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Wed, 29 Apr 2020 08:01:41 +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 4781A60BEC; Wed, 29 Apr 2020 08:01:40 +0000 (UTC) Subject: Re: [PATCH 4/4] block: Use blk_make_empty() after commits To: Kevin Wolf References: <20200428132629.796753-1-mreitz@redhat.com> <20200428132629.796753-5-mreitz@redhat.com> <20200428150311.GK5789@linux.fritz.box> 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: Wed, 29 Apr 2020 10:01:38 +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: <20200428150311.GK5789@linux.fritz.box> 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="FDPssQ5QjHaxlKLtzuK1aAluHKhSuGXDs" 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 = 2020/04/29 01:42:37 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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: 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) --FDPssQ5QjHaxlKLtzuK1aAluHKhSuGXDs Content-Type: multipart/mixed; boundary="2qiUkxfNXlwQxCbycLfYCR1ydz37Pe1Md" --2qiUkxfNXlwQxCbycLfYCR1ydz37Pe1Md Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 28.04.20 17:03, Kevin Wolf wrote: > Am 28.04.2020 um 15:26 hat Max Reitz geschrieben: >> 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 >> --- >> block/commit.c | 8 +++++++- >> qemu-img.c | 19 ++++++++++++++----- >> 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) >> } >> =20 >> if (drv->bdrv_make_empty) { >> - ret =3D drv->bdrv_make_empty(bs); >> + ret =3D blk_set_perm(src, BLK_PERM_WRITE, BLK_PERM_ALL, NULL); >=20 > This is very likely to fail because the common case is that the source > node is attached to a guest device that doesn't share writes. > (qemu-iotests 131 and 274 catch this.) >=20 > So I think after my theoretical comment in patch 1, this is the > practical reason why we need WRITE_UNCHANGED rather than WRITE. >=20 > Also, why don't you take this permission from the start so that we would > error out right away rather than failing after waiting for the all the > data to be copied? Because we only need to take it when the BlockDriver actually supports bdrv_make_empty(), so I thought I=E2=80=99d put it here where we have the c= heck anyway. However, yes, when we take WRITE_UNCHANGED, we might as well take it unconditionally from the start. (And then call blk_make_empty() unconditionally here, too, and let it figure out -ENOTSUP, like Eric noted.= ) >> if (ret < 0) { >> goto ro_cleanup; >> } >> + >> + ret =3D blk_make_empty(src, NULL); >> + if (ret < 0) { >> + goto ro_cleanup; >> + } >> + >> blk_flush(src); >> } >> =20 >> 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) >> goto unref_backing; >> } >> =20 >> - if (!drop && bs->drv->bdrv_make_empty) { >> - ret =3D bs->drv->bdrv_make_empty(bs); >> - if (ret) { >> - error_setg_errno(&local_err, -ret, "Could not empty %s", >> - filename); >> + if (!drop) { >> + BlockBackend *old_backing_blk; >> + >> + old_backing_blk =3D blk_new_with_bs(bs, BLK_PERM_WRITE, BLK_PER= M_ALL, >> + &local_err); >=20 > Oh, you actually depend on another series that you didn't mention in > the cover letter. Well, yes. I didn=E2=80=99t really realize because I just based it on my block-next... Max --2qiUkxfNXlwQxCbycLfYCR1ydz37Pe1Md-- --FDPssQ5QjHaxlKLtzuK1aAluHKhSuGXDs Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6pNGIACgkQ9AfbAGHV z0AT1gf/bqRykFw8IRuIZPA7VzaTGV61KscNPWx6kDMmUoT4d+O66w88vKi2+BZj EmU+iXK6t+VINcbY5i0/vQbROrrxl0bJGr7IaVkJfCDCZ48BskH/AbJXIdeYLPDJ ph3xGGMkqR2XOEMQmksVF/mXSdzNKKzLuDLT7PLmHiuoFJ9OCG7mXqschB29zX/l JbWdAli0w5qm9oGwkBguKYZgUpUGK53yFvfg0dwB2t4u3QiKxYG3UgUof/x2/GEw FniixzJHFFeBnGHQ8tO6SVg7ET0UpPYp4pfG4BtGxy4mDepg6OTz8x18UaS3tl+o RMekcqMu9RN5HT/3cpLPEQ9dflmX8A== =D9i3 -----END PGP SIGNATURE----- --FDPssQ5QjHaxlKLtzuK1aAluHKhSuGXDs--