On 10/3/13 6:38 AM, Ingo Molnar wrote:
* Ramkumar Ramachandra <[email protected]> wrote:+ /* Perform a quick sanity check */ + if (!is_valid_tracepoint("power:cpu_frequency")) { + fprintf(stderr, "Error:\tNo permissions to read $debugfs/tracing/events/power/cpu_frequency\n"); + fprintf(stderr, "Hint:\tChange the permissions of debugfs: /sys/kernel/debug\n"); + fprintf(stderr, "\tThe directory will be present if your kernel was compiled with debugfs support.\n");Is missing permissions the only way how is_valid_tracepoint() can fail? What if debugfs has the right permissions but CONFIG_TRACEPOINTS is disabled in the kernel?
There are a number of reasons that function can fail. The complete solution is to plumb various error numbers and on failure request a string for that failure. Take a look at util/target.[ch] as an example.
The comment applies to the perf-trace patch as well, but it gets more complicated to handle the error paths from perf_evsel__newtp when they dip into the tracepoint code
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