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Mon, 17 Feb 2020 14:40:59 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-191.ams2.redhat.com [10.36.117.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EDB3A10001AE; Mon, 17 Feb 2020 14:40:56 +0000 (UTC) Subject: Re: [PATCH v2 03/33] block: Add BdrvChildRole To: Alberto Garcia , qemu-block@nongnu.org References: <20200204170848.614480-1-mreitz@redhat.com> <20200204170848.614480-4-mreitz@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: Date: Mon, 17 Feb 2020 15:40:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 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="bAxUUpmp4cC8XZV8zYGBKfwMlj5FOezJH" 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 , Vladimir Sementsov-Ogievskiy , 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) --bAxUUpmp4cC8XZV8zYGBKfwMlj5FOezJH Content-Type: multipart/mixed; boundary="3D4XAEo0K6xVyBDNujvb5OMbgg0vDFXk8" --3D4XAEo0K6xVyBDNujvb5OMbgg0vDFXk8 Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 11.02.20 16:41, Alberto Garcia wrote: > On Tue 04 Feb 2020 06:08:18 PM CET, Max Reitz wrote: >> + /* Child to COW from (backing child) */ >> + BDRV_CHILD_COW =3D (1 << 3), >=20 > Without the comment in brackets I'm not sure that I would have > understood that this is meant for backing files. I put it in brackets because bs->backing isn=92t always such a child (for filters it isn=92t). That=92s also the reason why I prefer to stress the COW aspect. > This is the "child that contains the data that is not allocated in the > parent", or something like that, right? Hm, so I suppose the problem is that I didn=92t describe in which event the COW is to occur. (I didn=92t because we only have one kind of COW in the block layer, namely for backing chains.) So maybe =93Child from which to read all data that isn=92t allocated in the parent (backing child); such data may be copied to the parent by means of COW or COR=94? (The problem I see with this description is that it is kind of a tautology, because =93allocation=94 is in turn defined by differentiating between layers of a backing chain, i.e. this layer and that backing/COW child we=92re talking about here.) Max --3D4XAEo0K6xVyBDNujvb5OMbgg0vDFXk8-- --bAxUUpmp4cC8XZV8zYGBKfwMlj5FOezJH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl5KpfcACgkQ9AfbAGHV z0DEtggAsFlQMtEU09v7rRJlyADjKbUxeUaQ/bVP4mjx2LQ8nxhBhGexDre4F6vQ hJ5KRoUrR3FTFGx9kFgXblEoiFuEK2AUlHhxHJkaGdpX/JFJS8jG+5Olp6MKkBpp svCpcKJl3M8SktwkcTVSUOvLDAyjIIVsQzdHUh+4IaXTW4PEemnPJdTL9Nj9Yv8B t9HK7oetvJuG0x/NWZr6HCQkSb1fevQ9kk9WOBPJh03IqAEzVlJfr6wLlwCKxvQ9 kzPrvuKjaAJs2YwtG3HQED0oKvrdrYs8Me9Nk2yhLSNpvUAJ24iPGQHv6kas3FNT 3vxAptuwZLD564+4CtwtpdFyDX78ZQ== =WE9A -----END PGP SIGNATURE----- --bAxUUpmp4cC8XZV8zYGBKfwMlj5FOezJH--