perf tools: Introduce filename__read_int helper

Just opens a file and calls atoi() in at most its first 64 bytes.

To read things like /proc/sys/kernel/perf_event_paranoid.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-669q04c5tou5pnt8jtiz6y2r@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 19 insertions, 0 deletions

diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 8dc8cf39f4ed..c25e57b3acb2 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -394,3 +394,20 @@ unsigned long parse_tag_value(const char *str, struct parse_tag *tags)
 
         return (unsigned long) -1;
 }
+
+int filename__read_int(const char *filename, int *value)
+{
+        char line[64];
+        int fd = open(filename, O_RDONLY), err = -1;
+
+        if (fd < 0)
+                return -1;
+
+        if (read(fd, line, sizeof(line)) > 0) {
+                *value = atoi(line);
+                err = 0;
+        }
+
+        close(fd);
+        return err;
+}
diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
index 42dfba70fbfc..c8f362daba87 100644
--- a/tools/perf/util/util.h
+++ b/tools/perf/util/util.h
@@ -305,4 +305,6 @@ struct dso;
 
 char *get_srcline(struct dso *dso, unsigned long addr);
 void free_srcline(char *srcline);
+
+int filename__read_int(const char *filename, int *value);
 #endif /* GIT_COMPAT_UTIL_H */