fix: do not make base copy RO for QCOW2 (#162)

If we make the base copy RO, the next live coalesce could fail on the call to
tapdisk commit since the chain is only made RW at the activation.

Signed-off-by: Damien Thenot <damien.thenot@vates.tech>

Author: Nambrok

drivers/LVMSR.py

@@ -1864,8 +1864,12 @@ def _snapshot(self, snapType, cloneOp=False, cbtlog=None, cbt_consistency=None,
             util.fistpoint.activate("LVHDRT_clone_vdi_after_parent_hidden", self.sr.uuid)
 
             # set the base copy to ReadOnly
-            self.sr.lvmCache.setReadonly(self.lvname, True)
-            util.fistpoint.activate("LVHDRT_clone_vdi_after_parent_ro", self.sr.uuid)
+            if not self.cowutil.isCoalesceableOnRemote():
+                # For QCOW2, the whole chain need to be
+                # writable for tapdisk to do the coalesce.
+                # In this case, we don't mark the base copy RO.
+                self.sr.lvmCache.setReadonly(self.lvname, True)
+                util.fistpoint.activate("LVHDRT_clone_vdi_after_parent_ro", self.sr.uuid)
 
             if hostRefs:
                 self.sr._updateSlavesOnClone(hostRefs, origOldLV,