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Wed, 23 Nov 2022 16:04:43 +0000 Message-ID: <9cdace7b-7fd2-7c9a-01a2-14bef1473136@nutanix.com> Date: Wed, 23 Nov 2022 21:34:35 +0530 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH v4 2/2] migration: check magic value for deciding the mapping of channels To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: qemu-devel@nongnu.org, peterx@redhat.com, prerna.saxena@nutanix.com, quintela@redhat.com, dgilbert@redhat.com, lsoaresp@redhat.com References: <20221123150527.24608-1-manish.mishra@nutanix.com> <20221123150527.24608-3-manish.mishra@nutanix.com> From: "manish.mishra" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SJ0PR03CA0354.namprd03.prod.outlook.com (2603:10b6:a03:39c::29) To PH0PR02MB7384.namprd02.prod.outlook.com (2603:10b6:510:12::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR02MB7384:EE_|SA0PR02MB7210:EE_ X-MS-Office365-Filtering-Correlation-Id: e8ea4ae0-b60c-43e0-9081-08dacd6c6f3b x-proofpoint-crosstenant: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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envelope-from=manish.mishra@nutanix.com; helo=mx0b-002c1b01.pphosted.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, NICE_REPLY_A=-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 23/11/22 9:28 pm, Daniel P. Berrangé wrote: > On Wed, Nov 23, 2022 at 03:05:27PM +0000, manish.mishra wrote: >> Current logic assumes that channel connections on the destination side are >> always established in the same order as the source and the first one will >> always be the main channel followed by the multifid or post-copy >> preemption channel. This may not be always true, as even if a channel has a >> connection established on the source side it can be in the pending state on >> the destination side and a newer connection can be established first. >> Basically causing out of order mapping of channels on the destination side. >> Currently, all channels except post-copy preempt send a magic number, this >> patch uses that magic number to decide the type of channel. This logic is >> applicable only for precopy(multifd) live migration, as mentioned, the >> post-copy preempt channel does not send any magic number. Also, tls live >> migrations already does tls handshake before creating other channels, so >> this issue is not possible with tls, hence this logic is avoided for tls >> live migrations. This patch uses read peek to check the magic number of >> channels so that current data/control stream management remains >> un-effected. >> >> Reviewed-by: Peter Xu >> Reviewed-by: Daniel P. Berrangé > Suggested-by: Daniel P. Berrangé > Signed-off-by: manish.mishra >> --- >> migration/channel.c | 46 ++++++++++++++++++++++++++++++++++++++++ >> migration/channel.h | 5 +++++ >> migration/migration.c | 45 ++++++++++++++++++++++++++++----------- >> migration/multifd.c | 12 ++++------- >> migration/multifd.h | 2 +- >> migration/postcopy-ram.c | 5 +---- >> migration/postcopy-ram.h | 2 +- >> 7 files changed, 91 insertions(+), 26 deletions(-) >> >> diff --git a/migration/channel.c b/migration/channel.c >> index 1b0815039f..a4600f52c5 100644 >> --- a/migration/channel.c >> +++ b/migration/channel.c >> @@ -92,3 +92,49 @@ void migration_channel_connect(MigrationState *s, >> migrate_fd_connect(s, error); >> error_free(error); >> } >> + >> + >> +/** >> + * @migration_channel_read_peek - Read from the peek of migration channel, >> + * without actually removing it from channel buffer. >> + * >> + * @ioc: the channel object >> + * @buf: the memory region to read data into >> + * @buflen: the number of bytes to read in @buf >> + * @errp: pointer to a NULL-initialized error object >> + * >> + * Returns 0 if successful, returns -1 and sets @errp if fails. >> + */ >> +int migration_channel_read_peek(QIOChannel *ioc, >> + const char *buf, >> + const size_t buflen, >> + Error **errp) >> +{ >> + ssize_t len = 0; >> + struct iovec iov = { .iov_base = (char *)buf, .iov_len = buflen }; >> + >> + while (len < buflen) { >> + len = qio_channel_readv_full(ioc, &iov, 1, NULL, >> + NULL, QIO_CHANNEL_READ_FLAG_MSG_PEEK, errp); >> + >> + if (len == QIO_CHANNEL_ERR_BLOCK) { >> + if (qemu_in_coroutine()) { >> + /* 1ms sleep. */ >> + qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 1000000); >> + } else { >> + qio_channel_wait(ioc, G_IO_IN); >> + } >> + continue; >> + } >> + if (len == 0) { >> + error_setg(errp, >> + "Unexpected end-of-file on channel"); >> + return -1; >> + } >> + if (len < 0) { >> + return -1; >> + } >> + } > This busy waits when len > 0 and < buflen > > > With regards, > Daniel Sorry,   Daniel, may be i misunderstood something from earlier discussions. I thought we discussed we may not prevent it from looping multiple times but we can  qemu_co_sleep_ns after every retry to deal with busy wait? Thanks Manish Mishra