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

[Steven Rostedt <rostedt@goodmis.org>]

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.

-- Steve