fix: do not make base copy RO for QCOW2

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,