Messages in this thread | | | Date | Thu, 25 Apr 2013 16:49:55 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH 05/14] perf tools: Introduce new 'ftrace' tool |
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On Thu, Apr 25, 2013 at 09:05:21AM -0400, Steven Rostedt wrote: > 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?
perf maintains backward compatibility, but not sure how far back it goes.. but as long as it's just writing -1 in here let's do that
jirka
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