Re: [libvirt] [sandbox PATCH 2/3] Add configuration object for disk support

On Wed, Jun 17, 2015 at 09:43:23AM +0200, Cedric Bosdonnat wrote: > Hi Daniel, > > On Thu, 2015-06-11 at 14:47 +0100, Daniel P. Berrange wrote: > > On Wed, Jun 10, 2015 at 01:40:09PM +0200, Eren Yagdiran wrote: > > > Add the config gobject, functions to store and load the new configuration > > > fragments and test. This will allow creating sandboxes with attached > > > disk with a parameter formatted like file:hda=/source/file.qcow2,format=qcow2 > > > > > +/** > > > + * gvir_sandbox_config_add_disk_strv: > > > + * @config: (transfer none): the sandbox config > > > + * @disks: (transfer none)(array zero-terminated=1): the list of disks > > > + * > > > + * Parses @disks whose elements are in the format TYPE:TARGET=SOURCE,FORMAT=FORMAT > > > + * creating #GVirSandboxConfigMount instances for each element. For > > > + * example > > > + * > > > + * - file:hda=/var/lib/sandbox/demo/tmp.qcow2,format=qcow2 > > > + */ > > > > One of the goal of the libvirt sandbox code is to insulate apps from > > needing to know hypervisor specific differences. The guest side disk > > device name is one such big difference. Many hypervisors, including > > kvm, will not even honour requested names - you just get whatever > > name the guest decides to give you. Essentially the only thing that > > libvirt guarantees is the disk ordering. ie if you configure two > > disks one with hda and one hdb, libvirt will ensure hda appears > > before hdb on the bus or controller. > > > > So I don't think we should include the target device name in our > > configuration syntax here. We should just document that disks > > will be added to the guest in the same order that you supply > > them to virt-sandbox command line in. The actual device names > > will vary according to the hypevisor and guest os. > > Right. But I think we then need to ask for the bus type then, so that we > know whether we'll have ide, scsi or whatever. Then we could have the > option like: > > file:ide=/path/to/source,format=fmt > > And of course document that the disks will be added in the same order. > > Does it sound better for you? Not really - that is still not achieving our goal that users should not need to details about the hypervisor used when configuring a sandbox. The goal is that the CLI args to virt-sandbox should be unchanged, no matter what libvirt URI is provided. Now of course in the case of virtualized disks, what appears inside the sandbox could be differently named - ideally we'd find a way to insulate users from that aspect too. In normal Linux there are various symlinks /dev/disk/by-{uuid,id,path} available which link back to /dev/[sda,vda,hda,etc]. These are created by udev, but we're not running that. I wonder if we could make use of that concept though - create /dev/disk/by-tag directory and then in the cli args we could allow a simple tag. eg file:foobar=/path/to/source,format=fmt and then populate a symlink /dev/disk/by-tag/foobar -> /dev/sda