Description of problem:
Xen doesn't work at all - xenstored shows:
FATAL: Failed to initialize dom0 state: No such device
full talloc report on 'null_context' (total 56 bytes in 3 blocks)
    struct domain                  contains     56 bytes in   2 blocks (ref 0)
        /local/domain/0                contains     16 bytes in   1 blocks (ref 0)
Because of this, xend doesn't correctly start.

Version-Release number of selected component (if applicable):
2.6.16-1.2111_FC5xen0

How reproducible:
Always

Steps to Reproduce:
1. Install and update FC5
2. Boot into the Xen0 kernel
3. Start xend
4. Execute "xm list"
  
Actual results:
"xm list" cannot connect to xend.

Expected results:
"xm list" should return the list of Xen domains as usual

Additional info:
An strace of xenstored shows:
open("/proc/xen/xsd_kva", O_RDWR)       = 10
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 10, 0) = -1 ENODEV (No such
device)

Downgrading to the 2.6.16-1.2096_FC5xen0 kernel fixes the problem.