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[Xen-devel] bug: Cannot create vbd / cannot create vif

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] bug: Cannot create vbd / cannot create vif
From: Eric Windisch <lists@xxxxxxxxxx>
Date: Fri, 09 Jun 2006 11:06:12 -0400
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Last week, I mentioned an error to xen-users an error I was receiving, relevant description provided below. I've seen several mailing list posts describing a similar problem as far back as December, 2005. This seems to be a problem plaguing all Xen 3 releases (to date).

The error I receive is (approximately) '(vif) could not be connected'. If I comment the 'vif=' line in the domain's configuration, I then receive '(vbd) could not be connected'. Both messages were also followed by "Hotplug scripts not working." (I am using udev)

Upon review, I'm pretty certain the problem is happening when a new domain is created that is specifying a MAC address identical to that assigned to an existing guest domain. When a new domain comes online with the conflicting MAC address, Xen will rightfully refuse to create the vif, and exits -- but it does NOT properly clean up. After that point, Xen will refuse to create ANY new guest domains, even if properly-configured. The only way I am aware of to then create a new domain is to reboot the iron. I haven't yet found a workaround.

Once the system has encountered this problem, I see several variables within xenstore-ls associated with each of the domains which failed to 'create'. I manually removed the associated variable trees with xenstore-rm, but I still wasn't able to create a new domain, again with the message "(vdb) could not be connected". Killing xenstored and restarting xend did not help, nor did nuking xenstored's tdb file.

While we know it is already dangerous to allow incoming live migrations from untrusted networks, imagine if someone was to cause the above-described bug via a live migration?

Please let me know if you need further information to reproduce the error. My host system is a PentiumD 830 /w 4gb memory -- that is a dual-core x86_64 processor.

Below is an excerpt from xenstore-ls showing information about a domain (rjackson) which was never created.. (I attempted to start it a few times, as you can see)

Thank you.

--
Eric Windisch


local = ""
domain = ""
 0 = ""
  cpu = ""
   0 = ""
    availability = "online"
   1 = ""
    availability = "online"
  memory = ""
   target = "1896448"
  name = "Domain-0"
  console = ""
   limit = "1048576"
  vm = "/vm/00000000-0000-0000-0000-000000000000"
  domid = "0"
  backend = ""
   vbd = ""
    23 = ""
     2049 = ""
      domain = "rjackson"
      frontend = "/local/domain/23/device/vbd/2049"
      dev = "sda1"
      state = "5"
      params = "mapper/XenDomains-rjackson"
      mode = "w"
      frontend-id = "23"
      type = "phy"
     2050 = ""
      domain = "rjackson"
      frontend = "/local/domain/23/device/vbd/2050"
      dev = "sda2"
      state = "1"
      params = "mapper/Swap-rjackson"
      mode = "w"
      frontend-id = "23"
      type = "phy"
    24 = ""
     2049 = ""
      domain = "rjackson"
      frontend = "/local/domain/24/device/vbd/2049"
      dev = "sda1"
      state = "5"
      params = "mapper/XenDomains-rjackson"
      mode = "w"
      frontend-id = "24"
      type = "phy"
     2050 = ""
      domain = "rjackson"
      frontend = "/local/domain/24/device/vbd/2050"
      dev = "sda2"
      state = "1"
      params = "mapper/Swap-rjackson"
      mode = "w"
      frontend-id = "24"
      type = "phy"
    25 = ""
     2049 = ""
      domain = "rjackson"
      frontend = "/local/domain/25/device/vbd/2049"
      dev = "sda1"
      state = "5"
      params = "mapper/XenDomains-rjackson"
      mode = "w"
      frontend-id = "25"
      type = "phy"
     2050 = ""
      domain = "rjackson"
      frontend = "/local/domain/25/device/vbd/2050"
      dev = "sda2"
      state = "1"
      params = "mapper/Swap-rjackson"
      mode = "w"
      frontend-id = "25"
      type = "phy"

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