Re: [libvirt] [PATCH 2/4] backup: Add two new qemu capabilities

On 6/6/19 7:51 AM, Peter Krempa wrote: > On Wed, Jun 05, 2019 at 22:01:08 -0500, Eric Blake wrote: >> Add two capabilities for testing features required for the upcoming >> virDomainBackupBegin: use block-dirty-bitmap-merge as the generic >> witness of bitmap support needed for checkpoints (since all of the >> bitmap management functionalities were finalized in the same qemu 4.0 >> release), and the bitmap parameter to nbd-server-add for pull-mode >> backup support. Even though both capabilities are likely to be >> present or absent together (that is, it is unlikely to encounter a >> qemu that backports only one of the two), it still makes sense to keep >> two capabilities as the two uses are orthogonal (full backups don't >> require checkpoints, push mode backups don't require NBD bitmap >> support, and checkpoints can be used for more than just incremental >> backups). >> >> Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; >> --- >> src/qemu/qemu_capabilities.h | 4 ++++ >> src/qemu/qemu_capabilities.c | 6 ++++++ >> tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml | 2 ++ >> tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml | 2 ++ >> tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml | 2 ++ >> tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml | 2 ++ >> tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml | 2 ++ >> tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml | 2 ++ >> 8 files changed, 22 insertions(+) > > So the code looks good to me, but we need to clarify one thing before > ACK. > > Is there anything that would change libvirt's behaviour incompatibly if > these are specified? In some cases these also imply a libvirt behaviour > change (e.g. different command line) and thus not pushing those in the > same release as the implementation might cause problems. So far, the only things that depend on the capabilities are the new code additions for checkpoints and pull-mode backups; existing libvirt.git should have no change in behavior whether or not the capabilities are detected.