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Mon, 9 Sep 2019 14:08:30 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-116-179.ams2.redhat.com [10.36.116.179]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1D7F060BF7; Mon, 9 Sep 2019 14:08:26 +0000 (UTC) To: Kevin Wolf References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-15-mreitz@redhat.com> <20190905140547.GC4911@localhost.localdomain> <20190909095547.GB17606@localhost.localdomain> From: Max Reitz Openpgp: preference=signencrypt 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: <30c5d55f-b3ef-4a52-883d-93059a76b383@redhat.com> Date: Mon, 9 Sep 2019 16:08:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190909095547.GB17606@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="soSF6sG3VGuA5awFVzPlmyt3tdM6TLfFL" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 09 Sep 2019 14:08:30 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v6 14/42] block: Use CAFs when working with backing chains 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: Vladimir Sementsov-Ogievskiy , 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) --soSF6sG3VGuA5awFVzPlmyt3tdM6TLfFL Content-Type: multipart/mixed; boundary="mxF51ywizOJnWMJIvrg1wZPVObRwW379K"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy Message-ID: <30c5d55f-b3ef-4a52-883d-93059a76b383@redhat.com> Subject: Re: [PATCH v6 14/42] block: Use CAFs when working with backing chains References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-15-mreitz@redhat.com> <20190905140547.GC4911@localhost.localdomain> <20190909095547.GB17606@localhost.localdomain> In-Reply-To: <20190909095547.GB17606@localhost.localdomain> --mxF51ywizOJnWMJIvrg1wZPVObRwW379K Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 09.09.19 11:55, Kevin Wolf wrote: > Am 09.09.2019 um 10:25 hat Max Reitz geschrieben: >> On 05.09.19 16:05, Kevin Wolf wrote: >>> Am 09.08.2019 um 18:13 hat Max Reitz geschrieben: >>>> Use child access functions when iterating through backing chains so >>>> filters do not break the chain. >>>> >>>> Signed-off-by: Max Reitz >>>> --- >>>> block.c | 40 ++++++++++++++++++++++++++++------------ >>>> 1 file changed, 28 insertions(+), 12 deletions(-) >>>> >>>> diff --git a/block.c b/block.c >>>> index 86b84bea21..42abbaf0ba 100644 >>>> --- a/block.c >>>> +++ b/block.c >>>> @@ -4376,7 +4376,8 @@ int bdrv_change_backing_file(BlockDriverState = *bs, >>>> } >>>> =20 >>>> /* >>>> - * Finds the image layer in the chain that has 'bs' as its backing = file. >>>> + * Finds the image layer in the chain that has 'bs' (or a filter on= >>>> + * top of it) as its backing file. >>>> * >>>> * active is the current topmost image. >>>> * >>>> @@ -4388,11 +4389,18 @@ int bdrv_change_backing_file(BlockDriverStat= e *bs, >>>> BlockDriverState *bdrv_find_overlay(BlockDriverState *active, >>>> BlockDriverState *bs) >>>> { >>>> - while (active && bs !=3D backing_bs(active)) { >>>> - active =3D backing_bs(active); >>>> + bs =3D bdrv_skip_rw_filters(bs); >>>> + active =3D bdrv_skip_rw_filters(active); >>> >>> This does more than the commit message says. In addition to iterating= >>> through filters instead of stopping, it also changes the semantics of= >>> the function to return the next non-filter on top of bs instead of th= e >>> next node. >> >> Which is to say the overlay. >> >> (I think we only ever use =E2=80=9Coverlay=E2=80=9D in the COW sense.)= >=20 > I think we do, but so far also only ever for immediate COW childs, not > for skipping through intermediate node. Yes, because it=E2=80=99s broken so far. >>> The block jobs seem to use it only for bdrv_is_allocated_above(), whi= ch >>> should return the same thing in both cases, so the behaviour stays th= e >>> same. qmp_block_commit() will check op blockers on a different node n= ow, >>> which could be a fix or a bug, I can't tell offhand. Probably the >>> blocking doesn't really work anyway. >> >> You mean that the op blocker could have been on a block job filter nod= e >> before? I think that=E2=80=98s pretty much the point of this fix; tha= t that >> doesn=E2=80=99t make sense. (We didn=E2=80=99t have mirror_top_bs and= the like at >> 058223a6e3b.) >=20 > On the off chance that the op blocker actually works, it can't be a job= > filter. I was thinking more of throttling, blkdebug etc. Well, that=E2=80=99s just broken altogether right now. >>> All of this should be mentioned in the commit message at least. Maybe= >>> it's also worth splitting in two patches. >> >> I don=E2=80=99t know. The function was written when there were no fil= ters. >=20 > I doubt it. blkdebug is a really old filter. >=20 >> This change would have been a no-op then. The fact that it isn=E2=80=99= t to me >> just means that introducing filters broke it. >> >> So I don=E2=80=99t know what I would write. Maybe =E2=80=9Cbdrv_find_= overlay() now >> actually finds the overlay, that is, it will not return a filter node.= >> This is the behavior that all callers expect (because they work on COW= >> backing chains).=E2=80=9D >=20 > Maybe just something like "In addition, filter nodes are not returned a= s > overlays any more. Instead, the first non-filter node on top of bs is > considered the overlay now."? Isn=E2=80=99t that basically the same? :-) Max --mxF51ywizOJnWMJIvrg1wZPVObRwW379K-- --soSF6sG3VGuA5awFVzPlmyt3tdM6TLfFL Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl12XNcACgkQ9AfbAGHV z0DMMwf+PAlpzmBOrPKi/WL9m5kIT2Qo9zr0isTmt21IyagrZmmS6tyTr8GrwVYP vfkLJMIuPrtbVe12bCeeXdcVZz5lXHfIZtovi9VwtIBzvXUCK63RfVGvXqhQf74c eC86uFOZkHUwujVG4r6R1oTGRQiKBJI/0qrF3hHvQ5t9G4isqRV2+JVqUnynMLUq oMF/xrSB7U7xa2b2Znw7FAlkcwdFIjvZYVnwKARwqG7rgIdXU2qq5YZmKcIVouWq gfx8FXP2dR1LVKN0gA2sf8ANA38E9dJCkTf6xWYbHf8Yx5id86jpBejIuZtATvSg 7gDiMIin0GN4dX7UiBcWWf0ZCR3xlg== =thB6 -----END PGP SIGNATURE----- --soSF6sG3VGuA5awFVzPlmyt3tdM6TLfFL--