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

[Eric Windisch <lists@xxxxxxxxxx>]

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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