Re: [Qemu-devel] RFC: handling image options with drive-mirror/drive-backup

[Kevin Wolf]

Am 29.09.2016 um 11:09 hat Fam Zheng geschrieben:
> On Thu, 09/29 09:51, Daniel P. Berrange wrote:
> > On Thu, Sep 29, 2016 at 04:43:25PM +0800, Fam Zheng wrote:
> > > On Thu, 09/29 09:34, Daniel P. Berrange wrote:
> > > > So my suggestion is that we deprecate "drive-mirror" and define a fixed
> > > > command "drive-mirror-blockdev" (or "blockdev-mirror" ?) that accepts
> > > > the proper BlockdevOptions QAPI type for the target as above.
> > > 
> > > Are you aware that there is already a blockdev-mirror command? Supposedly 
> > > it
> > > can do what you need, together with blockdev-add once the latter is deemed
> > > ready.
> > 
> > Clearly I'm not aware of that :-)  It seems libvirt does not yet use
> > blockdev-mirror either, which is where I got the original bug report
> > about drive-mirror from.
> 
> Libvirt doesn't support blockdev-add yet, because the command is still being
> actively worked on at QEMU side, and is therefore thought to be not "stable"
> yet. Though, I think blockdev-add + blockdev-{mirror,backup} are already 
> useful
> for common tasks (like your use case with LUKS).

Just to clarify what "not stable" means: Literally none of the
blockdev-add commands that used to work when it was originally merged
are still working. And we're considering another similar change
(removing the "options" indirection) that will change the command for
all users. So while I would encourage libvirt to write prototyp code for
supporting blockdev-add now, I would advise against enabling it in a
release yet.

> > I'll submit a patch to mark drive-mirror as deprecated and point the
> > otherwise ignorant reader towards blockdev-mirror instead....
> 
> For above reasons, not sure whether we want to advertise it already.
> Anyway deprecating drive-mirror is a bit too early.

That was my first thought, too. However, blockdev-{mirror,backup} can
also work with drives added with -drive or drive_add, so it might be
useful enough even without blockdev-add.

Kevin