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Tue, 12 May 2020 06:19:43 +0000 (UTC) Subject: Re: [PATCH v3 3/9] block: Make it easier to learn which BDS support bitmaps To: Eric Blake , qemu-devel@nongnu.org References: <20200508180340.675712-1-eblake@redhat.com> <20200508180340.675712-4-eblake@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: Tue, 12 May 2020 08:19:41 +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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ZdWUiVHyyanP6F6jKwFpZHJO6zneu5yju" 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 = 2020/05/12 02:02:04 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: kwolf@redhat.com, Vladimir Sementsov-Ogievskiy , John Snow , 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) --ZdWUiVHyyanP6F6jKwFpZHJO6zneu5yju Content-Type: multipart/mixed; boundary="rbLs3AcreBqFWJWPqXZsuNkXcg23eN9LH" --rbLs3AcreBqFWJWPqXZsuNkXcg23eN9LH Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 11.05.20 20:16, Eric Blake wrote: > On 5/11/20 4:21 AM, Max Reitz wrote: >> On 08.05.20 20:03, Eric Blake wrote: >>> Upcoming patches will enhance bitmap support in qemu-img, but in doing >>> so, it turns out to be nice to suppress output when bitmaps make no >>> sense (such as on a qcow2 v2 image).=C2=A0 Add a hook to make this easi= er >>> to query. >>> >>> In the future, when we improve the ability to look up bitmaps through >>> a filter, we will probably also want to teach the block layer to >>> automatically let filters pass this request on through. >>> >>> Signed-off-by: Eric Blake >>> --- >>> =C2=A0 block/qcow2.h=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 | 1 + >>> =C2=A0 include/block/block_int.h=C2=A0=C2=A0=C2=A0 | 1 + >>> =C2=A0 include/block/dirty-bitmap.h | 1 + >>> =C2=A0 block/dirty-bitmap.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 | 9 +++++++++ >>> =C2=A0 block/qcow2-bitmap.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 | 7 +++++++ >>> =C2=A0 block/qcow2.c=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 | 1 + >>> =C2=A0 6 files changed, 20 insertions(+) >>> >>> diff --git a/block/qcow2.h b/block/qcow2.h >>> index f4de0a27d5c3..fb2b2b5a7b4d 100644 >>> --- a/block/qcow2.h >>> +++ b/block/qcow2.h >>> @@ -764,6 +764,7 @@ bool >>> qcow2_co_can_store_new_dirty_bitmap(BlockDriverState *bs, >>> =C2=A0 int qcow2_co_remove_persistent_dirty_bitmap(BlockDriverState *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=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=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const char *name, >>> =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=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=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Error **errp); >>> +bool qcow2_dirty_bitmap_supported(BlockDriverState *bs); >>> >>> =C2=A0 ssize_t coroutine_fn >>> =C2=A0 qcow2_co_compress(BlockDriverState *bs, void *dest, size_t dest_= size, >>> diff --git a/include/block/block_int.h b/include/block/block_int.h >>> index df6d0273d679..cb1082da4c43 100644 >>> --- a/include/block/block_int.h >>> +++ b/include/block/block_int.h >>> @@ -560,6 +560,7 @@ struct BlockDriver { >>> =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=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 uint64_t parent_perm, uint64_t >>> parent_shared, >>> =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=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 uint64_t *nperm, uint64_t *nshared); >>> >>> +=C2=A0=C2=A0=C2=A0 bool (*bdrv_dirty_bitmap_supported)(BlockDriverStat= e *bs); >> >> All BDSs support bitmaps, but only some support persistent dirty >> bitmaps, so I think the name should reflect that. >=20 > How about .bdrv_dirty_bitmap_supports_persistent? Sure. Or .bdrv_supports_persistent_dirty_bitmaps. Or .bdrv_persistent_dirty_bitmaps_supported. You decide what sounds best. :) >> Conceptually, this looks reasonable.=C2=A0 This information might indeed= be >> nice to have, and I=E2=80=99m not sure whether we should extend any exis= ting >> interface to return it. >> >> (The interfaces that come to my mind are: >> (1) bdrv_can_store_new_dirty_bitmap() below, which we could make accept >> a NULL @name to return basically the same information.=C2=A0 But it=E2= =80=99s still a >> bit different, because I=E2=80=99d expect that function to return whethe= r any >> bitmap can be stored then, not whether the node supports bitmaps at all. >> =C2=A0 So e.g. if there are already too many bitmaps, it should return f= alse, >> even though the node itself does support bitmaps. >=20 > [which reminds me - a while ago, we had patches for qcow2 handling with > 64k bitmaps, or whatever insane number it took to overflow data > structures, and I don't know if those ever got applied...] I think that was a1db8733d28. As far as I remember I just didn=E2=80=99t m= erge the test, because it took like five minutes to run. >> (2) bdrv_get_info()/BlockDriverInfo: This information would fit in very >> nicely here, but do we have to put it here just because it does?=C2=A0 I >> don=E2=80=99t think so.=C2=A0 This patch adds 20 lines of code, that sho= ws that it=E2=80=99s >> very simple to add a dedicated method, and it=E2=80=99s certainly a bit = easier >> to use than to invoke bdrv_get_info() and throw away all the other >> information.=C2=A0 Perhaps this patch only shows that BlockDriverInfo do= esn=E2=80=99t >> make much sense in the first place, and most of its fields should have >> been scalar return values from dedicated functions.) >=20 > Indeed, you (re-)discovered some of the very reasons why I chose to make > a new interface.=C2=A0 I could tweak the commit message to mention > alternatives, if that would help. I suppose it wouldn=E2=80=99t help me, but it can=E2=80=99t harm either. S= o if it isn=E2=80=99t too difficult, why not. Max --rbLs3AcreBqFWJWPqXZsuNkXcg23eN9LH-- --ZdWUiVHyyanP6F6jKwFpZHJO6zneu5yju Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl66P/0ACgkQ9AfbAGHV z0BZnwf/TEoa8j+Co9bNtDLNmS2dJKoZEqxD52eDPV7JtKbFOQwTvLkVNxM4t/C/ O/S9smb+GOCbQ5SuZPF4MJeXn0VcAn3s3zyrii69ktcu0y5hLQON7EMhX2oscB8N UWOCykqDlKWJaG7bTj/40lmEmPd4ffB0/IhwUViGjowVoKCOrzy2jYkEyJz+ezO0 Qr+gbm41HqM3YwGo54VPghUQJJ7kraztUs70y1KN1eZ70xvrgqoFTh1BppoQg0J0 jfmszY7FjWlGyYMhAnHDXWa2Rn9sYosCplugOQVeXFlcPBPhsiNqa0aiBVRFjdE3 GIBx2V7pKr9Rv5LgeOrcOMKouYVcXw== =iJfd -----END PGP SIGNATURE----- --ZdWUiVHyyanP6F6jKwFpZHJO6zneu5yju--