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[188.85.150.151]) by smtp.gmail.com with ESMTPSA id v3-20020adfa1c3000000b0032d8354fb43sm14068571wrv.76.2023.10.16.06.28.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Oct 2023 06:28:07 -0700 (PDT) From: Juan Quintela To: Markus Armbruster Cc: qemu-devel@nongnu.org, Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Fam Zheng , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Eric Blake , libvir-list@redhat.com, Fabiano Rosas , qemu-block@nongnu.org, Peter Xu , Leonardo Bras , "Dr. David Alan Gilbert" , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Stefan Hajnoczi , Thomas Huth , Hailiang Zhang , Paolo Bonzini Subject: Re: [PATCH v4 03/10] migration: migrate 'inc' command option is deprecated. In-Reply-To: <87bkcyixwn.fsf@pond.sub.org> (Markus Armbruster's message of "Mon, 16 Oct 2023 11:42:44 +0200") References: <20231013104736.31722-1-quintela@redhat.com> <20231013104736.31722-4-quintela@redhat.com> <8734yehdoc.fsf@pond.sub.org> <87a5sj59ww.fsf@secure.mitica> <87bkcyixwn.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) Date: Mon, 16 Oct 2023 15:28:05 +0200 Message-ID: <87fs2a3dei.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.129.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Markus Armbruster wrote: > Juan Quintela writes: > >> Markus Armbruster wrote: >>> Juan Quintela writes: >> So what I want, I want to remove -i/-b in the next version (9.0?). For >> the other, I want to remove it, but I don't care if the code is around >> in "deprecated" state for another couple of years if there are still >> people that feel that they want it. >> >> This is the reason that I put a pointer for -i/-b to >> @block/@block-incremental. They are "perfect" replacements. >> >> I can put here to use blockdev-mirror + NBD, but the replacement is not >> so direct. >> >> Does this make sense? > > I see where you're coming from. Now let's change perspective for a > minute: what's the purpose of deprecating stuff? > > We normally deprecate with intent to remove. > > We don't remove right away, because we promised to first deprecate for a > grace period, so users can adjust in an orderly manner. The deprecation > serves as signal "you need to adjust". The documentation that comes > with it should help with the adjustment. It's commonly of the form "use > $alternative instead". The alternative is often a direct replacement, > but not always. There could even be no replacement at all. We don't > promise replacements, we promise an orderly process, so users can > adjust. > > Sometimes, we don't have firm plans to remove, but are more like "maybe > remove when gets in the way". We could soften the "you need to adjust" > signal in documentation, but I doubt that's a good idea. Regardless, > the need to help users adjust remains. > > Back to your patches. There are two separate interfaces to block > migration, and both are deprecated at the end of the series: > > 1. Migration parameter @block-incremental & friends > > Not in the way, content to keep around for longer if it helps users. > > The deprecation documentation advises to use block-mirror with NBD > instead. All good. > > 2. QMP migrate parameters @inc and @blk > > Firm intent to remove as soon as the grace period expires, because > it's in the way. > > The deprecation documentation advises to use interface 1 instead. > But that's deprecated, too! > > Insufficiently careful readers will miss that the replacement is > deprecated, and just use it. Risks surprise when the replacement > goes away, too. > > More careful readers will realize that this advises to use something > we elsewhere advise not to use. Contradiction! Confusion ensues. > > On further reflection, these readers might conclude that the > *combined* advice is to use block-mirror with NBD instead. This is > correct. > > So why not tell them? > > Perhaps you'd like to give more nuanced advice, like "you should move > to block-mirror with NBD, but if that's not practical for you, you > should at least move to @block-incremental & friends, which will > likely stick around for longer." That's fine. All I'm asking for is > to not make things more confusing than they need to be :) > > [...] Telling this in deprecated.rst is enough? or you want me to put it also in the error/warn messages and qapi? Later, Juan.