• Steven Rostedt's avatar
    tracing: Let tracepoints have data passed to tracepoint callbacks · 38516ab5
    Steven Rostedt authored
    This patch adds data to be passed to tracepoint callbacks.
    
    The created functions from DECLARE_TRACE() now need a mandatory data
    parameter. For example:
    
    DECLARE_TRACE(mytracepoint, int value, value)
    
    Will create the register function:
    
    int register_trace_mytracepoint((void(*)(void *data, int value))probe,
                                    void *data);
    
    As the first argument, all callbacks (probes) must take a (void *data)
    parameter. So a callback for the above tracepoint will look like:
    
    void myprobe(void *data, int value)
    {
    }
    
    The callback may choose to ignore the data parameter.
    
    This change allows callbacks to register a private data pointer along
    with the function probe.
    
    	void mycallback(void *data, int value);
    
    	register_trace_mytracepoint(mycallback, mydata);
    
    Then the mycallback() will receive the "mydata" as the first parameter
    before the args.
    
    A more detailed example:
    
      DECLARE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status));
    
      /* In the C file */
    
      DEFINE_TRACE(mytracepoint, TP_PROTO(int status), TP_ARGS(status));
    
      [...]
    
           trace_mytracepoint(status);
    
      /* In a file registering this tracepoint */
    
      int my_callback(void *data, int status)
      {
    	struct my_struct my_data = data;
    	[...]
      }
    
      [...]
    	my_data = kmalloc(sizeof(*my_data), GFP_KERNEL);
    	init_my_data(my_data);
    	register_trace_mytracepoint(my_callback, my_data);
    
    The same callback can also be registered to the same tracepoint as long
    as the data registered is different. Note, the data must also be used
    to unregister the callback:
    
    	unregister_trace_mytracepoint(my_callback, my_data);
    
    Because of the data parameter, tracepoints declared this way can not have
    no args. That is:
    
      DECLARE_TRACE(mytracepoint, TP_PROTO(void), TP_ARGS());
    
    will cause an error.
    
    If no arguments are needed, a new macro can be used instead:
    
      DECLARE_TRACE_NOARGS(mytracepoint);
    
    Since there are no arguments, the proto and args fields are left out.
    
    This is part of a series to make the tracepoint footprint smaller:
    
       text	   data	    bss	    dec	    hex	filename
    4913961	1088356	 861512	6863829	 68bbd5	vmlinux.orig
    4914025	1088868	 861512	6864405	 68be15	vmlinux.class
    4918492	1084612	 861512	6864616	 68bee8	vmlinux.tracepoint
    
    Again, this patch also increases the size of the kernel, but
    lays the ground work for decreasing it.
    
     v5: Fixed net/core/drop_monitor.c to handle these updates.
    
     v4: Moved the DECLARE_TRACE() DECLARE_TRACE_NOARGS out of the
         #ifdef CONFIG_TRACE_POINTS, since the two are the same in both
         cases. The __DECLARE_TRACE() is what changes.
         Thanks to Frederic Weisbecker for pointing this out.
    
     v3: Made all register_* functions require data to be passed and
         all callbacks to take a void * parameter as its first argument.
         This makes the calling functions comply with C standards.
    
         Also added more comments to the modifications of DECLARE_TRACE().
    
     v2: Made the DECLARE_TRACE() have the ability to pass arguments
         and added a new DECLARE_TRACE_NOARGS() for tracepoints that
         do not need any arguments.
    Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Acked-by: default avatarMasami Hiramatsu <mhiramat@redhat.com>
    Acked-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Cc: Neil Horman <nhorman@tuxdriver.com>
    Cc: David S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    38516ab5
trace_syscalls.c 13.8 KB