regarding devices in domU - bug or feature ....

[Himanshu Raj <rhim@cc.gatech.edu>]

Hi Folks,

I am trying to develop device driver for a device as a module. There is a front
end in domU and a back end in dom0. At the domU creation time, a write in xenstore
corresponding to creation of BE device spurs my driver which creates appropriate
data structures etc for BE, totally regardless to the FE driver.
After domU finishes booting, I load the FE driver which talks to BE driver
and yada yada.

Problem comes when I unload the FE driver. It calls xenbus_unregister_driver,
which ends up calling xenbus_dev_remove. This sets the xenbus state for that 
device to XenbusStateClosed. My back end driver then thinks that FE device has
gone away and removes the BE device. Needless to say, further loads of FE driver
are useless. If I remove that piece of code (which acts on XenbusStateClosed),
then the BE device hangs around even after the domU has shut down.

IMHO, shouldn't there be a similar job of device *removal* done by xm shutdown
as it is done by xm create? Then proper device removal will only happen when
a guest shuts down, rather when its driver is unloaded. Or there is something
totally wrong with the way I understand this issue.

Best regards,
Himanshu

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Himanshu Raj
PhD Student, GaTech (www.cc.gatech.edu/~rhim)
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