RE: [uml-devel] RE: [uml-user] are 'persistent', 'undoable', and 'non-persistent' filesystems possible

[Caleb C. <jo...@cr...>]

> -----Original Message-----
> From: Joe Thornber [mailto:tho...@bt...]
> Sent: Tuesday, May 01, 2001 10:04 AM
> To: Caleb Crome
> Subject: Re: [uml-devel] RE: [uml-user] are 'persistent', 'undoable',
> and 'non-persistent' filesystems possible
>
>
> On Tue, May 01, 2001 at 09:56:42AM -0700, Caleb Crome wrote:
> > - Joe Thornber wrote
> > > I've been using UML for LVM development since Christmas, it's saved me
> > > a *lot* of time.  If you do want to use LVM with uml you'll have to
> > > make sure that the files used by the ubd driver are open before LVM
> > > tries to use them; I have a hacky patch which just opens all
> the device
> > > files on boot.
> > >
> > > I presume you are referring to LVM's snapshot facility with regards to
> > > 'undoable partitions'?  At the moment snapshot's are read only,
> > > however it shouldn't take longer than a couple of hours to get
> > > writeable snapshots running.  Have a dig in the code.
> >
> > No, I wasn't actually referring to LVM's snapshot facility.  It just
> > occurred to me that LVM is a nice place to catch block
> read/write requests
> > from user space and map them around properly to implement
> whatever kind of
> > persistency scheme is needed.  I suppose I could simply build a
> new block
> > device which uses a another block device and a file to track changes.
>
> It seems to me that writeable snapshots are what you really want.

Fascinating.  I have not experience with LVM.  That sounds very cool.  How
to you enable LVM within UML.  It's not there when I do make menuconfig.
Also, can you point me a bit in the right direction to where I might work on
writable LVM snapshots?

I guess this is getting quite off topic, since this is really unrelated to
UML -- except for the fact that UML makes debugging about a zillion times
easier (Thanks Jeff).

Writable snapshots seem like they would be of interest to much of the linux
community -- not just UML folks.



>
> > The most important thing I'm looking for in this system
> (besides it working)
> > is the ability to have a single read only root file system
> which can boot
> > many UMLs.
>
> Yep, root image on an LV, boot off a writeable snapshot of this LV.
> Each vm has different snapshot storage.

Cool.

>
> I don't think this discussion is on the list anymore, I pressed the
> wrong reply button.  Feel free to forward it to the list.

Right.  I've put it back on the list, at least for this posting.  Maybe it's
appropriate to take this off the list and we can post again if we get
something working.

-Caleb