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[Xen-devel] Bugs with block devices to domU - let's find solution


I have the same bug, that've been disscussed before - domU can't find any block devices and crashes with "Unable to mount root fs". I've spend a week under heavy debugging and find, that this bug take place because dom0 backend driver can't read parameter physical-device from xenstore. For example /local/domain/0/backend/vbd/1/776/physical_device, where 1- domU id, 776=0x308 - major and minor numbers of block device, which will used by domU. This parameter must be written by script /etc/xen/scripts/block, which must start like /etc/xen/scripts/vif-bridge any time as domU starts, but it doesn't.

So, there is a question to xen developers: when and how must this script must been started ?

To start domU i comment out block in backend driver, where this parameter must be obtained and give explicitly value for that variable:

file -    linux-.../drivers/xen/blkback/xenbus.c
function - backend_changed

   err = xenbus_scanf(NULL, dev->nodename,
              "physical-device", "%li", &pdev);

with, for example:
pdev=0x307;   //hda7 - physical device

Guryanov Dmitry

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