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Thu, 21 Aug 2025 06:49:22 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHzwOYTFiw7eSMOsDLCyCYu8cDSM5YP43SovTB3WZUuafH6RNFaYSjcWtaKkUYxJMi8MvMYug== X-Received: by 2002:a05:6214:5017:b0:704:f396:913a with SMTP id 6a1803df08f44-70d88f6bd8emr24391856d6.42.1755784161804; Thu, 21 Aug 2025 06:49:21 -0700 (PDT) Received: from x1.local ([174.89.135.121]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-70ba934cf82sm105123186d6.51.2025.08.21.06.49.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Aug 2025 06:49:21 -0700 (PDT) Date: Thu, 21 Aug 2025 09:49:09 -0400 From: Peter Xu To: Vladimir Sementsov-Ogievskiy Cc: mst@redhat.com, farosas@suse.de, raphael@enfabrica.net, sgarzare@redhat.com, marcandre.lureau@redhat.com, pbonzini@redhat.com, kwolf@redhat.com, hreitz@redhat.com, berrange@redhat.com, eblake@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, steven.sistare@oracle.com, den-plotnikov@yandex-team.ru Subject: Re: [PATCH 27/33] migration/socket: keep fds non-block Message-ID: References: <20250813164856.950363-1-vsementsov@yandex-team.ru> <20250813164856.950363-28-vsementsov@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline 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: -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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Aug 21, 2025 at 03:15:24PM +0300, Vladimir Sementsov-Ogievskiy wrote: > On 20.08.25 16:30, Peter Xu wrote: > > On Wed, Aug 13, 2025 at 07:48:48PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > For migration channel keep fds non-blocking property as is. > > > It's needed for future local migration of fds. > > > > It is pretty risky. This changes the attribute for all the iochannels that > > migration incoming side uses, including multifd / postcopy / ... > > But for now nobody (except CPR-transfer) really pass fds through migration, > and for CPR-transfer it's obviously better to preserve the state by default (see > my answer in previous patch). > > So I think, we are in a point, where we can chose the good default, and > document it. > > > > > I left comment in previous patch as a pure question trying to understand > > whether the feature is needed. If it is, here it might still be good to: > > > > - Above the line add a comment explaning why > > - Only apply it to whatever channel that matters. In this case, IIUC > > only the main channel matters > > > > I still think that preserving non-blocking flag "as is" is good default for migration, > please look at my answer in previous patch. However, in this series I may adopt > to any approach. I also commented in the previous patch, let's see whether we can make it not only the default for migration, but the default for iochannels (hence, any chance to drop the new feature flag completely..). If that won't fly, I think this is fine. In that case, please explicitly mention that it's intentional to change all iochannels that migration uses in the commit message, and we can also add a comment inline explaining why we set this default for all migration channels. Thanks, -- Peter Xu