tools lib fs: Add sysctl__read_int helper

Will come in handy for tools, see next patches.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
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-nay9j62ztxpytt4ew1tkl4op@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/fs/fs.c

@@ -184,3 +184,16 @@ int filename__read_int(const char *filename, int *value)
 	close(fd);
 	return err;
 }
+
+int sysctl__read_int(const char *sysctl, int *value)
+{
+	char path[PATH_MAX];
+	const char *procfs = procfs__mountpoint();
+
+	if (!procfs)
+		return -1;
+
+	snprintf(path, sizeof(path), "%s/sys/%s", procfs, sysctl);
+
+	return filename__read_int(path, value);
+}

tools/lib/api/fs/fs.h

@@ -13,4 +13,5 @@ const char *sysfs__mountpoint(void);
 const char *procfs__mountpoint(void);
 
 int filename__read_int(const char *filename, int *value);
+int sysctl__read_int(const char *sysctl, int *value);
 #endif /* __API_FS__ */