Hi, When beginning migration, the qcow2 driver syncs all persistent bitmaps to disk and then releases them. If the user decides to continue on the source after migration, those bitmaps are re-loaded from the qcow2 image.
However, we only do this for bitmaps that were actively synced, i.e. R/W bitmaps. RO bitmaps (those on backing images) are not written and thus not released. However, we still try to re-load them when continuing, and that will then fail. To fix this problem, I think we should just consider RO bitmaps to be in sync from the beginning, so we can release them just like bitmaps that we have actively written back to the image. This is done by patch 1. However, there’s a catch: Peter Krempa noted that it isn’t in libvirt’s interest for the bitmaps to be released before migration at all, because this makes them disappear from query-named-block-node’s dirty-bitmaps list, but libvirt needs the bitmaps to be there: https://bugzilla.redhat.com/show_bug.cgi?id=1858739#c3 If it’s really not feasible to keep the bitmaps around, then I suppose what might work for libvirt is to query image/format-specific/data/bitmaps in addition to dirty-bitmaps (every bitmap that we released before migration must be a persistent bitmap). What are your thoughts on this? Max Reitz (2): qcow2: Release read-only bitmaps when inactivated iotests/169: Test source cont with backing bmap block/qcow2-bitmap.c | 23 +++++++++++--- tests/qemu-iotests/169 | 64 +++++++++++++++++++++++++++++++++++++- tests/qemu-iotests/169.out | 4 +-- 3 files changed, 84 insertions(+), 7 deletions(-) -- 2.26.2
