Re: how to register an event handler for the instance

[christopher lee <christopher.lee.eu@gmail.com>]

On Sat, 2022-05-07 at 08:02 +0300, Tzvetomir Stoyanov wrote:
> On Fri, May 6, 2022 at 7:18 PM christopher lee
> <christopher.lee.eu@gmail.com> wrote:
> > 
> > Hi all,
> > 
> > I use libtraceevent in my trace tool to parse the event log. Now I
> > allocated an instance, but no idea how to use
> > tep_register_event_handler() to register a handler for the
> > instance. Is
> > it possilbe to register handler for the event in the instance?
> > 
> 
> Hi Chrit,
> All trace events are the same across all trace instances, thus the
> handler registered with tep_register_event_handler() handles events
> from all instances with a given id. That's why there are no
> "instance"
> oriented APIs in that library. I would suggest looking at the tracefs
> library, which is instance aware. It can be used to allocate trace
> instances and read events from a given instance.
> 
> https://trace-cmd.org/Documentation/libtracefs/
> 


Hi Tzvetomir Stoyanov,

Thanks,  instance event handlers work now, but I'm confused with these
codes, do I have to read trace_pipe_raw? I found that if I didn't read
this file, the handler would not be able to get trace information.
Becuase if I read this file, and also call tep_print_event() will
consume lots of CPU resoruce. how can I parse the trace event info
without reading this file?
 

        for (i = 0; ; i++) {                                          
                char *raw_buf;                                        
                char *cpu;                                            
                                                                                                    
                ret = asprintf(&cpu, "%s/cpu%d", per_cpu, i);         
                if (ret < 0)                                          
                        pdie("Could not allocate memory for cpu buffer
%d name", i);                
                                                                                                    
                ret = stat(cpu, &st);                                 
                if (ret < 0 || !S_ISDIR(st.st_mode)) {                
                        free(cpu);                                    
                        goto start;                                   
                }                                                     
                                                                                                    
                ret = asprintf(&raw_buf, "%s/trace_pipe_raw", cpu);   
                if (ret < 0)                                          
                        pdie("Could not allocate memory for cpu %d raw
buffer name", i);            
                                                                                                    
                read_raw_buffer(i, raw_buf);                          
                free(raw_buf);                                        
                free(cpu);                                            
        } 

Best regards,
Christ

>