On Fri, Oct 21, 2011 at 10:30:39AM +0200, Kevin Wolf wrote: > Am 20.10.2011 23:48, schrieb Josh Durgin: > > On 10/20/2011 12:24 PM, Daniel P. Berrange wrote: > >> On Thu, Oct 20, 2011 at 11:30:42AM -0700, Josh Durgin wrote: > >>> We're working on libvirt support for block device authentication [1]. To > >>> authenticate, rbd needs a username and a secret. Normally, to > >>> avoid putting the secret on the command line, you can store the secret > >>> in a file and pass the file to qemu, but when this is automated, > >>> there's no good way to know when the file can be removed. There are > >>> a few ways to pass the secret to qemu that avoid this problem: > >> > >> This is the same problem the iSCSI block driver currently faces, > >> and also if the Curl/HTTP block driver wanted todo authentication > >> we'd hit this. So it isn't unique to Ceph/RBD. > >> > >>> 1) pass an fd to an unlinked file containing the secret > >>> > >>> This is the simplest method, but it sounds like qemu developers don't > >>> like fd passing from libvirt. [2] > >> > >> That would be workable, but it means people trying to run the libvirt > >> QEMU command line themselves, would have to remove some args. > > > > Isn't this already the case for chardevs? I can understand not wanting > > more things like that though. > > > >>> 2) start guests paused, without disks requiring authentication, then > >>> use the drive_add monitor command to attach them > >>> > >>> This would make disks with authentication somewhat of a special case > >>> in libvirt, but would be simple to implement, and require no qemu changes. > >> > >> This makes it very hard for people to take the libvirt QEMU command line > >> and run themselves, since now an entire chunk of it is just missing. > >> So I really don't want to go down this route. > >> > >>> 3) start guests paused, then send the secret via a new QMP/HMP > >>> command (block_set_conf<key> <value>?) > >>> > >>> This is a larger change, but it would be more generally useful for > >>> changing configuration at runtime. > >> > >> I don't think you need to try to solve the problem of a general > >> purpose 'set configuration' command here, not least because that > >> will likely get you drawn into a huge discussion about qemu device > >> configuration in general which will likely never end. > >> > >> We already have a 'block_passwd' command for setting qcow2 decryption > >> keys. These aren't decryption passwords, rather they are authentication > >> passwords, so they're a little different, but I think this command could > >> still likely be leveraged for Ceph/iSCSI/etc auth passwords. > >> > >> Ideally, we want to cope with having both a decryption& auth password > >> for the same block device. eg, an encrypted qcow2 image accessed, over > >> HTTP would require both. In these case there are 2 block drivers involved, > >> the 'qcow2' driver and the 'http' driver. So perhaps an extra parameter > >> for the 'block_password' command to identify which driver the password > >> is intended for is the right approach. If omitted,we'd default to 'qcow2' > >> for back compat. > >> > >> So eg, for a encrypted qcow2 disk accessed over http > >> > >> -drive file=http://fred@host/my.iso,format=qcow2,id=mydrive > >> > >> the app would invoke > >> > >> { "execute": "block_password", "argument": { "device": "mydrive", > >> "driver", "qcow2", > >> "password", "12345" } } > >> { "execute": "block_password", "argument": { "device": "mydrive", > >> "driver", "curl", > >> "password", "7890" } } > >> > >> For Ceph/RBD with a plain file, you'd just do > >> > >> > >> { "execute": "block_password", "argument": { "device": "mydrive", > >> "driver", "rbd", > >> "password", "7890" } } > >> > > > > This sounds good to me, although the same driver might use > > authentication and encryption. Adding another argument to specify 'auth' > > or 'encryption' would fix this, i.e.: > > > > { "execute": "block_password", "argument": { "device": "mydrive", > > "driver": "qcow2", > > "use": "encryption" > > "password": "12345" } } > > > > I'll prepare a patch if there are no objections to this approach. > > This proposed interface solves a problem that is currently purely > theoretical. With blockdev-add and friends, we'll get all of this for > free, so I'm not excited about adding something preliminary now even > though there's no practical need.
Ok. > For the rbd driver, please use the existing interface that qcow2 uses > for encrypted images. If you're ok with just reusing 'block_passwd' as it is today, with no arg parameters, then that's fine with me too. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
