Re: [Qemu-devel] HEAD is failing virt-test on migration tests

[Alexander Graf <agraf@suse.de>]

On 13.02.15 10:04, Dr. David Alan Gilbert wrote:
> * Alexander Graf (agraf@suse.de) wrote:
>>
>>
>> On 13.02.15 01:29, Lucas Meneghel Rodrigues wrote:
>>> Copying Alex.
>>>
>>> OK, after bisecting, this is what I've got:
>>>
>>> 8118f0950fc77cce7873002a5021172dd6e040b5 is the first bad commit
>>> commit 8118f0950fc77cce7873002a5021172dd6e040b5
>>> Author: Alexander Graf <agraf@suse.de <mailto:agraf@suse.de>>
>>> Date:   Thu Jan 22 15:01:39 2015 +0100
>>>
>>>     migration: Append JSON description of migration stream
>>>     
>>>     One of the annoyances of the current migration format is the fact that
>>>     it's not self-describing. In fact, it's not properly describing at all.
>>>     Some code randomly scattered throughout QEMU elaborates roughly how to
>>>     read and write a stream of bytes.
>>>     
>>>     We discussed an idea during KVM Forum 2013 to add a JSON description of
>>>     the migration protocol itself to the migration stream. This patch
>>>     adds a section after the VM_END migration end marker that contains
>>>     description data on what the device sections of the stream are
>>> composed of.
>>>     
>>>     This approach is backwards compatible with any QEMU version reading the
>>>     stream, because QEMU just stops reading after the VM_END marker and
>>> ignores
>>>     any data following it.
>>>     
>>>     With an additional external program this allows us to decipher the
>>>     contents of any migration stream and hopefully make migration bugs
>>> easier
>>>     to track down.
>>>     
>>>     Signed-off-by: Alexander Graf <agraf@suse.de <mailto:agraf@suse.de>>
>>>     Signed-off-by: Amit Shah <amit.shah@redhat.com
>>> <mailto:amit.shah@redhat.com>>
>>>     Signed-off-by: Juan Quintela <quintela@redhat.com
>>> <mailto:quintela@redhat.com>>
>>>
>>> :040000 040000 e9a8888ac242a61fbd05bbb0daa3e8877970e738
>>> 61df81f831bc86b29f65883523ea95abb36f1ec5 Mhw
>>> :040000 040000 fe0659bed17d86c43657c26622d64fd44a1af037
>>> 7092a6b6515a3d0077f68ff2d80dbd74597a244f Minclude
>>> :040000 040000 d90d6f1fe839abf21a45eaba5829d5a6a22abeb1
>>> c2b1dcda197d96657458d699c185e39ae45f3c6c Mmigration
>>> :100644 100644 98895fee81edfbc659fc42d467e930d06b1afa7d
>>> 80407662ad3ed860d33a9d35f5c44b1d19c4612b Msavevm.c
>>> :040000 040000 cf218bc2b841cd51ebe3972635be2cfbb1de9dfa
>>> 7aaf3d10ef7f73413b228e854fe6f04317151e46 Mtests
>>>
>>> So there you go. I'm going to sleep, if you need any extra help let me know.
>>
>> So the major difference with this patch applied is that the sender could
>> send more data than the receive wants to read. I can't see the actual
>> migrate command you used down there.
>>
>> I haven't seen this actually being a problem so far, as the receiver
>> just close()s its file descriptor once it hits VM_EOF. This should only
>> break senders if they expect they can send more. That said, I think I
>> only tested offline migration (via exec:), so maybe QEMU is behaving
>> badly and actually wants to send all data and just fails the migration
>> without?
> 
> Hmm, for such an odd change to the migration stream it's a surprise you
> didn't test it live.

Well, let's say I don't remember explicitly testing it live - I probably
did at one point.

I just verified that migrating with tcp:... works fine in master.


Alex