On 11/03/2016 05:47 PM, Jianjun Duan wrote: > > On 11/03/2016 05:22 AM, Halil Pasic wrote: >> > >> > >> > On 11/02/2016 11:47 AM, Juan Quintela wrote: >>> >> Jianjun Duan <du...@linux.vnet.ibm.com> wrote: >>>> >>> Add a test for QTAILQ migration to tests/test-vmstate.c. >>>> >>> >>>> >>> Signed-off-by: Jianjun Duan <du...@linux.vnet.ibm.com> >>> >> >>> >> Reviewed-by: Juan Quintela <quint...@redhat.com> >>> >> >> > >> > Empty QTAILQ seems to be broken. Have written a small >> > test to prove my point. It May even make sense to have such >> > a test in the test-suite (some prettyfication might be >> > necessary though). >> > > It is working as intended. >
My train of thought was that the object holding the queue might be dynamically allocated by the migration code or otherwise uninitialized. I was unaware these scenarios are prohibited. > The current design is to append the qtailq from source to the > corresponding one on target. I do not see this documented. I'm used to vmstate_load overwriting values and following pointers, so IMHO it is not obvious that qtailq load does append. > It works well for the task in hard > such as migrating ccs_list and pending_events for DRC objects. > Because target head is always properly initialized to empty queue? > I suspect in most cases the qtailqs on target are empty. If I think about migration having no queues populated with elements on a target site sounds very reasonable since IFAIU the target should not do any work which would populate these data structures. > If not, > appending to them is a good choice. Clearing them is tricky since > each queue probably require a specialized routine to clean. If they > are not empty there are must be good reasons for that. Have you some code or a scenario in mind where this is legit? I mean creating a mix of the state(?) we found at the target and the state captured at the source does not sound right. I would argue that the target should not have any state which is subject to migration. You are right a non-empty queue is trouble, and frankly I never considered it as a valid scenario. Sorry if I'm bothering you with nonsense. Greetings, Halil > > Thanks, > Jianjun >
