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Thu, 24 Oct 2019 09:31:06 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-205.ams2.redhat.com [10.36.117.205]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D6EBA60F8E; Thu, 24 Oct 2019 09:31:04 +0000 (UTC) Subject: Re: [PATCH] blockdev: modify blockdev-change-medium to change non-removable device To: Vladimir Sementsov-Ogievskiy , Denis Plotnikov , "qemu-block@nongnu.org" References: <20191018120950.26849-1-dplotnikov@virtuozzo.com> <2b6cc2fe-5269-71ab-9f0b-1ab36d4dc050@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: <01c37742-2c68-2e49-6011-48d2812a4d91@redhat.com> Date: Thu, 24 Oct 2019 11:31:03 +0200 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 10.5.11.12 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="VMmdMA6WC1Wca2dZZtxCcIYChpNv7BjRr" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 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" , "armbru@redhat.com" , "qemu-devel@nongnu.org" , "dgilbert@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) --VMmdMA6WC1Wca2dZZtxCcIYChpNv7BjRr Content-Type: multipart/mixed; boundary="GCohYTSrD5UIWQeYocED4IJ3MCeK8oKrB" --GCohYTSrD5UIWQeYocED4IJ3MCeK8oKrB Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 23.10.19 16:10, Vladimir Sementsov-Ogievskiy wrote: > 23.10.2019 16:56, Vladimir Sementsov-Ogievskiy wrote: >> 22.10.2019 14:05, Max Reitz wrote: >>> On 21.10.19 08:50, Denis Plotnikov wrote: >>>> >>>> On 18.10.2019 18:02, Max Reitz wrote: >>>>> On 18.10.19 14:09, Denis Plotnikov wrote: >>>>>> The modification is useful to workaround exclusive file access restr= ictions, >>>>>> e.g. to implement VM migration with shared disk stored on a storage = with >>>>>> the exclusive file opening model: a destination VM is started waitin= g for >>>>>> incomming migration with a fake image drive, and later, on the last = migration >>>>>> phase, the fake image file is replaced with the real one. >>>>>> >>>>>> Signed-off-by: Denis Plotnikov >>>>> Isn=E2=80=99t this what we would want to use reopen for? >>>>> >>>>> Max >>>> >>>> Could you please explain what is "use reopen"? >>> >>> I was thinking of using (x-)blockdev-reopen to change the file that is >>> used by the format node (e.g. from a null-co node to a real file); or t= o >>> change the filename of the protocol node. >>> >>> Kevin has pointed out (on IRC) that this will not allow you to change >>> the node that is directly attached to the device. While I don=E2=80=99= t know >>> whether that=E2=80=99s really necessary in this case, if it were indeed >>> necessary, I=E2=80=99d prefer a method to change a guest device=E2=80= =99s @drive option >>> because that seems more natural to me. >>> >>> In contrast, the approach taken in this patch seems not quite right to >>> me, because it overloads the whole blockdev-change-medium command with = a >>> completely new and different implementation based on whether there=E2= =80=99s a >>> removable medium or not. If the implementation is so different (and th= e >>> interface is, too, because in one path you must give @medium whereas th= e >>> other doesn=E2=80=99t evaluate it at all), it should be a new command. >>> >>> I don=E2=80=99t know whether we need a new command at all, though. On = the node >>> level, we have (x-)blockdev-reopen. So assuming we need something to >>> change the link between the guest device and the block layer, I wonder >>> whether there isn=E2=80=99t something similar; specifically, I=E2=80=99= d prefer >>> something to simply change the device=E2=80=99s @drive option. >> >> Ok, assume we can set @drive option with help of improved qom-set. >> But how to create this new blk? blockdev-add don't have 'id' parameter a= nymore >> and don't create blk... >=20 >=20 > Hmm, I see, we have command blockdev-insert-medium(id, node-name). Isn't = it what > we want? blockdev-insert-medium requires that the device be empty, so it would need to be preceded by a blockdev-remove-medium. And then it isn=E2=80=99t= a transaction... Also, it currently is limited (intentionally) to devices with removable media. I suppose all of this could be changed, but basically I don=E2=80=99t see w= hy we wouldn=E2=80=99t use qom-set. (Well, because it=E2=80=99s ugly to call thi= s new functionality from set_drive(), but other than that...) (And I don=E2=80=99t quite know whether there isn=E2=80=99t more to be done= for devices that don=E2=80=99t inherently support removable media than just to swap the= node attached to the BB. Don=E2=80=99t they also need to be drained or somethin= g?) Max --GCohYTSrD5UIWQeYocED4IJ3MCeK8oKrB-- --VMmdMA6WC1Wca2dZZtxCcIYChpNv7BjRr Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl2xb1cACgkQ9AfbAGHV z0DiTQgAmrc4bvna8uYFL4IA5URpTEsAvlOqOG2Hzv8CpLeaKolatFaYytexyGRm w3l75lYcyfqNgvVWDKOxvIrrqJJORSX8L2YoQP9jwyUqsUGIjl7xlB5igVa+pLsk rY1hABM4DkNOgfrmWMd4GZHoTsDVbiI9igzW0cy0bzMmgGfYZQVrSFfpBgl5aqH9 LUFLWothyzZ5x7THCcJnYxSYr/EEFsYY7lu8HlCKdb3Oqn3/HqhXSEtTKEPlV0ry R2MjNDCWkf07mJkm1MKKewf6hzwG3l1LTYvjZIzW1fHfzSAtG3JjYtki2jXmycra 2tMLxjLwG3cd0cLNwb2eRcTuUmoA8A== =uLmF -----END PGP SIGNATURE----- --VMmdMA6WC1Wca2dZZtxCcIYChpNv7BjRr--