Re: [Qemu-devel] [PATCH] Fix -snapshot deleting images on disk change

[Markus Armbruster]

Blue Swirl <address@hidden> writes:

> Block device change command did not copy BDRV_O_SNAPSHOT flag. Thus
> the new image did not have this flag and the file got deleted during
> opening.
>
> Fix by copying BDRV_O_SNAPSHOT flag.

Aha: the file gets deleted because bs->is_temporary survives change, but
BDRV_O_SNAPSHOT does not.  Thus, the new image gets opened without a
snapshot file wrapped around it.  But since is_temporary is still true,
we attempt to delete the (nonexistant) snapshot file, and end up
deleting the image file instead.

Your fix makes sense.  But I recommend to additionally set
bs->is_temporary unconditionally in bdrv_open().  Or get rid of it and
test bs->open_flags instead.