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Thu, 27 Feb 2020 14:54:50 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.111]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E5D4089F21; Thu, 27 Feb 2020 14:54:48 +0000 (UTC) Subject: Re: [PATCH] qcow2: Explicit mention of padding bytes To: Eric Blake , qemu-devel@nongnu.org References: <20200227144508.1078501-1-eblake@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: <36d1582d-3b2a-d697-110e-25973e344be1@redhat.com> Date: Thu, 27 Feb 2020 15:54:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200227144508.1078501-1-eblake@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="DduQpZZfcuF7w84cJaD1Uhyf7AfsH855k" 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: kwolf@redhat.com, dplotnikov@virtuozzo.com, vsementsov@virtuozzo.com, 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) --DduQpZZfcuF7w84cJaD1Uhyf7AfsH855k Content-Type: multipart/mixed; boundary="izy467crMbQ3DQiGACCRt2YRfqf5EgklG" --izy467crMbQ3DQiGACCRt2YRfqf5EgklG Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 27.02.20 15:45, Eric Blake wrote: > Although we already covered the need for padding bytes with our > changes in commit 3ae3fcfa, commit 66fcbca5 just added one byte and > relied on the earlier text for implicitly covering 7 padding bytes. > For consistency with other parts of the header, Those other places are about table entries where there is padding to the next entry of the table, though. In addition, for those other places it=E2=80=99s the only mention that they are padded. For the header, there is a whole own section describing the padding, so I don=E2=80=99t quite see the point. > it does not hurt to be > explicit that this version of the header is using padding bytes, and > if we later add other extension fields, we can rework the allocation > of those padding bytes to match those additions. >=20 > Signed-off-by: Eric Blake > --- > docs/interop/qcow2.txt | 2 ++ > 1 file changed, 2 insertions(+) >=20 > diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt > index 5597e244746e..193ac7c5c1af 100644 > --- a/docs/interop/qcow2.txt > +++ b/docs/interop/qcow2.txt > @@ -209,6 +209,8 @@ version 2. > Available compression type values: > 0: zlib >=20 > + 105 - m: Zero padding to round up the header size to the next > + multiple of 8. And if we really want this, I think it might as well be specific, i.e. =E2=80=9C105 - 112=E2=80=9D. We would have to adjust it every time we add = a new field anyway. Max > =3D=3D=3D Header padding =3D=3D=3D >=20 --izy467crMbQ3DQiGACCRt2YRfqf5EgklG-- --DduQpZZfcuF7w84cJaD1Uhyf7AfsH855k Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl5X2DcACgkQ9AfbAGHV z0B3Ygf/RK38wcxBh5btiRU3eUPNU6+CXHLS9lc7AXI1aBcHaQcYHzX3ELAAQ7BQ 3HbKn5WPpfpomnA57jxDb8RSEye2oWzxxHi6UTsQScERoSzco7dSLWO6ye8pZfFU 6xSzdbIosfY6sh+CkNJnFfhNex50d6Wp/Zu6DUgNHO2JS0oJyJe7bE7CyGGUL0hd ry+KEw/EHow0Rlj1O4q4onydVuvw/MgiVYrZoDm6AaQWVtaBo6UqsYnM9wSwK1zL HDVbhoF+JPaSd8Xh5O6BuFA2erhmX4b7cjNFtlWPOQKKELBccSn/CCV+Skk1+JKa uaQ2py909CwSgbQuy+8cFyzfMagkeg== =NGqA -----END PGP SIGNATURE----- --DduQpZZfcuF7w84cJaD1Uhyf7AfsH855k--