[Xen-users] tbctl and setsize errors and weirdness...

[Kaleb Pederson <kibab@xxxxxxxxxxxx>]

Hello,

If I have understood everything correctly based on my reading, google, etc. 
`tbctl 1` should turn on the trace buffer, and then `setsize N` should 
allocate N pages for the trace buffer.  Yet for some reason, after a reboot, 
tbctl seems to require that I allocate space with setsize first, even though 
setsize appears to error out.

Here's the transcript on my box, running xen-3.0.2:

# after a reboot, not having yet run tbctl or setsize (xend running)
kibab conf # tbctl 1
Enable/Disable Hypercall failure: Invalid argument

# a second attempt
kibab conf # tbctl 1
Enable/Disable Hypercall failure: Invalid argument

# call setsize, even though the trace buffer hasn't yet been turned on...
kibab conf # setsize 10
Failure to get tbuf info from Xen. Guess size is 0: Invalid argument
This may mean that tracing is not enabled in xen.
set_size succeeded.
Failure to get tbuf info from Xen. Tracing must be enabled first: Invalid 
argument

# ok, so the setsize call failed ... didn't it??
kibab conf # tbctl 1
Tracing now enabled

# strange... it worked last time
kibab conf # setsize 10
Current tbuf size: 0xa000
set_size Hypercall failure: Invalid argument

# ok, was that 0xa000 caused by me?
kibab conf # setsize 20
Current tbuf size: 0xa000
set_size Hypercall failure: Invalid argument

# see if it changed anything
kibab conf # setsize 10
Current tbuf size: 0xa000
set_size Hypercall failure: Invalid argument

The code for both is simple, but I'm not familiar with the underlying API 
calls to know what's wrong.  Suggestions?  How can we fix it?

Thanks.

--Kaleb

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