From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48312) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fxZLy-0007l5-CR for qemu-devel@nongnu.org; Wed, 05 Sep 2018 11:04:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fxZLv-0001Ib-KL for qemu-devel@nongnu.org; Wed, 05 Sep 2018 11:04:21 -0400 Date: Wed, 5 Sep 2018 17:04:08 +0200 From: Kevin Wolf Message-ID: <20180905150408.GD4489@localhost.localdomain> References: <20180828142626.GM122225@angien.pipo.sk> <20180903150311.GC14463@dhcp-200-186.str.redhat.com> <20180904141730.GC3803@andariel.pipo.sk> <20180904150042.GE3803@andariel.pipo.sk> <20180904153436.GC4371@localhost.localdomain> <20180905123813.GF3803@andariel.pipo.sk> <20180905140238.GG3803@andariel.pipo.sk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="mvpLiMfbWzRoNl4x" Content-Disposition: inline In-Reply-To: <20180905140238.GG3803@andariel.pipo.sk> Subject: Re: [Qemu-devel] [PATCH 1/2] commit: Add top-node/base-node options List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Krempa Cc: Eric Blake , Alberto Garcia , qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com --mvpLiMfbWzRoNl4x Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 05.09.2018 um 16:02 hat Peter Krempa geschrieben: > On Wed, Sep 05, 2018 at 08:48:15 -0500, Eric Blake wrote: > > On 09/05/2018 07:38 AM, Peter Krempa wrote: > >=20 > > > block-commit is able to reopen the format layers and works as expecte= d. > > >=20 > > > Unfortunately though the 'read-only' option is actually useful as the > > > curl-driver does not work without it: > > >=20 > > > -blockdev {"driver":"http","url":"http://ftp.sjtu.edu.cn:80/ubuntu-cd= /12.04/ubuntu-12.04.5-alternate-amd64.iso","node-name":"libvirt-2-storage",= "discard":"unmap"}: curl block device does not support writes > > >=20 > > > We obviously can encode that knowledge into libvirt but it will be ha= rd > > > to undo if qemu eventually supports writes in the curl driver. > > >=20 > > > Which other protocol drivers don't support writes? in case we have to= go > > > this way. > >=20 > > When an NBD server exported an image as read-only, the NBD block client > > cannot request write permissions. But that's a runtime discovery proce= ss, > > not a limitation of the block driver itself. >=20 > Hmmm, that's unfortunate. Because in some cases we don't know this fact > upfront in libvirt and we also don't know whether an user might attempt > to block-commit at some time. >=20 > We probably do need a way to specify that we want > 'read-write-if-possible' behaviour. So after all, maybe we should try whether a read-only=3Dauto is possible, which would reopen the image file on demand (depending on whether some user of the node requested BLK_PERM_WRITE etc.) Kevin --mvpLiMfbWzRoNl4x Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJbj/BoAAoJEH8JsnLIjy/WBaIP/jfC3+gxWSHpPb6lS9kv5yqg n2lV9hYsNU6k5gNV46N1jdgvPcKYAUdWuq2HNsqkhBLQFXrvQ3Y1IUekvR+dN2Iv BrtHMZLpWr0TUU9xr0n/A1M069MnPvbWVX9CzCHuTu4IwWeZQCKKDbU+UgpKyqdr TDdycwIRaqAsnrilvQO89KW2jx3kv4iNmohh0crY7DGW9VpkNAFeW49W5Ylr76Um UD+VZZq2S6bKUB5g6rAYbWxvEWzjmA7skJDxlOMXXGdBg2i6N68BPURfEqLfCGD8 bScWg2lfTEdPC4fLN7iPW5bT4q8lgac+oMFik1QpWPxmR2X8pYFU5w/kOGTkgGa4 pMzPJV4aGKnOI9eN6OoHYzh5hIvNqp/K8yeq2/uTrFAZP/z/WeQYFfY9cxojCTNp EH8jfvrA6H5L17DS3lXQ1WosPIubdSeQsrdfKUwMwLy2LiJ/pCVs3d2b1m9t+1fZ xJSHr4OuAVz6BGwstvMNe3n7addC/S6cSYer10gaa/bChs59Tvi9/gZtusf5lA31 UQ+JlBa62BEopCvx6cruKtEUcHo2hR8A/+RPpvZV6YjuxORXAmF9FU+kqz3ILobf a4WvHAC4bI8IkwnLH30p1AHpEdTbFoA6RvI/mFm5PLMa2RyIRTvbmu0PYJviKpwR JHUrpQRtRzhOsMuRxW/m =jNmx -----END PGP SIGNATURE----- --mvpLiMfbWzRoNl4x--