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Tsirkin" , Markus Armbruster , Eric Blake , "Maciej S. Szmigiero" , Jason Wang , Ben Chaney , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH RFC 0/2] migration/vl: new -incoming config:* for early migration parameters Message-ID: References: <20260528212947.368132-1-peterx@redhat.com> <87se7btcq9.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jun 03, 2026 at 10:48:54AM +0100, Daniel P. Berrangé wrote: > On Fri, May 29, 2026 at 10:15:35AM -0400, Peter Xu wrote: > > On Thu, May 28, 2026 at 07:01:50PM -0300, Fabiano Rosas wrote: > > > Peter Xu writes: > > > > > > > CI: https://gitlab.com/peterx/qemu/-/pipelines/2560168907 > > > > > > > > This series introduces a generic way to specify migration parameters that > > > > can be used even during the early boot phase of QEMU. > > > > > > > > One example use case that already existed is CPR-transfer / CPR-exec. > > > > currently QEMU has a temporary global variable (incoming_mode) to achieve > > > > this, but it's hard to understand and this hack bleeded into quite a few > > > > places that we could have avoided. The lines in patch 2 touched may > > > > provide some idea. > > > > > > > > With a generic approach of setting migration parameters with cmdlines, we > > > > can remove this hack meanwhile QEMU should be able to keep the CPR behavior > > > > as before. To CPR maintainers and reviewers: please have a closer look, > > > > even better if it can be smoke tested, to see if this works for Oracle's > > > > environment, TIA. > > > > > > > > The 1st patch implemented that new semantics. It is straightforward: now > > > > we can setup any migration parameter using an extra line of: > > > > > > > > -incoming config:key1=value1,key2=value2,... > > > > > > Just merge my code mate. > > > https://lore.kernel.org/r/20251215220041.12657-25-farosas@suse.de > > > > Heh, I apologize. I totally forgot it even if I seem to have read it.. > > > > The goal is differnent, though, which is to make it available before > > migration object initialization. Say, I wished -global would work too but > > it doesn't, and it just can't. So it's not "something good to have" > > anymore, but functionally required for either CPR and TAP in the future if > > we adopt this, they'll all read them early. > > > > > > > > A couple of differences from my patch: > > > > > > - old-style keyval vs. json; > > > > > > Isn't json preferred nowadays? > > > > I didn't mention it in doc, but yeah this series also supports JSON due to > > the same qapi helper used. I don't suggest json though for this entry (and > > that's also why I didn't mention it..) because 99% of migration parameters > > are scalars and I don't see why we should use JSON here.. the only one not > > scalar is block-bitmap-mapping but it's not intended to be used in > > -incoming at all (even if it'll work..). > > 99% of **todays** parameters are scalars. > > The reason we are actively moving to CLI args which are modelled with QAPI > and expressable using JSON is because that future proofs the command line > for any kind of parameters we might need. > > We should actively document and promote the use of JSON. Ah OK, sure, will do when respin. > > > > - using "config:" > > > > > > This makes it non-uniform with uri and channels which don't have a > > > keyword in front of them. I guess I could live with it, but it seems > > > odd. I see that it makes parsing way easier. > > > > Yeah, having some identifier would be nice. I wished channels also have > > identifiers if we don't need to keep compatibility. > > IMHO having a magic "config:" prefix is an anti-pattern because it > involves custom command line parsing logic. Yes, it's not elegant. I wished we had something like this though when introducing the cpr channels; right now anything wasn't "defer" or URI implies it's a "channel".. I also wanted to avoid introducing new cmdline parameters, so migration incoming cmdlines can stick with the same option. If there's better suggestion please shoot. > > Does "-incoming config" imply '-incoming defer' semantics or is it > independent ? They're independent. Examples: a) "-incoming config:* -incoming tcp:*", setup parameters for TCP incoming migration without further deferral b) "-incoming config:*" only, setup global parameters for a possible upcoming outgoing migration Thanks, -- Peter Xu