Re: [win-pv-devel] XENIFACE not attaching to XENBUS

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: RafaÅ WojdyÅa [mailto:omeg@xxxxxxxxxxxxxxxxxxxxxx]
> Sent: 21 May 2015 04:56
> To: Paul Durrant; win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [win-pv-devel] XENIFACE not attaching to XENBUS
> 
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> On 2015-05-20 21:22, RafaÅ WojdyÅa wrote:
> > On 2015-05-20 20:53, RafaÅ WojdyÅa wrote:
> >> On 2015-05-20 16:15, Paul Durrant wrote:
> >>>> -----Original Message----- From:
> >>>> win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx
> >>>> [mailto:win-pv-devel- bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf
> >>>> Of Rafal Wojdyla Sent: 20 May 2015 11:05 To:
> >>>> win-pv-devel@xxxxxxxxxxxxxxxxxxxx Subject: [win-pv-devel]
> >>>> XENIFACE not attaching to XENBUS
> >>>>
> >>> Hello,
> >>>
> >>> I've noticed something strange when I was experimenting with
> >>> adding new APIs to Xenbus. I added a Store API to set key
> >>> permissions and incremented the store interface version as
> >>> usual (to 2 from 1).
> >
> > [...snip...]
> >
> >>>> However, since you did not modify the inf, xeniface should
> >>>> still be binding to revision 1 of the PDO and your log shows
> >>>>  that is still being created. The doc at
> >>>> https://msdn.microsoft.com/en-
> us/library/windows/hardware/ff539950%
> 28v=vs.85%29.aspx
> >>>>
> >>>>
> says that the maximum number is 64 and there are only 0x28 (40) in
> >>>> the list so the old compatible ID should still be there. You
> >>>>  should be able to check via device manager to make sure
> >>>> though.
> >
> > I think I've got it. We're hitting the other limit mentioned in
> > that MSDN page: "The maximum number of characters in a compatible
> > ID list, including a NULL terminator after each compatible ID and a
> > final NULL terminator, is REGSTR_VAL_MAX_HCID_LEN." This is 1024.
> > 1024/40 is 25, but our IDs are longer than that. I guess I'll
> > remove the oldest interface versions during testing until some
> > better solution is found. : )
> >
> I did some more tests and I'm still confused. With the same setup as
> above I added the latest PDO revision to XENIFACE's INF file:
> XENBUS\VEN_XS0001&DEV_IFACE&REV_00000028
> ...but it still didn't load. What's weird, registry and the device
> manager showed that this ID was indeed registered. It's probably
> related to the character limit I mentioned above because when I removed
> v1 and v2 interface versions from evtchn, it just started working again.
> 

Yes, it sounds like a buffer length limited to the length you state above. I 
guess we'll just need to retire some old interface versions (and put a check in 
to make sure we don't overflow the 1k limit).

  Paul

> - --
> RafaÅ WojdyÅa
> Qubes Tools for Windows developer
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