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Tsirkin" , Jason Wang , Alex Williamson , Cedric Le Goater , Gerd Hoffmann , Marc-Andre Lureau , David Hildenbrand Subject: Re: [PATCH V4 13/14] migration: update cpr-reboot description In-Reply-To: <1708622920-68779-14-git-send-email-steven.sistare@oracle.com> (Steve Sistare's message of "Thu, 22 Feb 2024 09:28:39 -0800") References: <1708622920-68779-1-git-send-email-steven.sistare@oracle.com> <1708622920-68779-14-git-send-email-steven.sistare@oracle.com> Date: Wed, 28 Feb 2024 08:12:11 +0100 Message-ID: <87h6ht3vw4.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@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=-0.088, 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_H2=-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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Steve Sistare writes: > Clarify qapi for cpr-reboot migration mode, and add vfio support. The patch only affects documentation, but that's less than clear from the commit message. Suggest Improve documentation for migration mode @cpr-reboot. In particular, document VFIO support. > Signed-off-by: Steve Sistare > --- > qapi/migration.json | 35 ++++++++++++++++++++++------------- > 1 file changed, 22 insertions(+), 13 deletions(-) > > diff --git a/qapi/migration.json b/qapi/migration.json > index 5a565d9..0990297 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -636,19 +636,28 @@ > # > # @normal: the original form of migration. (since 8.2) > # > -# @cpr-reboot: The migrate command saves state to a file, allowing one to > -# quit qemu, reboot to an updated kernel, and restart an updated > -# version of qemu. The caller must specify a migration URI > -# that writes to and reads from a file. Unlike normal mode, > -# the use of certain local storage options does not block the > -# migration, but the caller must not modify guest block devices > -# between the quit and restart. To avoid saving guest RAM to the > -# file, the memory backend must be shared, and the @x-ignore-shared > -# migration capability must be set. Guest RAM must be non-volatile > -# across reboot, such as by backing it with a dax device, but this > -# is not enforced. The restarted qemu arguments must match those > -# used to initially start qemu, plus the -incoming option. > -# (since 8.2) > +# @cpr-reboot: The migrate command stops the VM and saves state to the URI. > +# After quitting qemu, the user resumes by running qemu -incoming. These two sentences apply to any migration mode, don't they? Just checking I understand. > +# > +# This mode allows the user to quit qemu, and restart an updated version > +# of qemu. The user may even update and reboot the OS before restarting, > +# as long as the URI persists across a reboot. Hmm, doesn't normal migration also support migrating to a newer QEMU? > +# > +# Unlike normal mode, the use of certain local storage options does not > +# block the migration, but the user must not modify guest block devices > +# between the quit and restart. "Must not modify the contents of the guest block devices"? > +# > +# This mode supports vfio devices provided the user first puts the guest "VFIO devices" > +# in the suspended runstate, such as by issuing guest-suspend-ram to the > +# qemu guest agent. > +# > +# Best performance is achieved when the memory backend is shared and the > +# @x-ignore-shared migration capability is set, but this is not required. > +# Further, if the user reboots before restarting such a configuration, the > +# shared backend must be be non-volatile across reboot, such as by backing Typo: "be be non-volatile" Suggest "the shared memory must persist" > +# it with a dax device. > +# > +# (since 8.2) > ## > { 'enum': 'MigMode', > 'data': [ 'normal', 'cpr-reboot' ] } Thanks for adjusting indentation to conform to conventions. Please additionally reflow the text to limit line length to 70 characters.