[Libguestfs] Can't access remote URI

Wanlong Gao gaowanlong at cn.fujitsu.com
Thu Dec 20 10:30:12 UTC 2012

On 12/20/2012 05:53 PM, Richard W.M. Jones wrote:
> On Thu, Dec 20, 2012 at 05:30:03PM +0800, Wanlong Gao wrote:
>> On 12/20/2012 05:08 PM, Richard W.M. Jones wrote:
>>> On Thu, Dec 20, 2012 at 04:00:10PM +0800, Wanlong Gao wrote:
>>>> Hi Rich,
>>>> We just found that the libguestfs can't access the remote URI.
>>>> When doing guestfs__add_drive_opts(), we always add files from
>>>> local system, it's related the -c|--connect option.
>>>> As I know, we are using local kernel to lunch the min-guest,
>>>> and it's hard to attach remote disks to our local min-guest.
>>>> Our test team found this problem by using following command,
>>>> # virt-sysprep -c qemu+ssh://<host>/system -d domname
>>>> Then, for example the path of remote disk is /work/rhel.img,
>>>> but we are about to access the /work/rhel.img locally.
>>>> So, IMHO, if we are about to not support the remote URI, we
>>>> should give a error message first. But access local disks
>>>> instead of remote disks are definitely wrong here.
>>>> Maybe we also need document this.
>>>> Any thoughts?
>>> John Eckersberg is working on implementing this for libguestfs 1.22.
>>> Most of the libvirt support has been done already, but there is some
>>> more libvirt and libguestfs work.
>>> As for reporting an error, it's difficult because libvirt doesn't give
>>> a simple way to find out if a URI is "remote" or not (whatever
>>> "remote" means).  And even if libvirt did, it's not necessarily true
>>> that remote URIs wouldn't work, eg. if the user attached a LUN to both
>>> the remote and local machine.
>> So, at this time, we should report a useful message to user but not just
>> fail without any thing. Right?
> I don't know how you can report a useful message, since it's not
> obvious if a libvirt URI is remote.  eg. How about the URI
> "qemu+ssh://foo/session" where the hostname of the local machine is
> "foo.example.com"?  Or the hostname is "bar.example.com" but the local
> DNS contains a PTR record "foo" -> "bar"?

Oops, I don't have a good idea either.
So, as John is doing this work, can you share the working progress and the roadmap
so that we can help doing something?

Wanlong Gao

> Rich.

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