5 messages in com.xensource.lists.xen-develRe: [Xen-devel] About block device ma...
FromSent OnAttachments
Nuutti Kotivuori22 Dec 2004 05:52 
Mark Williamson22 Dec 2004 06:18 
Nuutti Kotivuori22 Dec 2004 06:57 
M.A. Williamson24 Dec 2004 06:08 
Nuutti Kotivuori28 Dec 2004 14:31 
Subject:Re: [Xen-devel] About block device mapping for guests
From:Nuutti Kotivuori (nak@iki.fi)
Date:12/22/2004 06:57:44 AM
List:com.xensource.lists.xen-devel

Mark Williamson wrote:

Yes you can choose an arbitrary IDE or SCSI drive's major / minor pair and export as that. There's no difference to the backend driver, the frontend in the guest uses different blocksize for fake IDE vs fake SCSI, I think.

Right. Uh. I'll take a peek at the code to get the exact answer.

It's technically possible to make the frontend behave more like a CD drive, it's just that there's not a lot of demand for this, so it's not implemented.

Right, understood. Seems like this need would be better served by being able to give entire IDE/SCSI devices to some guests, so they can run all the IDE/SCSI commands they will ever need.

Guest domains can't use devfs because the frontend driver doesn't support it. The developers feeling is that since devfs is deprecated, it's probably not worth the pain of adding support for.

I assume this specifically means that guest domains will not have the block devices created by devfs at all - but if one were to manually create the block devices with the correct major and minor, it would work.

I can understand that it might not be worth the effort - but larger warnings somewhere that 'devfs will not work, plain dev or udev will work' might be in order.

Yes, all Xen virtual devices should appear in SysFS in the guest, which udev will use to do the right thing - this should all work fine.

Hmm. How will the devices be named under sysfs? If I just specify a major and minor device number, where does Xen dig up the name it should be registered under? And how does udev pick the right name for the actual device file?

In the guest, sysfs will show block devices with whatever major / minor was specified. It won't tell you what the drive is mapped to in dom0.

State regarding which block devices in dom0 are mapped to what in the guests is maintained inside Xend.

Right.

HTH,

Immensely. Now I know why none of my domains ever manage to find a root device ;-)

-- Naked

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