Re: [RFC PATCH v6 04/11] trace-cmd: Add buffer instance flags for tracing in guest and agent context

[Slavomir Kaslev <kaslevs@vmware.com>]

On Thu, Feb 14, 2019 at 03:05:20PM -0500, Steven Rostedt wrote:
> On Thu, 14 Feb 2019 16:13:28 +0200
> Slavomir Kaslev <kaslevs@vmware.com> wrote:
> 
> > Add BUFFER_FL_GUEST and BUFFER_FL_AGENT flags to differentiate when
> > trace-record.c is being called to trace guest or the VM tracing agent.
> > 
> > Also disable functions talking to the local tracefs when called in recording
> > guest instances context.
> > 
> > Signed-off-by: Slavomir Kaslev <kaslevs@vmware.com>
> > ---
> >  tracecmd/include/trace-local.h |  2 ++
> >  tracecmd/trace-record.c        | 55 ++++++++++++++++++++++++++++++++--
> >  2 files changed, 55 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
> > index a1a06e9..f19c8bb 100644
> > --- a/tracecmd/include/trace-local.h
> > +++ b/tracecmd/include/trace-local.h
> > @@ -149,6 +149,8 @@ char *strstrip(char *str);
> >  enum buffer_instance_flags {
> >  	BUFFER_FL_KEEP		= 1 << 0,
> >  	BUFFER_FL_PROFILE	= 1 << 1,
> > +	BUFFER_FL_GUEST		= 1 << 2,
> > +	BUFFER_FL_AGENT		= 1 << 3,
> >  };
> >  
> >  struct func_list {
> > diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> > index 8beefab..107d3d1 100644
> > --- a/tracecmd/trace-record.c
> > +++ b/tracecmd/trace-record.c
> > @@ -781,6 +781,9 @@ static void __clear_trace(struct buffer_instance *instance)
> >  	FILE *fp;
> >  	char *path;
> >  
> > +	if (instance->flags & BUFFER_FL_GUEST)
> > +		return;
> > +
> >  	/* reset the trace */
> >  	path = get_instance_file(instance, "trace");
> >  	fp = fopen(path, "w");
> > @@ -1264,6 +1267,9 @@ set_plugin_instance(struct buffer_instance *instance, const char *name)
> >  	char *path;
> >  	char zero = '0';
> >  
> > +	if (instance->flags & BUFFER_FL_GUEST)
> > +		return;
> > +
> >  	path = get_instance_file(instance, "current_tracer");
> >  	fp = fopen(path, "w");
> >  	if (!fp) {
> > @@ -1360,6 +1366,9 @@ static void disable_func_stack_trace_instance(struct buffer_instance *instance)
> >  	int size;
> >  	int ret;
> >  
> > +	if (instance->flags & BUFFER_FL_GUEST)
> > +		return;
> > +
> >  	path = get_instance_file(instance, "current_tracer");
> >  	ret = stat(path, &st);
> >  	tracecmd_put_tracing_file(path);
> 
> 
> I think we should add a:
> 
> #define is_guest(instance) ((instance)->flags & BUFFER_FL_GUEST)
> 
> Helper macro here, and all these should be turned into:
> 
> 	if (is_guest(instance))
> 		return;
> 
> Less error prone, and looks cleaner.
> 
> We could add a is_agent() too in later patches.

Makes sense. I added both is_agent and is_guest for the next iteration of this
patchset.