perf evsel: Improve EPERM error handling in open_strerror()

We were showing a hardcoded default value for the kernel.perf_event_paranoid
sysctl, now that it became more paranoid (1 -> 2 [1]), this would need to be
updated, instead show the current value:

  [acme@jouet linux]$ perf record ls
  Error:
  You may not have permission to collect stats.

  Consider tweaking /proc/sys/kernel/perf_event_paranoid,
  which controls use of the performance events system by
  unprivileged users (without CAP_SYS_ADMIN).

  The current value is 2:

    -1: Allow use of (almost) all events by all users
  >= 0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
  >= 1: Disallow CPU event access by users without CAP_SYS_ADMIN
  >= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN
  [acme@jouet linux]$

[1] 0161028b7c8a ("perf/core: Change the default paranoia level to 2")

Reported-by: Ingo Molnar <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 738ce226002b8a0e88093fefaf74e9fe6093a13a..a5f339d447ccb6ec653d808175a200b39328370b 100644 (file)
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2382,12 +2382,13 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
                 "Consider tweaking /proc/sys/kernel/perf_event_paranoid,\n"
                 "which controls use of the performance events system by\n"
                 "unprivileged users (without CAP_SYS_ADMIN).\n\n"
-                "The default value is 1:\n\n"
+                "The current value is %d:\n\n"
                 "  -1: Allow use of (almost) all events by all users\n"
                 ">= 0: Disallow raw tracepoint access by users without CAP_IOC_LOCK\n"
                 ">= 1: Disallow CPU event access by users without CAP_SYS_ADMIN\n"
                 ">= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN",
-                                target->system_wide ? "system-wide " : "");
+                                target->system_wide ? "system-wide " : "",
+                                perf_event_paranoid());
        case ENOENT:
                return scnprintf(msg, size, "The %s event is not supported.",
                                 perf_evsel__name(evsel));