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Fri, 9 Oct 2020 10:10:18 +0200 (CEST) From: Markus Armbruster To: Eric Blake Subject: Re: [PATCH v3 2/6] nbd: Add 'qemu-nbd -A' to expose allocation depth References: <20201009020714.1074061-1-eblake@redhat.com> <20201009020714.1074061-3-eblake@redhat.com> Date: Fri, 09 Oct 2020 10:10:18 +0200 In-Reply-To: <20201009020714.1074061-3-eblake@redhat.com> (Eric Blake's message of "Thu, 8 Oct 2020 21:07:10 -0500") Message-ID: <87lfgfom51.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/09 02:34:37 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org, rjones@redhat.com, qemu-devel@nongnu.org, Max Reitz , stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > Allow the server to expose an additional metacontext to be requested > by savvy clients. qemu-nbd adds a new option -A to expose the > qemu:allocation-depth metacontext through NBD_CMD_BLOCK_STATUS; this > can also be set via QMP when using block-export-add. > > qemu as client can be hacked into viewing this new context by using > the now-misnamed x-dirty-bitmap option when creating an NBD blockdev > (even though our x- naming means we could rename it, I did not think > it worth breaking back-compat of tools that have been using it while > waiting for a better solution). It is worth noting the decoding of > how such context information will appear in 'qemu-img map > --output=json': > > NBD_STATE_DEPTH_UNALLOC => "zero":false, "data":true > NBD_STATE_DEPTH_LOCAL => "zero":false, "data":false > NBD_STATE_DEPTH_BACKING => "zero":true, "data":true > > libnbd as client is probably a nicer way to get at the information > without having to decipher such hacks in qemu as client. ;) > > Signed-off-by: Eric Blake > Message-Id: <20200930121105.667049-6-eblake@redhat.com> > Reviewed-by: Vladimir Sementsov-Ogievskiy > [eblake: comment tweak suggested by Vladimir] > Signed-off-by: Eric Blake > --- [...] > diff --git a/qapi/block-core.json b/qapi/block-core.json > index 3758ea991269..249bd434f4eb 100644 > --- a/qapi/block-core.json > +++ b/qapi/block-core.json > @@ -3882,9 +3882,12 @@ > # > # @tls-creds: TLS credentials ID > # > -# @x-dirty-bitmap: A "qemu:dirty-bitmap:NAME" string to query in place of > +# @x-dirty-bitmap: A metacontext name such as "qemu:dirty-bitmap:NAME" or What is a "metacontext"? Aside: nbd.h spells it "meta context". The two spellings suggest different meanings to me. Using meta- as a prefix modifies the prefixed word, as in metadata (data that provides information about other data). Separated by space, meta becomes a noun. None of its common meanings seem to apply here. Recommend to pick an appropriate one of "metacontext", "meta-context", "meta context", and stick to it. > +# "qemu:allocation-depth" to query in place of the > # traditional "base:allocation" block status (see > -# NBD_OPT_LIST_META_CONTEXT in the NBD protocol) (since 3.0) > +# NBD_OPT_LIST_META_CONTEXT in the NBD protocol; and > +# yes, naming this option x-context would have made > +# more sense) (since 3.0) > # > # @reconnect-delay: On an unexpected disconnect, the nbd client tries to > # connect again until succeeding or encountering a serious > diff --git a/qapi/block-export.json b/qapi/block-export.json > index 65804834d905..524cd3a94400 100644 > --- a/qapi/block-export.json > +++ b/qapi/block-export.json > @@ -78,11 +78,15 @@ > # NBD client can use NBD_OPT_SET_META_CONTEXT with > # "qemu:dirty-bitmap:NAME" to inspect the bitmap. (since 4.0) > # > +# @alloc: Also export the allocation map for @device, so the NBD client > +# can use NBD_OPT_SET_META_CONTEXT with "qemu:allocation-depth" > +# to inspect allocation details. (since 5.2) > +# > # Since: 5.0 > ## > { 'struct': 'BlockExportOptionsNbd', > 'data': { '*name': 'str', '*description': 'str', > - '*bitmap': 'str' } } > + '*bitmap': 'str', '*alloc': 'bool' } } > > ## > # @NbdServerAddOptions: [...]