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Tue, 5 Nov 2019 12:05:20 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-89.ams2.redhat.com [10.36.117.89]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2DFEF5D72B; Tue, 5 Nov 2019 12:05:14 +0000 (UTC) Subject: Re: [RFC PATCH v2 22/26] qcow2: Add subcluster support to handle_alloc_space() To: Alberto Garcia , qemu-devel@nongnu.org References: 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: <205ff5db-cbaf-03a4-8df4-f505bc63ecaa@redhat.com> Date: Tue, 5 Nov 2019 13:05:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Hz8yIfvBPjkkR1rZwe9vlyLJg8F7tgvtR" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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 , Anton Nefedov , qemu-block@nongnu.org, Vladimir Sementsov-Ogievskiy , "Denis V . Lunev" 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) --Hz8yIfvBPjkkR1rZwe9vlyLJg8F7tgvtR Content-Type: multipart/mixed; boundary="H0EtTGy2Et5lhXmLNgyuFxiHRR8yODb6J" --H0EtTGy2Et5lhXmLNgyuFxiHRR8yODb6J Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 26.10.19 23:25, Alberto Garcia wrote: > The bdrv_co_pwrite_zeroes() call here fills complete clusters with > zeroes, but it can happen that some subclusters are not part of the > write request or the copy-on-write. This patch makes sure that only > the affected subclusters are overwritten. >=20 > A potential improvement would be to also fill with zeroes the other > subclusters if we can guarantee that we are not overwriting existing > data. However this would waste more disk space, so we should first > evaluate if it's really worth doing. >=20 > Signed-off-by: Alberto Garcia > --- > block/qcow2.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) >=20 > diff --git a/block/qcow2.c b/block/qcow2.c > index 0261e87709..01322ca449 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -2304,6 +2304,9 @@ static int handle_alloc_space(BlockDriverState *bs,= QCowL2Meta *l2meta) > =20 > for (m =3D l2meta; m !=3D NULL; m =3D m->next) { > int ret; > + uint64_t start_offset =3D m->alloc_offset + m->cow_start.offset; > + uint64_t nb_bytes =3D m->cow_end.offset + m->cow_end.nb_bytes - > + m->cow_start.offset; It might be more honest to make nb_bytes an unsigned. (There shouldn=E2=80= =99t be any overflows here, because the total size is limited to INT64_MAX by handle_alloc().) Max > if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) { > continue; --H0EtTGy2Et5lhXmLNgyuFxiHRR8yODb6J-- --Hz8yIfvBPjkkR1rZwe9vlyLJg8F7tgvtR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl3BZXgACgkQ9AfbAGHV z0ArvQgAqO4r+OiEITYVz0hXv50UmB4OqSVScs8xaMjavUQeiKof+5xCQ21PdpSH 8oaJTUZtk25Tjg7G9m/XXwa4YKmm4KKQHK0kXXUiXuYSZoe+DYHOxuiWFzAjp+pt cm4AdzyDkFwNlMl3YMpmgOIOrqPBXdXK1kkSckm6AhYF8kxdo31ri4xGY3dzYydg XxZJIWiF6PyZCmRvkt86GlJFINBoH2k+lq24j2sgGPnQaDDLcmobMuVK3FYTxmcc V4AiKcfpkYo/ymAGTgXpikLO69g6EFv5NL9BNPFf5JGt+Sq+chCAkWlGMVTmr13w 2q05L8Zwjaev9PuXnahGR7EfNvubjQ== =uxpq -----END PGP SIGNATURE----- --Hz8yIfvBPjkkR1rZwe9vlyLJg8F7tgvtR--