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([2a02:8071:5055:3f20:7ad9:a400:6d51:83e6]) by smtp.gmail.com with ESMTPSA id gs35sm1330486ejc.208.2022.02.24.05.05.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Feb 2022 05:05:16 -0800 (PST) Message-ID: <4170577f-bd93-49f3-0f80-7fa41a6cfabc@redhat.com> Date: Thu, 24 Feb 2022 14:05:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v4 17/18] qapi: backup: add immutable-source parameter To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20220216194617.126484-1-vsementsov@virtuozzo.com> <20220216194617.126484-18-vsementsov@virtuozzo.com> From: Hanna Reitz In-Reply-To: <20220216194617.126484-18-vsementsov@virtuozzo.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=hreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Cc: fam@euphon.net, kwolf@redhat.com, wencongyang2@huawei.com, xiechanglong.d@gmail.com, qemu-devel@nongnu.org, armbru@redhat.com, jsnow@redhat.com, nikita.lapshin@virtuozzo.com, stefanha@redhat.com, eblake@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 16.02.22 20:46, Vladimir Sementsov-Ogievskiy wrote: > We are on the way to implement internal-backup with fleecing scheme, > which includes backup job copying from fleecing block driver node > (which is target of copy-before-write filter) to final target of > backup. This job doesn't need own filter, as fleecing block driver node > is a kind of snapshot, it's immutable from reader point of view. > > Let's add a parameter for backup to not insert filter but instead > unshare writes on source. This way backup job becomes a simple copying > process. > > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > qapi/block-core.json | 11 ++++++- > include/block/block_int.h | 1 + > block/backup.c | 61 +++++++++++++++++++++++++++++++++++---- > block/replication.c | 2 +- > blockdev.c | 1 + > 5 files changed, 69 insertions(+), 7 deletions(-) I’m not really technically opposed to this, but I wonder what the actual benefit of this is.  It sounds like the only benefit is that we don’t need a filter driver, but what’s the problem with such a filter driver? (And if we just want to copy data off of a immutable node, I personally would go for the mirror job instead, but it isn’t like I could give good technical reasons for that personal bias.)