Re: [Qemu-block] [Qemu-devel] [PATCH 4/6] dirty-bitmaps: clean-up bitmaps loading and migration logic

[Vladimir Sementsov-Ogievskiy]

17.09.2018 21:33, John Snow wrote:
> On 09/17/2018 11:51 AM, Vladimir Sementsov-Ogievskiy wrote:
> > Hmm, ping, anybody here ?)
> Was preparing to stage on Friday, working on it now.
>
> I never understood why you forbid the transfer of read only bitmaps
> though, can you point that out for me?
>
> --js

readonly bitmap - means it is not marked in_use in qcow2 file.

Hm, I don't remember exact reason, but at least for shared migration it 
is unsafe to migrate readonly bitmap without special handling: we 
migrate it, it becomes not-readonly, it changes in RAM, then (assume) 
storing failed and we have old version ofthe bitmap in qcow2, which is 
not marked in_use.. So it should be somehow carefully handled, the 
simplest option is just to forbid it.

--
Best regards,
Vladimir