Re: Watching the libvirt RPC protocol using SystemTAP

[Mark Wielaard <mjw at redhat dot com>]

Hi Daniel,

On Wed, 2011-11-30 at 14:27 +0000, Daniel P. Berrange wrote:
> Trying again on Fedora 15, with systemtap 1.6, with just a short demo
> script
> 
> probe libvirt.rpc.client_msg_rx {
>   printf("client=%p len=%d program=%d version=%d procedure=%d type=%d status=%d serial=%d\n",
>          client, len, prog, vers, proc, type, status, serial);
>   print_ubacktrace();
> }
> 
> results in warnings and just a single hex symbol for backtrace
> 
> # stap demo1.stp
> WARNING: Couldn't register module '/usr/lib64/libvirt.so.0.9.7' for pid 6228 (-12)
> WARNING: Try increasing -DTASK_FINDER_VMA_ENTRY_ITEMS

Thanks for the short demo. (-12) is ENOMEM and this is
http://sourceware.org/bugzilla/show_bug.cgi?id=11671
"Allocate __stp_tf_vma_entry dynamically"

I hadn't given it very high priority because I thought it only occurred
in weird artificial situations. Clearly it does happen in practice, even
with a fairly simple setup. I'll give it higher priority.

BTW. The hard coded default for TASK_FINDER_VMA_ENTRY_ITEMS currently
is, the arbitrary number, 1536. You could try to do as the warning
message says and invoke stap with -DTASK_FINDER_VMA_ENTRY_ITEMS=7680 or
something even bigger to see if that helps.

Thanks,

Mark