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Wed, 29 Apr 2020 07:58:07 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-113-19.ams2.redhat.com [10.36.113.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0FFBE600DB; Wed, 29 Apr 2020 07:58:05 +0000 (UTC) Subject: Re: [PATCH 4/4] block: Use blk_make_empty() after commits To: Eric Blake , qemu-block@nongnu.org References: <20200428132629.796753-1-mreitz@redhat.com> <20200428132629.796753-5-mreitz@redhat.com> <0fb5d21f-4075-8c6a-0105-01fc60acaecf@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: <5b22a747-c00e-02a2-17fb-652d1eaea453@redhat.com> Date: Wed, 29 Apr 2020 09:58:04 +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: <0fb5d21f-4075-8c6a-0105-01fc60acaecf@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="m9wEpVvEhjEC9nfuOHA6DIecCsv4wjmdg" 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 = 2020/04/29 00:53:13 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: Kevin Wolf , qemu-devel@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) --m9wEpVvEhjEC9nfuOHA6DIecCsv4wjmdg Content-Type: multipart/mixed; boundary="gHhCvHdmBrzcHjs1cm9BoxkpDCHrmINOE" --gHhCvHdmBrzcHjs1cm9BoxkpDCHrmINOE Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 28.04.20 16:07, Eric Blake wrote: > On 4/28/20 8:26 AM, Max Reitz wrote: >> bdrv_commit() already has a BlockBackend pointing to the BDS that we >> want to empty, it just has the wrong permissions. >> >> qemu-img commit has no BlockBackend pointing to the old backing file >> yet, but introducing one is simple. >> >> After this commit, bdrv_make_empty() is the only remaining caller of >> BlockDriver.bdrv_make_empty(). >> >> Signed-off-by: Max Reitz >> --- >> =C2=A0 block/commit.c |=C2=A0 8 +++++++- >> =C2=A0 qemu-img.c=C2=A0=C2=A0=C2=A0=C2=A0 | 19 ++++++++++++++----- >> =C2=A0 2 files changed, 21 insertions(+), 6 deletions(-) >> >> diff --git a/block/commit.c b/block/commit.c >> index 8e672799af..24720ba67d 100644 >> --- a/block/commit.c >> +++ b/block/commit.c >> @@ -493,10 +493,16 @@ int bdrv_commit(BlockDriverState *bs) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (drv->bdrv_make_empty) { >=20 > This 'if' is still a bit awkward. Do all filter drivers set this > function, or will bdrv_make_empty() automatically take care of looking > through filters?=C2=A0 Should this be a check of a supported_ variable > instead (similar to how Kevin just added supported_truncate_flags)? >=20 >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D drv->bdrv_make_empty= (bs); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D blk_set_perm(src, BL= K_PERM_WRITE, BLK_PERM_ALL, NULL); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret < 0) { >> =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 goto ro_cleanup; >> =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 ret =3D blk_make_empty(src, = NULL); >=20 > So, if the driver lacks the callback, you miss calling blk_make_empty() > even if it would have done something. We can=E2=80=99t just call blk_make_empty() and then special case -ENOTSUP = here, though, because the BB doesn=E2=80=99t have a WRITE permission beforehand. = So we have to take that permission before we can call blk_make_empty(). But taking the permission can fail, and then we kind of have to report the -EPERM, even though the BlockDriver may not support emptying anyway. I suppose if we just have to take the WRITE_UNCHANGED permission, though, we can assume that that=E2=80=99s basically always allowed, so it shouldn=E2=80=99t be that much of a problem there. Max >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret < 0) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto= ro_cleanup; >> +=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 blk_flush(src); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 diff --git a/qemu-img.c b/qemu-img.c >> index 821cbf610e..a5e8659867 100644 >> --- a/qemu-img.c >> +++ b/qemu-img.c >> @@ -1065,11 +1065,20 @@ static int img_commit(int argc, char **argv) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto unref_backin= g; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 -=C2=A0=C2=A0=C2=A0 if (!drop && bs->drv->bdrv_make_empty) { >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D bs->drv->bdrv_make_e= mpty(bs); >=20 > Old code: if the driver had the callback, use it. >=20 >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret) { >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 erro= r_setg_errno(&local_err, -ret, "Could not empty %s", >> -=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 filename); >> +=C2=A0=C2=A0=C2=A0 if (!drop) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BlockBackend *old_backing_bl= k; >> + >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 old_backing_blk =3D blk_new_= with_bs(bs, BLK_PERM_WRITE, >> BLK_PERM_ALL, >> +=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 &local_err); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!old_backing_blk) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto= unref_backing; >> +=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 ret =3D blk_make_empty(old_b= acking_blk, &local_err); >=20 > New code: Call blk_make_empty() whether or not driver has the callback, > then deal with the fallout. >=20 >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 blk_unref(old_backing_blk); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret =3D=3D -ENOTSUP) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 erro= r_free(local_err); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 loca= l_err =3D NULL; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else if (ret < 0) { >> =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 goto unref_backing; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >=20 > But this actually looks smarter than the commit case. >=20 --gHhCvHdmBrzcHjs1cm9BoxkpDCHrmINOE-- --m9wEpVvEhjEC9nfuOHA6DIecCsv4wjmdg Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6pM4wACgkQ9AfbAGHV z0DQAAf/V2Wqlar1KUiDrPKrhCio3YNBB/nrDnHMxN4whnAqmUhRN8bnDpJ02xg/ 2lUOxCLiwI0+ELM1Hnve19dqt6/ac8smR/PBCvyh9XhuIcZZUyp1Qye1bCtuCuGP VlnO8OLrAVA5QE7qAXeqywFuGS2+pvdF7Cd7sIR2u0ifqt3SsX5Rmy1v/BuhyECW sopaxLybQZgKTG8Jl2RPAuxx9OlHZgqfUuaVVPxvGf49kcD6sIqDsJba/OWY5fc8 nRw4xzogpNtg9KhIDvBPg/aSx9h53hUYBi+CTqMEf1gSmrl2goTcgYpQan90dWCr 6zj19BUsW1+Gta5vB5da3qSAG2+aSQ== =+Je3 -----END PGP SIGNATURE----- --m9wEpVvEhjEC9nfuOHA6DIecCsv4wjmdg--