The copy-on-read drive must not request the WRITE_UNCHANGED permission
for its child if the node is inactive, otherwise starting a migration
destination with -incoming will fail because the child cannot provide
write access yet:
qemu-system-x86_64: -blockdev copy-on-read,file=img,node-name=cor: Block node is read-only
Earlier QEMU versions additionally ran into an abort() on the migration
source side: bdrv_inactivate_recurse() failed to update permissions.
This is silently ignored today because it was only supposed to loosen
restrictions. This is the symptom that was originally reported here:
https://bugzilla.redhat.com/show_bug.cgi?id=1733022
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
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