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Mon, 17 Aug 2020 12:56:12 +0000 (UTC) Subject: Re: [RFC PATCH 09/22] nbd: Add writethrough to block-export-add To: Kevin Wolf , qemu-block@nongnu.org References: <20200813162935.210070-1-kwolf@redhat.com> <20200813162935.210070-10-kwolf@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Mon, 17 Aug 2020 14:56:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200813162935.210070-10-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Do6uDWcxBknsNfvClftG0uZ3b0ZF2yDmr" Received-SPF: pass client-ip=205.139.110.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/17 05:13:21 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --Do6uDWcxBknsNfvClftG0uZ3b0ZF2yDmr Content-Type: multipart/mixed; boundary="FNIdvyaFu8hPKaWUVp7XmORIIhMeiN8HR" --FNIdvyaFu8hPKaWUVp7XmORIIhMeiN8HR Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 13.08.20 18:29, Kevin Wolf wrote: > qemu-nbd allows use of writethrough cache modes, which mean that write > requests made through NBD will cause a flush before they complete. > Expose the same functionality in block-export-add. >=20 > Signed-off-by: Kevin Wolf > --- > qapi/block-export.json | 7 ++++++- > blockdev-nbd.c | 2 +- > 2 files changed, 7 insertions(+), 2 deletions(-) >=20 > diff --git a/qapi/block-export.json b/qapi/block-export.json > index 1fdc55c53a..4ce163411f 100644 > --- a/qapi/block-export.json > +++ b/qapi/block-export.json > @@ -167,10 +167,15 @@ > # Describes a block export, i.e. how single node should be exported on a= n > # external interface. > # > +# @writethrough: If true, caches are flushed after every write request t= o the > +# export before completion is signalled. (since: 5.2; > +# default: false) > +# > # Since: 4.2 > ## > { 'union': 'BlockExportOptions', > - 'base': { 'type': 'BlockExportType' }, > + 'base': { 'type': 'BlockExportType', > + '*writethrough': 'bool' }, > 'discriminator': 'type', > 'data': { > 'nbd': 'BlockExportOptionsNbd' Hm. I find it weird to have @writethrough in the base but @device in the specialized class. I think everything that will be common to all block exports should be in the base, and that probably includes a node-name. I=E2=80=99m aware that w= ill make things more tedious in the code, but perhaps it would be a nicer interface in the end. Or is the real problem that that would create problems in the storage daemon=E2=80=99s command line interface, because th= en the specialized (legacy) NBD interface would no longer be compatible with the new generalized block export interface? Anyway, @writable might be a similar story. A @read-only may make sense in general, I think. Basically, I think that the export code should be separate from the code setting up the BlockBackend that should be exported, so all options regarding that BB should be common; and those options are @node-name, @writethrough, and @read-only. (And perhaps other things like @resizable, too, even though that isn=E2=80=99t something to consider for N= BD.) Max --FNIdvyaFu8hPKaWUVp7XmORIIhMeiN8HR-- --Do6uDWcxBknsNfvClftG0uZ3b0ZF2yDmr Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl86fmoACgkQ9AfbAGHV z0ChSwgAiB1Wl4kaSH/MH0KE20qv3AlXImFdzrNcP4MCfosQdE+GgaePkUgfYsNz LaFx+Eggbb6GBxCZcG+3lRDDVio1jDa9B5VFGEt3mRUDXuVb1UlP9nmQP1V5tPtT f617947yfqnXcbH3fsVNiuWYWy9Zqn780KiSaMxa+JA/rdsiiEux5DzsWE94SH1a Scxn8jcSig0yIDo+SakHDMXh4j70GBJvu3ZccQT7sSw567169DsWbpMypFwmyCc6 gVwtihur+PF9nX0KHYabfwJfQyUrkbP0kRUKIzd8mobu6rwuglhpuGE1MwDw+pRQ t4d7F8VP4HEaojO+Pz1iwPOB44c/yA== =GE/J -----END PGP SIGNATURE----- --Do6uDWcxBknsNfvClftG0uZ3b0ZF2yDmr--