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Thu, 7 May 2020 08:49:19 +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> 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: <7d226c94-2f14-eddb-b795-f8a961023947@redhat.com> Date: Thu, 7 May 2020 10:49:17 +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: <20200506103722.GB6333@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="XJL9UXjnNVfCqg5hRGcUPHHgUkIN9dfsM" 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, RCVD_IN_MSPIKE_H2=-0.001, 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) --XJL9UXjnNVfCqg5hRGcUPHHgUkIN9dfsM Content-Type: multipart/mixed; boundary="fRBdyO9iKXoZZYyzxABrzEY8HlCWT20IL" --fRBdyO9iKXoZZYyzxABrzEY8HlCWT20IL Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 06.05.20 12:37, Kevin Wolf wrote: > 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_f= lags, 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? >> + */ >> + >> + /* >> + * Pure and non-filtered data children of non-format nodes should >> + * be probed by default (even when the node itself has BDRV_O_PROTO= COL >> + * set). This only affects a very limited set of drivers (namely >> + * quorum and blkverify when this comment was written). >> + * Force-clear BDRV_O_PROTOCOL then. >> + */ >> + if (!parent_is_format && >> + (role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA | >> + BDRV_CHILD_FILTERED)) =3D=3D >> + BDRV_CHILD_DATA) >=20 > You could avoid the odd indentation (I can't decide whether or not it > should be one space more to align correctly) and probably also make the > expression more readable if you split it into: >=20 > (role & BDRV_CHILD_DATA) && > !(role & (BDRV_CHILD_METADATA | BDRV_CHILD_FILTERED)) Yes, looks good. >> + { >> + flags &=3D ~BDRV_O_PROTOCOL; >> + } >> + >> + /* >> + * All children of format nodes (except for COW children) and all >> + * metadata children in general should never be format-probed. >> + * Force-set BDRV_O_PROTOCOL then. >> + */ >> + if ((parent_is_format && !(role & BDRV_CHILD_COW)) || >> + (role & BDRV_CHILD_METADATA)) >> + { >> + flags |=3D BDRV_O_PROTOCOL; >> + } >> + >> + /* >> + * If the cache mode isn't explicitly set, inherit direct and no-fl= ush from >> + * the parent. >> + */ >> + qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_DI= RECT); >> + qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_NO= _FLUSH); >> + qdict_copy_default(child_options, parent_options, BDRV_OPT_FORCE_SH= ARE); >> + >> + if (role & BDRV_CHILD_COW) { >> + /* backing files are always opened read-only */ >=20 > Not "always", just by default. OK. I just copied the comment from bdrv_backing_options(). >> + qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "on"); >> + qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "= off"); >> + } else { >> + /* Inherit the read-only option from the parent if it's not set= */ >> + qdict_copy_default(child_options, parent_options, BDRV_OPT_READ= _ONLY); >> + qdict_copy_default(child_options, parent_options, >> + BDRV_OPT_AUTO_READ_ONLY); >> + } >> + >> + 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")= ; >> + } >=20 > Why the restriction to format here? Don't we break "unmap" propagation > through filters with this? Right now (before this series), the behavior seems ambiguous, in that for filters that use bs->file, it is set, but for those that use bs->backing, it isn=E2=80=99t. But I suspect the main reason for what I did is the way I interpreted the comment (which before this series only mentions block drivers in general, not specifically format drivers): It sounded to me as if the block driver needed to respect the unmap policy, and I didn=E2=80=99t think filters did that. So it was my understanding that filter drivers would just propagate discards and thus we couldn=E2=80=99t default-enable unmap o= n their children. But I was wrong, the block driver doesn=E2=80=99t need to respect anything, because bdrv_co_pdiscard() already does. So I suppose it should indeed be enabled for all children, with the comment changed to express that it isn=E2=80=99t any block driver that resp= ects unmap policy, but bdrv_co_pdiscard(), e.g.: bdrv_co_pdiscard() respects unmap policy for the parent, so we can default to enable it on lower layers regardless of the parent option. > It would probably also be a good question why we don't propagate it to > the backing file, but this is preexisting. I suppose we should, although it=E2=80=99s irrelevant, so. I suppose I=E2= =80=99ll just drop the parent_is_format, adjust the comment and that should be fine for this series. Max --fRBdyO9iKXoZZYyzxABrzEY8HlCWT20IL-- --XJL9UXjnNVfCqg5hRGcUPHHgUkIN9dfsM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6zy40ACgkQ9AfbAGHV z0AoMwgAkxyDoRcFWFlAXMzWaTNajiievWxXB+BOMyNoyDdKlKZ0dkgnMZYUMyBF sGe2zjRE/TagnZdm35kHsZpZ9tqVou8bbX9YzsxNKkz5lkRArdNjxfFctWQZ3o9h U4PUKPz8s4N8OVy4XwySKAGAwQsZkz2Jw4ag0TnP+MhoEdqJ25MYWGT6C42cIncR c6LV9YAtUNjjqeGHp45cfKS/UUf3PWzrBTsGz9C1cqQcq7zJqb0GCbAd5pzmOxQ4 xRbpoxkz7Rd4H74vA3f76cK+Y9Oxq01W6B4UQgKUN7X5vPtLPEwDOcNlslkcKx+/ x1Is+2LUXNnoa+lv7eKkPoptf2N/Qg== =0Sj2 -----END PGP SIGNATURE----- --XJL9UXjnNVfCqg5hRGcUPHHgUkIN9dfsM--