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RE: [Xen-devel] bug in usbback

To: "Noboru Iwamatsu" <n_iwamatsu@xxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] bug in usbback
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Mon, 27 Jul 2009 11:23:06 +1000
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Thread-topic: [Xen-devel] bug in usbback
> You mean:
> - Your version of usbfront NOT respond to Reconfiguring state.
>    It's not bug of original usbfront.

Correct. I was not responding at all to 'Reconfiguring' (I didn't even
know they existed at the time - I was just plugging my generic xenbus
routines into a skeleton usb driver).

> - When usbback is in Reconfiguring state and usbfront NOT respond to
>    that, rebooting domU causes the BUG.

Yes. Actually just stopping DomU is enough to cause the bug. It doesn't
appear to matter if it restarts or not. I was able to work around the
problem by writing 'Reconfiguring' and then 'Connected' into the
frontend xenstore to complete my testing.

> Is my understanding right?

Yes. Obviously with a correctly functioning frontend (mine works
properly now) the bug in the backend should not become apparent, but if
the DomU ever crashed during the transition from backend Reconfiguring
to frontend Reconfiguring, then Dom0 would be affected so I think it is
worth fixing this bug. Also a malicious DomU could exploit this.



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