From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50925) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fLPsf-0005mk-QC for qemu-devel@nongnu.org; Wed, 23 May 2018 05:16:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fLPse-0005km-M8 for qemu-devel@nongnu.org; Wed, 23 May 2018 05:16:25 -0400 Date: Wed, 23 May 2018 11:16:04 +0200 From: Kevin Wolf Message-ID: <20180523091604.GC7523@localhost.localdomain> References: <20180518180440-mutt-send-email-mst@kernel.org> <20180518170956.GI8615@redhat.com> <20180522073555.peibbwoqvbor7nrs@sirius.home.kraxel.org> <20180522171112-mutt-send-email-mst@kernel.org> <20180522150221.GF6233@localhost.localdomain> <20180523021221.GE28114@lemon.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180523021221.GE28114@lemon.usersys.redhat.com> Subject: Re: [Qemu-devel] storing machine data in qcow images? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: "Michael S. Tsirkin" , ehabkost@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, Gerd Hoffmann , stefanha@redhat.com, berrange@redhat.com Am 23.05.2018 um 04:12 hat Fam Zheng geschrieben: > On Tue, 05/22 17:02, Kevin Wolf wrote: > > Am 22.05.2018 um 16:19 hat Michael S. Tsirkin geschrieben: > > > On Tue, May 22, 2018 at 09:35:55AM +0200, Gerd Hoffmann wrote: > > > > Hi, > > > > > > > > > You must /sometimes/ supply the correct machine type. > > > > > > > > > > It is quite dependent on the guest OS you have installed, and even > > > > > just how the guest OS is configured. In general Linux is very > > > > > flexible and can adapt to a wide range of hardware, automatically > > > > > detecting things as needed. It is possible for a sysadmin to build > > > > > a Linux image in a way that would only work with I440FX, but I > > > > > don't think it would be common to see that. > > > > > > > > I think it would be pretty hard to actually build such an image. > > > > > > > > The more critical thing for linux guests is the storage driver which > > > > must be included into the initrd so the image can mount the root > > > > filesystem. And the firmware, bios vs. uefi is more critical than > > > > pc vs. q35. > > > > > > I think we can start by finding a location to embed a string in a qcow > > > image, add ability for qemu-img to set and get this string. We can > > > discuss how it's formatted separately. > > > > If we want it, we'll find a place to store it. > > > > But the first thing we need is a spec for what's actually in it. Just > > storing a machine type hint would be a one-off hack that wouldn't last > > very long before we want to add the next thing. > > > > Essentially, what we need is a description of the virtual machine that > > we suggest to use with this image. We can try to reuse something > > existing there, like libvirt XML or OVF, or invent something new (a JSON > > array describing runtime options?). One difference to existing formats > > is probably that we want only frontends and no backends in the > > description. > > > > Do we really need a uniform way and require compliance to the standard we > choose, and implement verification in the block driver, or can we get away with > a description field that accepts any text and leave it to the user to decide > what to put there? In the header we could assign a Content-type field that > defaults to 'text/plain' to the description, that way apps can mark the data as > "application/ovf" if they want, or whatever the upper layer decides. Yes, we can. But I'm not sure if I want. Providing low-level features without telling users how they are supposed to be used usually results in a big surprise for both sides eventually. Kevin