Help/problems with blktap on xen-unstable

[Roland Paterson-Jones <roland@rolandpj.com>]

Hi

I've been trying to play with the new blktap support in xen-unstable.

First, an observation - blktapctrl is pinned at 100% CPU:
----------------------------------------------------------------------------------------------------------------- 

top - 17:29:48 up 4 days,  2:02,  3 users,  load average: 0.90, 1.01, 1.00
Tasks:  83 total,   3 running,  80 sleeping,   0 stopped,   0 zombie
Cpu(s): 15.2% us, 34.9% sy,  0.0% ni, 49.9% id,  0.0% wa,  0.0% hi,  
0.0% si
Mem:    262356k total,   240936k used,    21420k free,     4832k buffers
Swap:   917496k total,    96976k used,   820520k free,    67180k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
3807 root      25   0 11040  508  400 R 99.9  0.2   0:17.56 blktapctrl
   1 root      16   0  1744  124   92 S  0.0  0.0   0:00.87 init
------------------------------------------------------------------------------------------------------------------ 


Then, I am trying to follow the README to get an image file mounted via 
tap:aio in dom0 (as a precursor, or course, to using it for rootfs in a 
domU).

So:

[root@dom0-0-50-45-5d-59-aa tmp]# xm block-attach 0 
tap:aio:/tmp/sparse.img /dev/xvda1 w 0
...
[root@dom0-0-50-45-5d-59-aa tmp]# xm block-list 0
Vdev  BE handle state evt-ch ring-ref BE-path
51713    0    0     3      15     8     /local/domain/0/backend/tap/0/51713

But
[root@dom0-0-50-45-5d-59-aa tmp]# mount /dev/xvda1 /mnt/tapaio
mount: you must specify the filesystem type
[root@dom0-0-50-45-5d-59-aa tmp]# mount -t ext3 /dev/xvda1 /mnt/tapaio
mount: special device /dev/xvda1 does not exist

And, indeed, there's no /dev/xvda1.

Help!
Roland