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Thu, 16 Jul 2020 15:21:15 +0000 (UTC) Subject: Re: [PATCH v7 21/47] block: Use CAFs in bdrv_refresh_filename() To: Andrey Shinkevich , qemu-block@nongnu.org References: <20200625152215.941773-1-mreitz@redhat.com> <20200625152215.941773-22-mreitz@redhat.com> <71aca7a2-ebb0-92f3-c943-6a876cf9f57c@virtuozzo.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: Thu, 16 Jul 2020 17:21:13 +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: <71aca7a2-ebb0-92f3-c943-6a876cf9f57c@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dV5xJVFDp8QD07tFO5v3qIDpFT5gkUHF3" Received-SPF: pass client-ip=207.211.31.81; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/16 04:55:15 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=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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , 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) --dV5xJVFDp8QD07tFO5v3qIDpFT5gkUHF3 Content-Type: multipart/mixed; boundary="S23NKnYuVzbRFgUfKgC4l8XmIW6h520kT" --S23NKnYuVzbRFgUfKgC4l8XmIW6h520kT Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 15.07.20 14:52, Andrey Shinkevich wrote: > On 25.06.2020 18:21, Max Reitz wrote: >> bdrv_refresh_filename() and the kind of related bdrv_dirname() should >> look to the primary child when they wish to copy the underlying file's >> filename. >> >> Signed-off-by: Max Reitz >> --- >> =C2=A0 block.c | 29 +++++++++++++++++++++-------- >> =C2=A0 1 file changed, 21 insertions(+), 8 deletions(-) >> >> diff --git a/block.c b/block.c >> index 8131d0b5eb..7c827fefa0 100644 >> --- a/block.c >> +++ b/block.c >> @@ -6797,6 +6797,7 @@ void bdrv_refresh_filename(BlockDriverState *bs) >> =C2=A0 { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BlockDriver *drv =3D bs->drv; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BdrvChild *child; >> +=C2=A0=C2=A0=C2=A0 BlockDriverState *primary_child_bs; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 QDict *opts; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bool backing_overridden; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bool generate_json_filename; /* Whether o= ur default >> implementation should >> @@ -6866,20 +6867,30 @@ void bdrv_refresh_filename(BlockDriverState *bs) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 qobject_unref(bs->full_open_options); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bs->full_open_options =3D opts; >> =C2=A0 +=C2=A0=C2=A0=C2=A0 primary_child_bs =3D bdrv_primary_bs(bs); >> + >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (drv->bdrv_refresh_filename) { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Obsolete infor= mation is of no use here, so drop the old >> file name >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * informati= on before refreshing it */ >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bs->exact_filenam= e[0] =3D '\0'; >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 drv->bdrv_= refresh_filename(bs); >> -=C2=A0=C2=A0=C2=A0 } else if (bs->file) { >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Try to reconstruct valid = information from the underlying >> file */ >> +=C2=A0=C2=A0=C2=A0 } else if (primary_child_bs) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Try to reconstruct v= alid information from the underlying >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * file -- this only wo= rks for format nodes (filter nodes >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * cannot be probed and= as such must be selected by the user >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * either through an op= tions dict, or through a special >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * filename which the f= ilter driver must construct in its >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * .bdrv_refresh_filena= me() implementation). >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >=20 >=20 > The caller may not be aware of a filter node and intend to refresh the > name of underlying format node. >=20 > In that case, the filter driver should redirect the call to the format > node. It shouldn=E2=80=99t. We can only return a plain filename if passing that filename to qemu (e.g. to -drive) will result in the same block graph configuration. This is what the comment means by =E2=80=9Cfilter nodes cannot be probed=E2= =80=9D: If there is a filter node, we must generate a json:{} filename, because otherwise reopening the block device with -drive by passing the filename generated here would result in a configuration where the filter is missing. > What are situations the name of the filter itself should be refreshed in? Hypothetically, if a filename could specify a filter. For example, say the filename =E2=80=9Cfilter[copy-on-read]:foo.qcow2=E2=80=9D would result = in qemu creating a COR filter on top of a qcow2 node, then we could generate such a filename. In practice, filters cannot be configured through plain filenames (apart from blkverify, but that=E2=80=99s a debugging feature, so it doesn=E2=80= =99t really matter), so there is no such situation. All filter nodes should have an empty exact_filename and thus get a json:{} pseudo-filename. > If there are any, should we do both actions or choose either? >=20 > Andrey >=20 >=20 >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bs->exact_= filename[0] =3D '\0'; >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * We can us= e the underlying file's filename if: >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * - it has = a filename, >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * - the current BDS is= not a filter, >=20 >=20 > Should we check the function input parameter for being a filter's BS > here, in this function, and handle the case here or let the filter > driver function do that or else the caller should check it? bdrv_refresh_filename() is called whenever some node in the block graph has changed, just to refresh its filename (after that change). The caller generally doesn=E2=80=99t really care about the result, so it doesn= =E2=80=99t matter whether the node is a filter or not (i.e., whether it gets a plain filename or not). I don=E2=80=99t think the caller should check it, and in this implementatio= n we simply have to handle filter nodes correctly: That is, not give them a plain filename. Max --S23NKnYuVzbRFgUfKgC4l8XmIW6h520kT-- --dV5xJVFDp8QD07tFO5v3qIDpFT5gkUHF3 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl8QcGkACgkQ9AfbAGHV z0BofggAkwzQhfyj+8rJ74QGShl+1QUc2u080vnw6evV2EDs39oOOdyxd8HvVrxH GRZt42Vcx/xCoW37/jYnSvFXvdT+7VtcDz32xQnqUg0kwncAbZ+ooNICKlZx/HVl 3ZHgMTiIGwGJvvG5nIHv8/SBrSjBNEd925+awpbIxME1yzHYKMmshr7TYTRV5HUo MMhXVYF67Pbrkll5iHpOePVVU91aCidWck4/zdJ9ZnmTfYExoBa+rrXkcie8c0lE z7k3hAygASRCAv+/bmzOkoin8Ra2V8B8WoO8HzTWO3JBfJfEFo5s5p9w+mw/JAzy KDbQo9mDemtXdoh6NaUBqkxcOnluag== =Rnla -----END PGP SIGNATURE----- --dV5xJVFDp8QD07tFO5v3qIDpFT5gkUHF3--