Re: [Qemu-block] [PATCH for-2.11] qcow2: fix image corruption on commit with persistent snapshot

[Kevin Wolf]

Am 17.11.2017 um 18:07 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 17.11.2017 19:47, Eric Blake wrote:
> > If an image contains persistent snapshots, we cannot use the
> 
> bitmaps
> 
> > fast path of bdrv_make_empty() to clear the image during
> > qemu-img commit, because that will lose the clusters related
> > to the bitmaps.
> > 
> > Also leave a comment in qcow2_read_extensions to remind future
> > feature additions to think about fast-path removal, since we
> > just barely fixed the same bug for LUKS encryption.
> > 
> > It's a pain that qemu-img has not yet been taught to manipulate,
> > or even at a very minimum display, information about persistent
> > bitmaps; instead, we have to use QMP commands.  It's also a
> > pain that only qeury-block and x-debug-block-dirty-bitmap-sha256
> > will allow bitmap introspection; but the former requires the
> > node to be hooked to a block device, and the latter is experimental.
> 
> sorry for that pain =(.
> 
> Honestly, I don't understand why such a simple and obvious fix needs an
> additional test.

Because we could otherwise accidentally break it again in the future.

If there is a feature that you care about, make sure to have a test for
everything in it, and that you add a regression test for every bug that
you fix.

Kevin