading will crash. That's how I

Yep, I suppose either side of reliable failure means it's completely
broken. :(

That's IMHO an important evaluation because we could modify the image
layout without worrying breaking others only if it's completely broken..

> stumbled upon this rabbithole in the first place: I forgot to unset
> the flag and was surprised by parsing error. Whether it is worth
> fixing now - I don't know, setting ignore-shared when there are no
> shared blocks doesn't really make sense, so most likely nobody does it
> on purpose.
> 
> In either case, I need to stop working on this for now, I thought this
> will be a tiny side project that'll help me get my first patches in
> (and get used to collaborating over email), but now it's growing in
> complexity and I have other things that I need to prioritize.
> Hopefully I'll come back to this within 11.x window. Thanks for all
> the help so far, Peter, Fabiano!

Don't worry, thanks for all the contributions even so far!

Your patch actually looks pretty good already and mergeable, I just
nitpicked things here and there as I want to double check on things I
stated, and make it slow to get thoroughly discussed.

Personally, I think it's ok we queue this one already into -next together
with the other one, then we clean things on top.

Fabiano, sounds good to you?  PS: take your time reading, as long as you
agree we put it in -next only, then there's no rush. :)

Thanks,

-- 
Peter Xu