From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60285) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YgYaP-0002im-1G for qemu-devel@nongnu.org; Fri, 10 Apr 2015 09:03:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YgYaO-00051O-1u for qemu-devel@nongnu.org; Fri, 10 Apr 2015 09:03:04 -0400 Date: Fri, 10 Apr 2015 15:02:52 +0200 From: Kevin Wolf Message-ID: <20150410130252.GC4288@noname.redhat.com> References: <20150402132857.GA26513@igalia.com> <20150409103928.GB2783@stefanha-thinkpad.redhat.com> <20150409124000.GA2500@igalia.com> <20150410095623.GB23555@stefanha-thinkpad.redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="UlVJffcvxoiEqYs2" Content-Disposition: inline In-Reply-To: <20150410095623.GB23555@stefanha-thinkpad.redhat.com> Subject: Re: [Qemu-devel] [Qemu-block] [RFC] Intermediate block mirroring List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Alberto Garcia , qemu-devel@nongnu.org, qemu-block@nongnu.org --UlVJffcvxoiEqYs2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 10.04.2015 um 11:56 hat Stefan Hajnoczi geschrieben: > On Thu, Apr 09, 2015 at 02:40:00PM +0200, Alberto Garcia wrote: > > On Thu, Apr 09, 2015 at 11:39:28AM +0100, Stefan Hajnoczi wrote: > >=20 > > > > The goal would be to convert this: > > > >=20 > > > > [A] -> [B] -> [C] -> [D] > > > >=20 > > > > into this: > > > >=20 > > > > [A] -> [B] -> [X] -> [D] > > > >=20 > > > > where [D] is the active image and [X] would be a copy of [C]. The > > > > latter would be unlinked from the chain. > > > >=20 > > > > A use case would be to move disk images across different storage > > > > backends. > > >=20 > > > The simple solution to that problem is: > > >=20 > > > Assumption: backing files are read only. (True in most cases.) > > >=20 > > > 1. Copy the backing files using cp(1) or another method. > > > 2. Issue QMP 'change-backing-file' command so that [D] uses [X] inste= ad > > > of [C]. > > >=20 > > > So it can be done today already. > >=20 > > So do you think it would be better to implement this somewhere else? > > The code that I have for QEMU is quite simple, the actual algorithm > > doesn't change, it only needs to do the changing of backing files in > > mirror_exit(). >=20 > I'll take a look at your patch series, maybe there are advantages to > doing it within QEMU. If the patches are simple, I think consistency and avoiding arbitrary restrictions are good enough reasons for having the support in qemu. Eventually we want all nodes to be equal anyway. Kevin --UlVJffcvxoiEqYs2 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJVJ8n8AAoJEH8JsnLIjy/Wk4kP/00bCAqiPSPaGP+C5fvqFmR7 U09s+ute3HaQCksahGy5E21WcvUtbm10YghTrQtr+pqwUZgois6DUKmIc4N2sCkr Tr+K99WwRrSa+WagNB/a5d3d4R2ud1zqcC5dqmAADGRx8VIzC2iGQmIPihVh19Uc T3XITZnt/Kx7QLM/He27x5+F1RjAPcj8miTUJL64Rbil7rTufV9wVODlrLQF9P1k 1l4l6kEfSdGvOgCEwtfupJaGPZkQblJY0HUaDhljqB74uMeVrfSKNJFUCQesIFI1 YhaLX8dyMNaBm/2T9ev+n6bVeAc8evKJpT1mrkGJ48ElJ2LQQdbW4s3zDtQFim+s wkGAyKhcezvdmoueNvkCdoa43TVv0krZ7KW5HUqZUaT9KAjfKqoYCTYO7T3AxuJA BDGlMU6Dr8LQGIEwiDa4D6QIaa8MFcG23sE6qEukgSaGJ+N9KIeW+sEScUUjTSsE Io9goufCr4VJs250iAFBR55YA5on3IjMAEea0BBu1h73HIpXZn0ZjpXUVT6h59Nq MxA6yuTQmfc3eHglJu3RdaFj5H3a7r7V7n5Do0zxcMANFdIKGEy/EtLvutjD4kg7 9YZBWyuXPSACvVcbuuSrEIkTv7yyqlNyvyUlf2g1nM1es6Bd8MdIbdJsPDJovFdi 6U4tghmQurtyIC+ZUKuS =9Tdd -----END PGP SIGNATURE----- --UlVJffcvxoiEqYs2--