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:

> > But what does xend read(or pass to the kernel) to enable the domU to access
> > the data?  If xend(or the kernel) doesn't care, wouldn't it be more
> > efficient to pass the raw file(or device, in the case of iscsi/etc)?
>
> I think we're still talking cross purposes here.  Also, when I wrote the
> previous e-mail I wasn't remembering everything about the code ;-)
>
> Xend enables domU to access the data by telling the blkback driver in dom0's
> kernel to export a given dom0 block device to the guest.  It has to be a
> block device.  The purpose of the block script is a) to make sure such a
> block device exists (by binding something to it if necessary) and b) to tell
> Xend what it is.
>
> For file backed VBDs, the script has to find a free loop device and bind the
> file to it so that there is a block device for the backend to export in the
> first place.  For the SAN / iSCSI setups discussed the script may just serve
> the purpose of finding the correct block device.
>
> In either case, it has to echo the device node to Xend so that it knows what
> the blkback should be told to export.  For things like NBD and loop files,
> this device node is also used to unbind the device after the domain is
> destroyed.
>
> 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.  How about
it the blkback were extended to support files in filesystems?

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