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Mon, 29 Nov 2021 20:49:34 +0000 Message-ID: <671e28a1-b7cf-d0a5-ff7f-c8f0d323d0a8@virtuozzo.com> Date: Mon, 29 Nov 2021 23:49:33 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [RFC for-6.2] block/nbd: forbid incompatible change of server options on reconnect Content-Language: en-US To: Eric Blake Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, hreitz@redhat.com, kwolf@redhat.com References: <20211124140951.439684-1-vsementsov@virtuozzo.com> <20211129191606.4cnbnjpsoywgxeq7@redhat.com> From: Vladimir Sementsov-Ogievskiy In-Reply-To: <20211129191606.4cnbnjpsoywgxeq7@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AM6PR10CA0014.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:209:89::27) To AM9PR08MB6737.eurprd08.prod.outlook.com (2603:10a6:20b:304::18) MIME-Version: 1.0 Received: from [192.168.100.10] (185.215.60.234) by AM6PR10CA0014.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:209:89::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4734.21 via Frontend Transport; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR05-DB8-obe.outbound.protection.outlook.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-1.317, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: 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" 29.11.2021 22:16, Eric Blake wrote: > On Wed, Nov 24, 2021 at 03:09:51PM +0100, Vladimir Sementsov-Ogievskiy wrote: >> Reconnect feature was never prepared to handle server options changed >> on reconnect. Let's be stricter and check what exactly is changed. If >> server capabilities just got richer don't worry. Otherwise fail and >> drop the established connection. >> >> Signed-off-by: Vladimir Sementsov-Ogievskiy >> --- >> + /* >> + * No worry if rotational status changed. But other flags are feature flags, >> + * they should not degrade. >> + */ >> + dropped_flags = (old->flags & ~new->flags) & ~NBD_FLAG_ROTATIONAL; >> + if (dropped_flags) { >> + error_setg(errp, "Server options degrade after reconnect: flags 0x%" >> + PRIx32 " are not reported anymore", dropped_flags); >> + return false; >> + } > > Your logic is good for most flags, but somewhat wrong for > NBD_FLAG_READ_ONLY_BIT. For cases where we are only using the block > device read-only, we don't care about changes of that bit, in either > direction. But for cases where we want to use the block device > read-write, the bit changing from clear in the old to set in the new > server is an incompatible change that your logic failed to flag. > Oh right! Will fix it and resend soon. -- Best regards, Vladimir