Kevin Wolf <kw...@redhat.com> wrote: > Am 14.11.2011 20:49, schrieb Anthony Liguori: >> On 11/14/2011 01:46 PM, Juan Quintela wrote: >>> Anthony Liguori<aligu...@us.ibm.com> wrote: >>>> On 11/14/2011 07:11 AM, Juan Quintela wrote: >>>>> >>>>>> diff --git a/cpus.c b/cpus.c >>>>>> index 82530c4..ae5ec99 100644 >>>>>> --- a/cpus.c >>>>>> +++ b/cpus.c >>>>>> @@ -398,6 +398,7 @@ static void do_vm_stop(RunState state) >>>>>> vm_state_notify(0, state); >>>>>> qemu_aio_flush(); >>>>>> bdrv_flush_all(); >>>>>> + bdrv_invalidate_cache_all(); >>>>>> monitor_protocol_event(QEVENT_STOP, NULL); >>>>>> } >>>>> >>>>> This is too much. Reopening all qcow2 images each time that we stop the >>>>> vm looks excesive, no? >>>> >>>> This general code came in via: >>>> >>>> http://mid.gmane.org/cover.1290613959.git....@redhat.com >>>> >>>> That series made migration stable after issuing a stop operation. I >>>> believe the justification was for debugging purposes or something like >>>> that. >>>> >>>> At any rate, invalidating the cache is part of what's required to make >>>> things stable. If you look at something like cache=unsafe, the only >>>> way the metadata will get flushed if via a bdrv_close since bdrv_flush >>>> is a nop. >>>> >>>> So this is needed as long as we care about supporting this use-case. >>> >>> Then we need a "proper" qcow2 invalidate call. Doing in qemu toplevel: >>> >>> (qemu)stop >>> >>> And now all your qcow2 block devices are closed, or perhaps failing to >>> re-open() looks too much to me (TM). >>> >>> Kevin? >> >> Look closely at the patch. It doesn't actually close()/open() anything.
Sorry, someday I will remember the difference between bdrv_open() and bdrv_file_open(). >> It just invokes the bdrv_close() routine which calls the free functions on >> the >> l1/l2 caching functions. bdrv_open() doesn't actually open anything (it >> assumes >> the file is already open. It just reads the header and metadata over again. >> >> For something that's basically a hack, it turned out to work very cleanly :-) > > But why do we need to do it on stop? > > I don't think it makes even sense logically: bdrv_invalidate_cache() > means "throw all your caches away and refetch everything from disk". > What do we gain from doing this on stop? To some degree I could > understand if you did it on cont, so that you can modify an image on the > host while the VM is stopped (though I would still consider it criminal > :-)). Fully agree. When I answered, I was thinking that I "could" want it on "cont", just to be able to do evil things. But I thought it was "criminal" just to write the idea O:-) Later, Juan.
