Thank you for the clarification. On Wed, Nov 16, 2022 at 5:11 PM Peter Krempa <pkre...@redhat.com> wrote:
> On Wed, Nov 16, 2022 at 09:17:43 +0800, Jiatong Shen wrote: > > Hello Community, > > > > We are observing that after a blockcopy, the disk backend will inherit > > from original disk's cache mode configuration even though a new cache > mode > > is given. Specifically, the function > > > https://github.com/libvirt/libvirt/blob/cd94d891fb4b5cdda229f58b1dee261d5514082b/src/qemu/qemu_domain.c#L10887 > > which eventually calls qemuDomainPrepareDiskSourceData and override > input > > config. > > My question is is this on purpose? Because seems like qemu allows > different > > configs. > > Thnak you very much for the help. > > This is an historical artifact from the time when the block copy API > used the 'drive-mirror' QMP API of qemu which didn't allow configuring > any image specific parameters. > > Nowadays we use 'blockdev-mirror' which takes an image instantiated via > 'blockdev-add' which can configure everything the same way as the disk, > so it would be possible to honour the cache mode as specified in the > block copy XML. > > Note that if you intend to implement it, the code must still preserve > the original cache mode if the user doesn't specify it in the XML. > > -- Best Regards, Jiatong Shen
