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Re: installing a 4.1 DOMU
On Wed, 18 Jul 2012 12:36:24 +0100
Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost> wrote:
> That depends on how you declared your partitions and exposed them to
> If the domU tries to overwrite the sector containing the labels then
> the dom0 backend will likely return EROFS, hence "read only
> file-system." See  for an example.
Sorry for not being clear. See below.
> Using phy: declares a device, so anything passed as a device will be
> used as a virtual disk, _even_ if it is a partition/label within dom0.
> Let's illustrate this: suppose you create a disk.img file, then label
> it through vnd(4). What you do is:
> - vnconfig -c vnd0 disk.img # declares disk as a vnd(4) device
> - disklabel vnd0 # create labels in disk.img
> Now you have labels on the vnd0 device, vnd0 is the whole disk (but
> not necessarily vnd0a as the label does not necessarily covers the
> whole disk).
In my case both the a: and d: partitions covered the whole disk (=
disk.img in your example). Of course, they differ in filesystem type
(4.2BSD versus unused). Reading the thread you quoted , it seems
that the primary issue is how the kernel handles a region of the disk
that includes the disk label. Partition a: includes the read-only
disklabel sector and enforces read-only semantics, whereas partition d:
does not enforce the same semantics. Thus, I should have been using
> If you pass phy:/dev/vnd0a, you are saying: "label/partition a will
> act as a virtual disk with regard to domU." It will be treated as a
> disk within domU, and used as one.
Yes, that is what I intended. From above I guess what I really wanted
was to pass phy:/dev/vnd0d. When I do this, the disklabel can be
written within sysinst in DOMU just fine.
So, in the end, I have the following:
disk = [ 'phy:/dev/vnd0d,xvda,w' ]
root = "xbd0a"
> That's why it is preferable to use file:/path/disk.img for image
> files, because you expose the entire file as a disk to the domU, so
> they are treated the same way whether you use them within domU
> (through xbd(4)), or within dom0 (through vnd(4)).
I'm not sure I know what 'that' refers to, but now I think I understand
it much better.
Yes, it would be more direct to use file:, but that seems not to be
supported with xl. I suppose that will come in time.
> Hope that it is now a bit clearer :)
Yes, much clearer. Thanks for your help and for your work on this.
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