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Thu, 7 May 2020 09:18:17 +0000 (UTC) Subject: Re: [PATCH v3 09/33] block: Add generic bdrv_inherited_options() To: Kevin Wolf References: <20200218124242.584644-1-mreitz@redhat.com> <20200218124242.584644-10-mreitz@redhat.com> <20200506103722.GB6333@linux.fritz.box> <20200506131135.GE6333@linux.fritz.box> 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: <7b7084ea-fb31-c994-cae0-f9a2c8438ae1@redhat.com> Date: Thu, 7 May 2020 11:18:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200506131135.GE6333@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="C8K6OzaxsYUYFvqwL9X8KlzQo5MHDUzGA" Received-SPF: pass client-ip=205.139.110.61; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/07 02:00:54 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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, qemu-block@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) --C8K6OzaxsYUYFvqwL9X8KlzQo5MHDUzGA Content-Type: multipart/mixed; boundary="pkdazhM8xI4hMTMMG6UY1KDFbBPajJRP3" --pkdazhM8xI4hMTMMG6UY1KDFbBPajJRP3 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 06.05.20 15:11, Kevin Wolf wrote: > Am 06.05.2020 um 12:37 hat Kevin Wolf geschrieben: >> Am 18.02.2020 um 13:42 hat Max Reitz geschrieben: >>> After the series this patch belongs to, we want to have a common >>> BdrvChildClass that encompasses all of child_file, child_format, and >>> child_backing. Such a single class needs a single .inherit_options() >>> implementation, and this patch introduces it. >>> >>> The next patch will show how the existing implementations can fall back >>> to it just by passing appropriate BdrvChildRole and parent_is_format >>> values. >>> >>> Signed-off-by: Max Reitz >>> Reviewed-by: Eric Blake >>> --- >>> block.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 84 insertions(+) >>> >>> diff --git a/block.c b/block.c >>> index c33f0e9b42..9179b9b604 100644 >>> --- a/block.c >>> +++ b/block.c >>> @@ -998,6 +998,90 @@ static void bdrv_temp_snapshot_options(int *child_= flags, QDict *child_options, >>> *child_flags &=3D ~BDRV_O_NATIVE_AIO; >>> } >>> =20 >>> +/* >>> + * Returns the options and flags that a generic child of a BDS should >>> + * get, based on the given options and flags for the parent BDS. >>> + */ >>> +static void __attribute__((unused)) >>> + bdrv_inherited_options(BdrvChildRole role, bool parent_is_format, >>> + int *child_flags, QDict *child_options, >>> + int parent_flags, QDict *parent_options) >>> +{ >>> + int flags =3D parent_flags; >>> + >>> + /* >>> + * First, decide whether to set, clear, or leave BDRV_O_PROTOCOL. >>> + * Generally, the question to answer is: Should this child be >>> + * format-probed by default? >>> + */ >=20 > Just for clarity: Do you know a good reason to ever leave it (i.e. > inherit it from the parent), except that that's what we have always been > doing for backing files? Though of course, only formats have backing > files, so the flag would never be set in practice in this case. It seems correct for filters. [...] >>> + if (parent_is_format && !(role & BDRV_CHILD_COW)) { >>> + /* >>> + * Our format drivers take care to send flushes and respect >>> + * unmap policy, so we can default to enable both on lower >>> + * layers regardless of the corresponding parent options. >>> + */ >>> + qdict_set_default_str(child_options, BDRV_OPT_DISCARD, "unmap"= ); >>> + } >> >> Why the restriction to format here? Don't we break "unmap" propagation >> through filters with this? >> >> It would probably also be a good question why we don't propagate it to >> the backing file, but this is preexisting. >=20 > Some patches later, I think the fix is an else branch that copies the > flag from parent_options. I thought about the same thing, but is that really necessary if bdrv_co_pdiscard() will already suppress discards on the parent if unmap is false? Max --pkdazhM8xI4hMTMMG6UY1KDFbBPajJRP3-- --C8K6OzaxsYUYFvqwL9X8KlzQo5MHDUzGA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6z0lgACgkQ9AfbAGHV z0A4oQf/Q8XeI41Qx7VzT77NFo0MyeALYc3vA1yB7tki4sxl0Knnog9A+iApSM24 f5dN0nEtF9oCh85MQ/NXTS6lZZdEIJkqY+IZi0ij5VwW2iZkXZ1zBdsLvPyQAWi1 qKSARkVEhCegvTadfIx2UNNaqvgmepYCz3FetNGE3X+xEpLKkAUT6tbzS4CCdgA8 hA2KyUaYV/nWRZ/+D/584ZP7n6HRybhI9wsS8ifXuXSlMSSyNmwkhayX65vreFpn ms8xRpylh+5WBcqghHzCL5mpIGBCR9KponyeonaHFf2sgdb34jaIlWWghpa813uY 5nfjIW5Mq9l0tL3738QRKvgFi+slrw== =pUap -----END PGP SIGNATURE----- --C8K6OzaxsYUYFvqwL9X8KlzQo5MHDUzGA--