docs: def getEdges(self, fromVol):
          """ Return the edges available from fromVol. """
          if fromVol is None:
              for toVol in self.paths:
                  yield Store.Diff(self, toVol, fromVol, toVol.size)
              return
  
          if fromVol not in self.paths:
              return
  
          fromBVol = self.butterVolumes[fromVol.uuid]
          parentUUID = fromBVol.parent_uuid
          butterDir = os.path.dirname(fromBVol.fullPath)
  
          vols = [vol for vol in self.butterVolumes.values()
                  if vol.parent_uuid == parentUUID or
                  os.path.dirname(vol.fullPath) == butterDir
                  ]
  
          changeRate = self._calcChangeRate(vols)
  
          for toBVol in vols:
              if toBVol == fromBVol:
                  continue
  
              # This gives a conservative estimate of the size of the diff
  
              estimatedSize = self._estimateSize(toBVol, fromBVol, changeRate)
  
              toVol = self._btrfsVol2StoreVol(toBVol)
  
              yield Store.Diff(self, toVol, fromVol, estimatedSize, sizeIsEstimated=True)