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Mon, 17 Aug 2020 10:03:20 +0000 (UTC) Subject: Re: [RFC PATCH 04/22] block/export: Add BlockExport infrastructure and block-export-add To: Kevin Wolf , qemu-block@nongnu.org References: <20200813162935.210070-1-kwolf@redhat.com> <20200813162935.210070-5-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: <7ed669db-7a75-fb25-4ce6-52369ea01b4b@redhat.com> Date: Mon, 17 Aug 2020 12:03:19 +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: <20200813162935.210070-5-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 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="Ix3dnH5mkm3OiKoXsbaBeSwcNSE8rd95j" Received-SPF: pass client-ip=207.211.31.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/17 00:24:04 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) --Ix3dnH5mkm3OiKoXsbaBeSwcNSE8rd95j Content-Type: multipart/mixed; boundary="Gs8jJ3TxdCh3CIw09NRxXoXto9W9kZLFb" --Gs8jJ3TxdCh3CIw09NRxXoXto9W9kZLFb 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: > We want to have a common set of commands for all types of block exports. > Currently, this is only NBD, but we're going to add more types. >=20 > This patch adds the basic BlockExport and BlockExportDriver structs and > a QMP command block-export-add that creates a new export based on the > given BlockExportOptions. >=20 > qmp_nbd_server_add() becomes a wrapper around qmp_block_export_add(). >=20 > Signed-off-by: Kevin Wolf > --- > qapi/block-export.json | 9 ++++++ > include/block/export.h | 32 +++++++++++++++++++++ > include/block/nbd.h | 3 +- > block/export/export.c | 57 ++++++++++++++++++++++++++++++++++++++ > blockdev-nbd.c | 19 ++++++++----- > nbd/server.c | 15 +++++++++- > Makefile.objs | 6 ++-- > block/Makefile.objs | 2 ++ > block/export/Makefile.objs | 1 + > 9 files changed, 132 insertions(+), 12 deletions(-) > create mode 100644 include/block/export.h > create mode 100644 block/export/export.c > create mode 100644 block/export/Makefile.objs Nothing of too great importance below. But it=E2=80=99s an RFC, so comment= s I will give. > diff --git a/block/export/export.c b/block/export/export.c > new file mode 100644 > index 0000000000..3d0dacb3f2 > --- /dev/null > +++ b/block/export/export.c > @@ -0,0 +1,57 @@ > +/* > + * Common block export infrastructure > + * > + * Copyright (c) 2012, 2020 Red Hat, Inc. > + * > + * Authors: > + * Paolo Bonzini > + * Kevin Wolf > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or > + * later. See the COPYING file in the top-level directory. > + */ > + > +#include "qemu/osdep.h" > + > +#include "block/export.h" > +#include "block/nbd.h" > +#include "qapi/error.h" > +#include "qapi/qapi-commands-block-export.h" > + > +static const BlockExportDriver* blk_exp_drivers[] =3D { ^^ Sternenplatzierung *hust* > + &blk_exp_nbd, > +}; Not sure whether I like this better than the block driver way of registering block drivers with a constructor. It requires writing less code, at the expense of making the variable global. So I think there=E2=80= =99s no good reason to prefer the block driver approach. Maybe my hesitance comes from the variable being declared (as extern) in a header file (block/export.h). I think I would prefer it if we put that external reference only here in this file. Would that work, or do you have other plans that require blk_exp_nbd to be visible outside of nbd/server.c and this file here? > +static const BlockExportDriver *blk_exp_find_driver(BlockExportType type= ) > +{ > + int i; > + > + for (i =3D 0; i < ARRAY_SIZE(blk_exp_drivers); i++) { > + if (blk_exp_drivers[i]->type =3D=3D type) { > + return blk_exp_drivers[i]; > + } > + } How bad would it be to define blk_exp_drivers as blk_exp_drivers[BLOCK_EXPORT_TYPE__MAX] and use the BlockExportType as the driver index so we don=E2=80=99t have to loop here? Not that it matters performance-wise. Just something I wondered. > + return NULL; Why not e.g. g_assert_not_reached()? (If the BlockExportType were used as the index, I=E2=80=99d assert that type < ARRAY_SIZE(blk_exp_drivers) && blk_exp_drivers[type] !=3D NULL. I don=E2=80=99t think there=E2=80=99s a reason for graceful handling.) > +} [...] > +void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp) > +{ > + BlockExportOptions export =3D { > + .type =3D BLOCK_EXPORT_TYPE_NBD, > + .u.nbd =3D *arg, > + }; > + qmp_block_export_add(&export, errp); > +} Hm. I think I=E2=80=99d=E2=80=99ve kept this in blockdev-nbd.c, actually, = but, well. It=E2=80=99ll stay a one-off. > diff --git a/blockdev-nbd.c b/blockdev-nbd.c > index 98ee1b6170..a1dc11bdd7 100644 > --- a/blockdev-nbd.c > +++ b/blockdev-nbd.c [...] > @@ -217,6 +220,8 @@ void qmp_nbd_server_add(BlockExportOptionsNbd *arg, E= rror **errp) > =20 > out: > aio_context_release(aio_context); > + /* TODO Remove the cast: Move to server.c which can access fields of= exp */ > + return (BlockExport*) exp; *hust* (But if it=E2=80=99s moved soon anyway so we can use &exp->common, then wha= tever.) 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