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Thu, 1 Aug 2019 19:06:44 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" References: <20190725091900.30542-1-vsementsov@virtuozzo.com> <20190725091900.30542-2-vsementsov@virtuozzo.com> <2a105159-ab90-8f7c-bba9-4cec27e6144c@redhat.com> From: Max Reitz Openpgp: preference=signencrypt 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: Thu, 1 Aug 2019 21:06:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="JuRKQC7MvTWMuu1hJ2IpBMrWdlgdtFK2v" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 01 Aug 2019 19:06:50 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v3 1/9] block: add .bdrv_need_rw_file_child_during_reopen_rw handler 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: "fam@euphon.net" , "kwolf@redhat.com" , "jsnow@redhat.com" , Denis 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) --JuRKQC7MvTWMuu1hJ2IpBMrWdlgdtFK2v Content-Type: multipart/mixed; boundary="j8bFQKcnsDXTVYWLZ2JmcvlZ7hDrLSdgf"; protected-headers="v1" From: Max Reitz To: Vladimir Sementsov-Ogievskiy , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" Cc: "jsnow@redhat.com" , "fam@euphon.net" , "kwolf@redhat.com" , Denis Lunev Message-ID: Subject: Re: [PATCH v3 1/9] block: add .bdrv_need_rw_file_child_during_reopen_rw handler References: <20190725091900.30542-1-vsementsov@virtuozzo.com> <20190725091900.30542-2-vsementsov@virtuozzo.com> <2a105159-ab90-8f7c-bba9-4cec27e6144c@redhat.com> In-Reply-To: --j8bFQKcnsDXTVYWLZ2JmcvlZ7hDrLSdgf Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01.08.19 16:02, Vladimir Sementsov-Ogievskiy wrote: > 31.07.2019 15:09, Max Reitz wrote: [...] >> So -- without having tried, of course -- I think a better design would= >> be to look for bs->file->bs in the ReopenQueue, recursively all of its= >> children, and move all of those entries into a new queue, and then >> invoke bdrv_reopen_multiple() on that one first. >=20 > Why all children recursively? Shouldn't we instead only follow defined > dependencies? > Or it just seems bad to put not full subtree into bdrv_reopen multiple(= ) ? For example, making a node RW without opening its children RW seems wrong. Whenever we reopen a node, we should reopen all of its children, if they are in the queue. >> The question then becomes how to roll back those changes... I don=E2=80= =99t >> know whether just having bdrv_reopen() partially succeed is so bad. >> Otherwise, we=E2=80=99d need a function to translate an existing node'= s state >> into a BdrvReopenQueueEntry so we can thus return to the old state. >=20 > And this rollback may fail too and we are still in partial success stat= e. >=20 > But if we roll-back simple ro->rw reopen it's safe enough: in worst cas= e > file will be rw, but marked ro, so Qemu may have more access rights tha= n > needed but will not use them, this is why I was concentrating around > only ro->rw case.. In practice, this is always so. The =E2=80=9Cchildren need to be reopene= d before parent=E2=80=9D case is always a sign of more permissions being ta= ken; whereas =E2=80=9Cchildren need to be reopened after parent=E2=80=9D is a = sign of permissions being released. What we want to fix now is the former =E2=80=9Creopen children before par= ent=E2=80=9D case. Because this is always a sign of taking more permissions, a partial success/failure state means we always have taken more permissions than we need to. > So, what about go similar way to this patch, i.e. only reopen ro->rw ch= ildren > which we need to be rw, not touching other flags, but check, that in re= open > queue we have this child, and it is going to be reopened RW, and if not= , > return error immediately? If the RO -> RW change for the child is accompanied by other options being changed, the user may find it vital to change these flags along with the RO/RW access. We shouldn=E2=80=99t ignore them. Max --j8bFQKcnsDXTVYWLZ2JmcvlZ7hDrLSdgf-- --JuRKQC7MvTWMuu1hJ2IpBMrWdlgdtFK2v Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1DOEMACgkQ9AfbAGHV z0DOVQf7BMRXeZUlHcHlOt2mwNmzTWjqsu6mIA1a+gmibZncECxsz3XR0JEyF5iR 4zZScArk4AAjNvF4npLKCR4bWwq6ubMjspJmt0MAg06+Gn05iNh7RgsWUheTT49L TcYn+xcS4nSbBcPOm82WCuO2EtXJy48cysynTPq8jhcUJ2stG0F1MM2hSB0dEav+ Vdu50MONRvZiEdxgGlCQCVz/nzo1/6oYyK4U+BtLE9yOgN0EGCUsfQ5gycdl3U8A SeJUf7bHd6ju8/eBjy/MosJku/sC3UOLCUiMPQn6TuZPBGnxEmMfq0n+O1LJcdY8 gQXeQ1ZaPZjAfGA994jGZ4n+ZeIjaQ== =dw3h -----END PGP SIGNATURE----- --JuRKQC7MvTWMuu1hJ2IpBMrWdlgdtFK2v--