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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-4db797d43dcsm998001173.37.2024.10.07.11.12.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Oct 2024 11:12:05 -0700 (PDT) Date: Mon, 7 Oct 2024 14:12:03 -0400 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Steve Sistare , qemu-devel@nongnu.org, Fabiano Rosas , David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , Markus Armbruster Subject: Re: [PATCH V2 07/13] migration: SCM_RIGHTS for QEMUFile Message-ID: References: <1727725244-105198-1-git-send-email-steven.sistare@oracle.com> <1727725244-105198-8-git-send-email-steven.sistare@oracle.com> 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=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.153, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Oct 07, 2024 at 05:35:37PM +0100, Daniel P. Berrangé wrote: > See 'man 7 unix': > > [quote] > At least one byte of real data should be sent when > sending ancillary data. On Linux, this is required to > successfully send ancillary data over a UNIX domain > stream socket. When sending ancillary data over a > UNIX domain datagram socket, it is not necessary on > Linux to send any accompanying real data. However, > portable applications should also include at least one > byte of real data when sending ancillary data over a > datagram socket. > [/quote] > > So if your protocol doesn't already have a convenient bit of real data to > attach the SCM_RIGHTS data to, it is common practice to send a single dummy > data byte that is discarded. Ah OK, thanks. Then maybe we can still consider dropping the initial four bytes for fd migrations; I left the other comment in the next patch. -- Peter Xu