[Xen-users] xen 4.0.0, blktap2 new device limit problem

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

So after noticing that iostat shows a new device (tapdevi, tapdevj,
etc.) every time a domU is (re)started, I decided to run this test
script

#######
for n in `seq 1 257`;do tapdisk2 -n aio:/z/template/hda.img;echo 1 >
/sys/class/blktap2/blktap*/remove;done
#######

... which, accoring to
http://lxr.xensource.com/lxr/source/tools/blktap2/README, should
assign the disk in dom0, and immediately remove it afterwards. No domU
is currently running at that time. In the end of the output I see

#######
/dev/xen/blktap-2/tapdev254
/dev/xen/blktap-2/tapdev255
failed to allocate new device: 12
-bash: /sys/class/blktap2/blktap*/remove: No such file or directory
#######

at that time, /dev/xen/blktap-2 has lots of device char/block devices,
ending with blktap255 and tapdev255. Removing those files doesn't
help.

At this point, attaching the device as blktap doesn't help. With
blktap module loaded but xenblktap module not loaded:

#######
# xm block-attach 0 tap:aio:/z/template/hda.img xvda w
Error: Failed to create device.
    stdout: failed to allocate new device: 12
    stderr:
Check that target "/z/template/hda.img" exists and that blktap2 driver
installed in dom0.
Usage: xm block-attach <Domain> <BackDev> <FrontDev> <Mode> [BackDomain]

Create a new virtual block device.
#######

with the old xenblktap module loaded:
#######
# xm block-attach 0 tap:aio:/z/template/hda.img xvda w
Error: The file "/z/template/hda.img" is already used
Usage: xm block-attach <Domain> <BackDev> <FrontDev> <Mode> [BackDomain]

Create a new virtual block device.
#######

Any ideas on how to get xen to reuse those tap devices?

-- 
Fajar

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