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Mon, 9 Sep 2019 14:16:04 +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 DB1D160BE2; Mon, 9 Sep 2019 14:16:01 +0000 (UTC) To: Kevin Wolf References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-17-mreitz@redhat.com> <20190905162407.GD4911@localhost.localdomain> <20190909100147.GC17606@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: Date: Mon, 9 Sep 2019 16:15:59 +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: <20190909100147.GC17606@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Nt4jewN1rFFqeSQhFJPZVGG1Ouqr3TISY" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.69]); Mon, 09 Sep 2019 14:16:04 +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 16/42] block: Flush all children in generic code 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) --Nt4jewN1rFFqeSQhFJPZVGG1Ouqr3TISY Content-Type: multipart/mixed; boundary="26x3pPfWbISwqCNzhi0bgr8xP5c7FRKx8"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" Message-ID: Subject: Re: [PATCH v6 16/42] block: Flush all children in generic code References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-17-mreitz@redhat.com> <20190905162407.GD4911@localhost.localdomain> <20190909100147.GC17606@localhost.localdomain> In-Reply-To: <20190909100147.GC17606@localhost.localdomain> --26x3pPfWbISwqCNzhi0bgr8xP5c7FRKx8 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 09.09.19 12:01, Kevin Wolf wrote: > Am 09.09.2019 um 10:31 hat Max Reitz geschrieben: >> On 05.09.19 18:24, Kevin Wolf wrote: >>> Am 12.08.2019 um 14:58 hat Max Reitz geschrieben: >>>> On 10.08.19 17:36, Vladimir Sementsov-Ogievskiy wrote: >>>>> 09.08.2019 19:13, Max Reitz wrote: >>>>>> If the driver does not support .bdrv_co_flush() so bdrv_co_flush()= >>>>>> itself has to flush the children of the given node, it should not = flush >>>>>> just bs->file->bs, but in fact all children. >>>>>> >>>>>> In any case, the BLKDBG_EVENT() should be emitted on the primary c= hild, >>>>>> because that is where a blkdebug node would be if there is any. >>>>>> >>>>>> Suggested-by: Vladimir Sementsov-Ogievskiy >>>>>> Signed-off-by: Max Reitz >>>>>> --- >>>>>> block/io.c | 23 +++++++++++++++++------ >>>>>> 1 file changed, 17 insertions(+), 6 deletions(-) >>>>>> >>>>>> diff --git a/block/io.c b/block/io.c >>>>>> index c5a8e3e6a3..bcc770d336 100644 >>>>>> --- a/block/io.c >>>>>> +++ b/block/io.c >>>>>> @@ -2572,6 +2572,8 @@ static void coroutine_fn bdrv_flush_co_entry= (void *opaque) >>>>>> =20 >>>>>> int coroutine_fn bdrv_co_flush(BlockDriverState *bs) >>>>>> { >>>>>> + BdrvChild *primary_child =3D bdrv_primary_child(bs); >>>>>> + BdrvChild *child; >>>>>> int current_gen; >>>>>> int ret =3D 0; >>>>>> =20 >>>>>> @@ -2601,7 +2603,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverSt= ate *bs) >>>>>> } >>>>>> =20 >>>>>> /* Write back cached data to the OS even with cache=3Dunsafe= */ >>>>>> - BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS); >>>>>> + BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_OS); >>>>>> if (bs->drv->bdrv_co_flush_to_os) { >>>>>> ret =3D bs->drv->bdrv_co_flush_to_os(bs); >>>>>> if (ret < 0) { >>>>>> @@ -2611,15 +2613,15 @@ int coroutine_fn bdrv_co_flush(BlockDriver= State *bs) >>>>>> =20 >>>>>> /* But don't actually force it to the disk with cache=3Dunsa= fe */ >>>>>> if (bs->open_flags & BDRV_O_NO_FLUSH) { >>>>>> - goto flush_parent; >>>>>> + goto flush_children; >>>>>> } >>>>>> =20 >>>>>> /* Check if we really need to flush anything */ >>>>>> if (bs->flushed_gen =3D=3D current_gen) { >>>>>> - goto flush_parent; >>>>>> + goto flush_children; >>>>>> } >>>>>> =20 >>>>>> - BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK); >>>>>> + BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_DISK); >>>>>> if (!bs->drv) { >>>>>> /* bs->drv->bdrv_co_flush() might have ejected the BDS >>>>>> * (even in case of apparent success) */ >>>>>> @@ -2663,8 +2665,17 @@ int coroutine_fn bdrv_co_flush(BlockDriverS= tate *bs) >>>>>> /* Now flush the underlying protocol. It will also have BDR= V_O_NO_FLUSH >>>>>> * in the case of cache=3Dunsafe, so there are no useless fl= ushes. >>>>>> */ >>>>>> -flush_parent: >>>>>> - ret =3D bs->file ? bdrv_co_flush(bs->file->bs) : 0; >>>>>> +flush_children: >>>>>> + ret =3D 0; > + QLIST_FOREACH(child, &bs->children, next) {= >>>>>> + int this_child_ret; >>>>>> + >>>>>> + this_child_ret =3D bdrv_co_flush(child->bs); >>>>>> + if (!ret) { >>>>>> + ret =3D this_child_ret; >>>>>> + } >>>>>> + } >>>>> >>>>> Hmm, you said that we want to flush only children with write-access= from parent.. >>>> >>>> Good that you remember it, I must have overlooked it (when reading t= he >>>> replies to the previous version). :-) >>>> >>>>> Shouldn't we check it? Or we assume that it's always safe to call b= drv_co_flush on >>>>> a node? >>>> >>>> I think it=E2=80=99s always safe. But checking it seems like a nice= touch, yes. >>> >>> I'm not sure why we would unconditionally flush all children anyway. = The >>> only drivers I can think of that really need to flush more than one >>> child are blkverify and quorum, and both of them already implement th= is. >>> blkverify implements .bdrv_co_flush, so it's not affected by the chan= ge >>> anyway, but quorum children will be flushed twice now. >>> >>> But more than this, I'm worried about the overhead of needlessly >>> recursing through the whole backing chain and calling flush on every >>> node there. Maybe bs->write_gen saves us so that at least this doesn= 't >>> result in an fdatasync() call for each, but still... Without a use ca= se, >>> I'd rather not do this. >>> >>> Oh, well, after having written all of this, I see that qcow2 with an >>> external data file is buggy... This could be fixed in the qcow2 drive= r, >>> but maybe restricting the recursion to read-only is actually good eno= ugh >>> then. Can you mention this case in the commit message and maybe build= a >>> test for it? >> >> And I should thus probably drop vmdk=E2=80=99s .bdrv_co_flush_to_disk(= ) >> implementation. >> >> I will indeed try to write a test, but to be completely honest, I feel= >> like this series is long enough. >=20 > I guess I could already merge patch 1 to give you space for another tes= t > patch. ;-) Don=E2=80=99t forget the mirror-top patch. And AFAIR, there was some com= ment from Vladimir that also required an additional patch. So it would need to be three! (Or I just start squashing from the back?) Max --26x3pPfWbISwqCNzhi0bgr8xP5c7FRKx8-- --Nt4jewN1rFFqeSQhFJPZVGG1Ouqr3TISY Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl12Xp8ACgkQ9AfbAGHV z0BiCgf6AolUlNgvWp1zT6dLVUww2V9aQzlLaGhZEC2e61rXKpXX3vAOoGQn3DPm fCAPIT1d+/Cm4MWmTpF9nlvK4FmtYiN7Og4C3BqKQ53zseR9mo24aSqgR8izjQfH ONWsBPGuI2p1hU6A7Bvf525rMJ0jAXhwOqlsu0eUo3oJAAyBOHq1IPe04j5zEWIq OA+IMex8aiRJ43UdLDH6mg1P1bpLQKWq2TmQgWg5hiRC+yTIZ99CdJD/xW3Gxa1D QXsu/j5OjOOibr9C9VMAwI3C4CHRTFyFjIG+YthvSlmj7Z42la6iscxovjEP/IHo e/N/iYo/QALNovKTllNz+OSPfqDlzw== =v8hJ -----END PGP SIGNATURE----- --Nt4jewN1rFFqeSQhFJPZVGG1Ouqr3TISY--