Messages in this thread | | | Subject | Re: [PATCH 05/14] perf tools: Introduce new 'ftrace' tool | From | Steven Rostedt <> | Date | Thu, 25 Apr 2013 09:05:21 -0400 |
| |
On Thu, 2013-04-25 at 18:51 +0900, Namhyung Kim wrote: > > > >> > >> Do you mean it should be changed to > >> > >> if (write_tracing_file("set_ftrace_pid", "-1") < 0) > >> > >> ? It seems it's the right thing to do for compatibility. > > > > > > looks like it's enough only to open it with O_TRUNC, > > so I guess whatever minimal goes write_tracing_file
Correct.
> > Yeah, but I can see below from trace-cmd code. > > trace-cmd/trace-record.c: > > /* > * Older kernels required "-1" to disable pid > */ > if (ret < 0 && !strlen(pid)) > ret = write(fd, "-1", 2); > > > Could you clarify this, Steve?
As the comment states, older kernels (before 2.6.33) required a -1. As trace-cmd is set up to work with at least 2.6.32, it requires the "-1" write. It doesn't hurt to have it.
But for perf ftrace (or whatever), I don't think we need the requirement to work with 2.6.32 kernels. Perf was added in 2.6.31, but do all functionalities still work that far back?
-- Steve
| |