* Alexander Graf (ag...@suse.de) wrote: > > > On 13.02.15 10:04, Dr. David Alan Gilbert wrote: > > * Alexander Graf (ag...@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 <ag...@suse.de <mailto:ag...@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 <ag...@suse.de <mailto:ag...@suse.de>> > >>> Signed-off-by: Amit Shah <amit.s...@redhat.com > >>> <mailto:amit.s...@redhat.com>> > >>> Signed-off-by: Juan Quintela <quint...@redhat.com > >>> <mailto:quint...@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.
Yes, that's fair. My suspicion (for which I have no proof) is that it might depend on the amount of buffer in the connection; if there's enough buffer to hold your JSON description it'll work, because you'll have sent the JSON before the destination has spotted the terminator; if you've not got much buffering (e.g. on a local fd) then the source might get stuck trying to write the json or error because the destination has closed the fd. Dave > > > Alex -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK