Re: [Qemu-devel] [PATCH v2] Add a DTrace tracing backend targetted for SystemTAP compatability

["Daniel P. Berrange" <berrange@redhat.com>]

On Wed, Oct 27, 2010 at 12:26:50PM +0530, Prerna Saxena wrote:
> ACK, works well!
> A suggestion though..
> 
> On 10/20/2010 07:39 PM, Daniel P. Berrange wrote:
> >
> >eg, instead of
> >
> >   probe process("qemu").mark("qemu_malloc") {
> >     printf("Malloc %d %p\n", $arg1, $arg2);
> >   }
> >
> >The addition of qemu.stp to /usr/share/systemtap/tapset/
> >lets users write
> >
> >   probe qemu.qemu_malloc {
> >     printf("Malloc %d %p\n", size, ptr);
> >   }
> >...
> >
> >
> >diff --git a/tracetool b/tracetool
> >index 7010858..047f16b 100755
> >--- a/tracetool
> >+++ b/tracetool
> >+linetos_dtrace()
> >+{
> >+    local name args arglist state
> >+
> >+    # Define prototype for probe arguments
> >+    cat<<EOF
> >+probe qemu.$name = process("qemu").mark("$name")
> >+{
> 
> The 'process' probes only work by looking for the binary in $PATH, 
> unless the full path is specified. When compiling qemu in non-standard 
> locations ( ie with --prefix), such probes would not point to the 
> correct binary. It could be nice if tracetool could pass the full build 
> path for defining the probe point. Eg,
> 
> probe qemu.qemu_malloc = 
> process("/Path/to/build/dir/bin/qemu").mark("qemu_malloc") { .. }

Yes, that's doable. The other problem with this tapset is that it
only works for the 'qemu' binary and not the 'qemu-system-XXXX'
binaries. I either need to make the probe cover all binaries, or
generate one tapset per architecture target.  I'm going to split
this patch in 2, one with just the core dtrace bits, and a second
with the systemtap tapset addon.

Regards,
Daniel
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