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Re: [Xen-API] look into VHD VDI from Control Domain in XCP 1.6

  • To: xen-api@xxxxxxxxxxxxx
  • From: George Shuklin <george.shuklin@xxxxxxxxx>
  • Date: Tue, 08 Jan 2013 22:07:40 +0400
  • Delivery-date: Tue, 08 Jan 2013 18:07:54 +0000
  • List-id: User and development list for XCP and XAPI <xen-api.lists.xen.org>

Ok, here important stuff. When VBD is plugged to dom0, it plugging not as 'normal' device (with udev attention), but as device in /dev/sm/backend.

Here sample log (change uuids on you taste):

xe vbd-create vm-uuid=53c3d878-b60b-48ec-aaac-73f7adf9ab3d vdi-uuid=5e2c31a5-1d1b-4abe-9892-1fa3bc47b532 device=6
xe vbd-plug uuid=407eb3a6-919f-f605-0883-e12aaa91321d

ls -la /dev/sm/backend/55ea20d2-8611-1121-9e9e-c26b35ac1852/
drwxr-xr-x 2 root root     80 ÐÐÐ  8 21:57 .
drwxr-xr-x 3 root root     60 ÐÐÐ 18 17:40 ..
brw------- 1 root root 253, 0 ÐÐÐ 8 21:57 5e2c31a5-1d1b-4abe-9892-1fa3bc47b532 -rw-r--r-- 1 root root 852 ÐÐÐ 8 21:57 5e2c31a5-1d1b-4abe-9892-1fa3bc47b532.attach_info

I have no idea why '55' uuid (and what it means), but 5e2c31a5-1d1b-4abe-9892-1fa3bc47b532 is block device after whole VHD tree joining/parsing and so on.

You can see actual path in xe vbd-list output (device field).

05.01.2013 11:33, Alexandre Kouznetsov ÐÐÑÐÑ:

El 04/01/13 23:14, George Shuklin escribiÃ:
Use xe vbd-create between vdi and dom0 (which is normal VM mostly), and
xe vbd-plug.
Yes, that's what I have done following the example from Citrix forum.

In case of a normal DomU:
I create VBD linking the VM with VDI,
I issue vbd-plug,
the block device becomes visible in dmesg under DomU.

In case of Dom0:
I create VBD linking the VM (vm-list refers to it as "Control Domain", no mistake) with VDI,
I issue vbd-plug,
no sign of the new block device in dmesg or under /dev.

You can see some sample usage in 'xe-edit-bootloader' command (somewhere
in /opt/xensource/)
Hm. I believe I'm doing it just the same way as in the script, except by the "device=" directive for vbd-create, use specific string like "xvdn". Should it make the difference? Can't test, I shot down my testing range before leaving the office.

So, must I understand that the XCP's regular way of manipulating VDI's contents from within Dom0, is attaching the VDI to it via a VBD? Looks like a good abstraction, except that it won't work that easily on a host without XCP infrastructure (for example, in some rescue scenario).

Then, what vhdpartx is good for?


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