openstack team mailing list archive

[Vishvananda Ishaya <vishvananda@xxxxxxxxx>]

Hi Gaurab,

Openstack is not a hypervisor, it is a management layer that sits on top of a hypervisor. Management of the guest filesystem and memory is all done by an underlying hypervisor, Generally KVM or Xen. KVM is essentially kernel module extensions for QEMU (which is a software emulator). I hope this is helpful.

Vish

On Aug 3, 2012, at 3:05 AM, Gaurab Basu <basugaurab88@xxxxxxxxx> wrote:

> Hi Jay,
> 
> Thanks a lot again, trying to get an understanding of the overall process.
> 
> So the file system for qcow2 is sort of managed by qemu(not by openstack itself) ... create etc is done by qemu but read/write from filesystem is also manged by qemu?
> Is the filesystem supported by qemu for all cases(hypervisors other than kvm, or different image formats or when COW layer is not implemented)
> or does openstack have it's own filesystem management as well. 
> 
> And my next question is regarding memory management. In memory blocks are read/write to and from filesystem.
> So this process is supported by openstack ( if so,where should i look in the code for memory management ) or qemu?
> 
> Thanks and Regards,
> Gaurab
> 
> On Thu, Aug 2, 2012 at 10:53 PM, Jay Pipes <jaypipes@xxxxxxxxx> wrote:
> On 08/02/2012 07:47 AM, Gaurab Basu wrote:
> > Hi Jay,
> >
> > Thanks for your reply, it helped me get started.
> >
> > I have been going through the code and some of the sparse docs that are
> > available.
> >
> > This is the code file
> > https://github.com/openstack/nova/blob/master/nova/virt/libvirt/utils.py
> >
> > However I am facing a new issue and require some help. I wanted to
> > modify how openstack handles the cow layer as such and also the qcow2
> > format.
> > It turns out that openstack issues the external command "qemu-img".
> >
> > First of all, is qemu-img internal to openstack ( I mean code for how
> > qemu-img is implemented is in openstack or in qemu )
> > It is in openstack, where is the code located.
> >
> > If it is outside openstack, does that mean i have to change the code in
> > qemu and then link those binaries with openstack.
> 
> QEMU is a totally separate project from Nova, yes. QEMU is written in C
> and has a number of executables such as qemu-img and qemu-nbd, etc. Nova
> calls out to these executables in subprocesses.
> 
> If you want to make changes to QEMU, yes, you would want to look into
> the QEMU contribution process and community.
> 
> Here's where to start:
> 
> http://wiki.qemu.org/Documentation/GettingStartedDevelopers
> 
> Best,
> -jay
> 
> 
> 
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