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Tue, 14 Apr 2020 10:13:14 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-186.ams2.redhat.com [10.36.114.186]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3DA6010016DA; Tue, 14 Apr 2020 10:13:11 +0000 (UTC) Subject: Re: [PATCH v4 20/30] qcow2: Add subcluster support to discard_in_l2_slice() To: Alberto Garcia , qemu-devel@nongnu.org References: <99b45e3beb4a38b17eb50fcde1e09cdefdb99724.1584468723.git.berto@igalia.com> <4b3b1ef4-2f8b-b16f-3c48-2ba6137763e4@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: <58cf9489-057d-429a-8445-cfdffadfa4af@redhat.com> Date: Tue, 14 Apr 2020 12:13:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PzX1DbnhCrEYQUD0b3DWgzXplC7ZKAP5F" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 207.211.31.120 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: 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) --PzX1DbnhCrEYQUD0b3DWgzXplC7ZKAP5F Content-Type: multipart/mixed; boundary="OgAnbGdHtoUU1o7iYoXCBEbiMDcSi80Xz" --OgAnbGdHtoUU1o7iYoXCBEbiMDcSi80Xz Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 10.04.20 14:47, Alberto Garcia wrote: > On Thu 09 Apr 2020 12:05:12 PM CEST, Max Reitz wrote: >>> switch (qcow2_get_cluster_type(bs, old_l2_entry)) { >>> case QCOW2_CLUSTER_UNALLOCATED: >>> - if (full_discard || !bs->backing) { >>> + if (full_discard) { >>> + /* If the image has extended L2 entries we can only >>> + * skip this operation if the L2 bitmap is zero. */ >>> + uint64_t bitmap =3D has_subclusters(s) ? >>> + get_l2_bitmap(s, l2_slice, l2_index + i) : 0; >> >> Isn=E2=80=99t this bitmap only valid for standard clusters? In this cas= e, the >> whole cluster is unallocated, so the bitmap shouldn=E2=80=99t be relevan= t, >> AFAIU. >=20 > I'm not sure if I follow you. >=20 > An unallocated cluster can still have QCOW_OFLAG_SUB_ZERO set in some of > its subclusters. Those read as zeroes and the rest go to the backing > file. Hm, right, this is the only way to have non-preallocated zero clusters after all. I suppose I read the spec wrong and assumed somehow that unallocated clusters don=E2=80=99t use =E2=80=9Cstandard cluster descriptors=E2=80=9D, = so their bitmap usage would be undefined. Don=E2=80=99t know how that happened. > After a full discard all subclusters should be completely deallocated so > those bits should be cleared. >=20 > If the bitmap is already 0 (the whole cluster is already unallocated) or > if the image does not have extended L2 entries (which also means that > the whole cluster is already unallocated) then we can skip the discard. Yep, seems right. Reviewed-by: Max Reitz --OgAnbGdHtoUU1o7iYoXCBEbiMDcSi80Xz-- --PzX1DbnhCrEYQUD0b3DWgzXplC7ZKAP5F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6VjLUACgkQ9AfbAGHV z0AmHAf/Qm/cktZ7C4ETFe3osU2oHgTs1oQvfXFxt39VBOdFetsXhSXm1wwOOBUL BDzxBEtFICOQ+uNSo7+BYv0P+V2lRMVtKouTDvY5+eWwCjxJHxsK9V2R6keMzrZr FURdr60mXKElOBpMJIldKbHOzc+NmhSaBcfEYGyIeUGpsezsdXAurjAw6sb5dPaP lKKjriKF7pIdaOMjEcJ44i46vRdS4poK0Gs/Z8H9FVMnSivEdP3e0UWHxw5SzANF NJ/baEm/aGQbd2YPX8wLOwm9t2fpRPcH2j+5bADdgcNx7o2/mazQAlOXoUCSD0HG avYPaXlLZVCz0X8lBUDWh2hlwwlNrg== =y6GW -----END PGP SIGNATURE----- --PzX1DbnhCrEYQUD0b3DWgzXplC7ZKAP5F--