Re: Disk naming (Was Re: [Xen-devel] [PATCH] Guest boot loadersupport [1/2])

[Adam Heath <doogie@xxxxxxxxxxxxx>]

On Fri, 15 Apr 2005, Mark Williamson wrote:

> > > Does that answer your question or am I still off target?
> >
> > It does.  So, it's the blkback in dom0 that requires a device node.
>
> Yup, that's why we have to go through the gyrations with the block scripts in
> order to make things look nice at the user level.
>
> > How
> > about it the blkback were extended to support files in filesystems?
>
> Right now, all the backend needs to know about is what block device to plumb
> requests through to.  I don't really think there's a nice way to make it
> aware of files within filesystems without effectively reimplementing the
> loopback driver.

The blkfront driver should request id+offset+length from the blkback driver.
The blkback driver then converts the id into either a device, or a file.
Seems rather straight forward to me.

> From what I've heard the loop driver itself could use a bit of work to make it
> really useful: it comes at a performance / memory usage hit :-(.  We
> recommend using LVM for any really serious environments for this reason.
>
> An alternative architecture would be to have a userspace daemon for file
> backed VBDs, using the blktap framework (unstable tree only).  I'm not sure
> if this would work any better than the current way of doing files, tho...

blktap?  Is that similiar to what I described above?

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