Re: [Libguestfs] Fwd: Re: VirtFS Query
On Thu, 29 Sep 2011 17:12:22 +0100, "Richard W.M. Jones"
<rjones(a)redhat.com> wrote:
On Thu, Sep 29, 2011 at 09:19:03PM +0530, Harsh Bora wrote:
> Richard, FYI.
>
> On Wed, 28 Sep 2011 17:05:42 +0530, Harsh Bora
> <harsh(a)linux.vnet.ibm.com> wrote:
> >Hi Aneesh,
> >
> >Richard asked me if we have any plans to provide a solution for this use
> >case:
> >
> >https://www.redhat.com/archives/libguestfs/2011-September/msg00089.html
> >
> >IIUC, VirtFS as a rootfs is targeted towards this requirement only,
> >right? Any inputs ?
> >
>
> The right way to do this is to use a export path /guest and bind mount
> needed directories within. VirtFS just export /guest and everything
> works out easily. I already have autotest driving virtFS as root. So
> that works easily
That's not going to work for us.
Firstly bind mounting requires root, which is no good for libguestfs.
Another alternative suggested by pekka for tools/kvm (native linux kvm)
is to create a directory layout as below
in /guest1-export/
bin -> /host/bin
sbin -> /host/sbin
usr -> /host/usr
lib -> /host/lib
etc
proc
var
host
and qemu starts with two export path /guest1-export as root and / of the
common image (or host) as /host on guest. Now 9p resolves symbolic links
in the guest. So which ever directory that need to be shared with host
can have a symlink and everything works
Secondly there are no directories that we could bind mount. We
really
need the flexibility outlined in that email. Just two examples of
this (there are more):
- /usr/sbin in the appliance is not the same as /usr/sbin on the
host. The appliance version should contain a subset of the host
directory, plus at least one extra binary (/usr/sbin/guestfsd).
- Because /etc files on the host can be arbitrarily modified, we need
to construct our own /etc directory, with files from the host and
files that we supply.
What's may help here is some sort of plugin or passthrough mechanism
letting us add our own 9p server/plugin without pushing all the
complexity we need into qemu sources.
More here:
http://libguestfs.org/febootstrap.8.html#supermin_appliances
There is some level of plugability with VirtFS server already. You can
look at virtio-9p-local.c, virtio-9p-handle.c and virtio-9p-synth.c in
the example. git://repo.or.cz/qemu/v9fs.git
-aneesh