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

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> 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?

Cheers,
Mark

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