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Mon, 9 Sep 2019 08:31:10 +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 4E1DC5C1D8; Mon, 9 Sep 2019 08:31:09 +0000 (UTC) To: Kevin Wolf References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-17-mreitz@redhat.com> <20190905162407.GD4911@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 10:31:07 +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: <20190905162407.GD4911@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PLnIjIH3d5nQLhKtUfA9FXfovVlVPxXAw" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.67]); Mon, 09 Sep 2019 08:31:10 +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) --PLnIjIH3d5nQLhKtUfA9FXfovVlVPxXAw Content-Type: multipart/mixed; boundary="TL2DAdaqMWNBy7coG8aW9kI0hyW46JIOj"; 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> In-Reply-To: <20190905162407.GD4911@localhost.localdomain> --TL2DAdaqMWNBy7coG8aW9kI0hyW46JIOj Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 fl= ush >>>> just bs->file->bs, but in fact all children. >>>> >>>> In any case, the BLKDBG_EVENT() should be emitted on the primary chi= ld, >>>> 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(v= oid *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(BlockDriverStat= e *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(BlockDriverSt= ate *bs) >>>> =20 >>>> /* But don't actually force it to the disk with cache=3Dunsafe= */ >>>> 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(BlockDriverSta= te *bs) >>>> /* Now flush the underlying protocol. It will also have BDRV_= O_NO_FLUSH >>>> * in the case of cache=3Dunsafe, so there are no useless flus= hes. >>>> */ >>>> -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 f= rom parent.. >> >> Good that you remember it, I must have overlooked it (when reading the= >> replies to the previous version). :-) >> >>> Shouldn't we check it? Or we assume that it's always safe to call bdr= v_co_flush on >>> a node? >> >> I think it=E2=80=99s always safe. But checking it seems like a nice t= ouch, yes. >=20 > I'm not sure why we would unconditionally flush all children anyway. Th= e > 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 this= =2E > blkverify implements .bdrv_co_flush, so it's not affected by the change= > anyway, but quorum children will be flushed twice now. >=20 > 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 case= , > I'd rather not do this. >=20 > 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 driver,= > but maybe restricting the recursion to read-only is actually good enoug= h > 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. Max --TL2DAdaqMWNBy7coG8aW9kI0hyW46JIOj-- --PLnIjIH3d5nQLhKtUfA9FXfovVlVPxXAw Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl12DcsACgkQ9AfbAGHV z0CfBAf8COyDHP9cyfupM9PckYBBRmzrPZlKwwPApHcckyXrHv7X/KQOp4rF6hPp Xahr9rKPaKTmdt5iALO0IsTKYpOTpqrbKCLt+8qi2X6dv/rCxqD3VtRaCQpxQYoE ZlFHSFMn5z/1EbEUHQ9hUOYpbUFkytxSwBmnuTzm59IPNuSjR6C+v9AqeDPcVH1V oIEQeDuZSN3/XmsM/HJ9GnLc/ZCHhnBi5pzdoUCmNioeeb9EeMCzmwk9Ttpni4+c q5bPLWgp8QXFT4WrPDD3I2M7FVXuCJvXRQw8ZpXZuN7x8gnM4CauIkhcOW6wgpFZ ES2atxrzNUDbOXjYqromPcmHhDjPmQ== =KxSh -----END PGP SIGNATURE----- --PLnIjIH3d5nQLhKtUfA9FXfovVlVPxXAw--