Re: [PATCH 1/2] qcow2: Release read-only bitmaps when inactivated

[Peter Krempa]

On Thu, Jul 30, 2020 at 14:02:33 +0200, Max Reitz wrote:
> During migration, we release all bitmaps after storing them on disk, as
> long as they are (1) stored on disk, (2) not read-only, and (3)
> consistent.
> 
> (2) seems arbitrary, though.  The reason we do not release them is
> because we do not write them, as there is no need to; and then we just
> forget about all bitmaps that we have not written to the file.  However,
> read-only persistent bitmaps are still in the file and in sync with
> their in-memory representation, so we may as well release them just like
> any R/W bitmap that we have updated.
> 
> It leads to actual problems, too: After migration, letting the source
> continue may result in an error if there were any bitmaps on read-only
> nodes (such as backing images), because those have not been released by
> bdrv_inactive_all(), but bdrv_invalidate_cache_all() attempts to reload
> them (which fails, because they are still present in memory).
> 

I've tested it with same commands as I've used before and now the 'cont'
succeeds and also the bitmaps after the cont call are loaded and active
at least according to 'query-named-block-nodes'

Tested-by: Peter Krempa <pkrempa@redhat.com>