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Merge pull request #86 from llvilanova/patch/perf-perms

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perf: Be more informative about errors with perf's permissions
This commit is contained in:
Charlie Curtsinger 2016-11-22 18:18:49 -06:00 committed by GitHub
commit 913b76898e
1 changed files with 18 additions and 1 deletions
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19
libcoz/perf.cpp
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@ -54,7 +54,24 @@ perf_event::perf_event(struct perf_event_attr& pe, pid_t pid, int cpu) :
// Open the file
_fd = perf_event_open(&pe, pid, cpu, -1, 0);
REQUIRE(_fd != -1) << "Failed to open perf event";
if (_fd == -1) {
std::string path = "/proc/sys/kernel/perf_event_paranoid";
FILE *file = fopen(path.c_str(), "r");
REQUIRE(file != NULL) << "Failed to open " << path << ": " << strerror(errno);
char value_str[3];
int res = fread(value_str, sizeof(value_str), 1, file);
REQUIRE(res != -1) << "Failed to read from " << path << ": " << strerror(errno);
value_str[2] = '\0';
int value = atoi(value_str);
FATAL << "Failed to open perf event. "
<< "Consider tweaking " << path << " to 2 or less "
<< "(current value is " << value << "), "
<< "or run coz as a privileged user (with CAP_SYS_ADMIN).";
}
// If sampling, map the perf event file
if(pe.sample_type != 0 && pe.sample_period != 0) {