perf tools: Handle EINTR error for readn/writen

Those readn/writen functions are to ensure read/write does I/O for
a given size exactly.  But ion() - its implementation - does not
handle in case it returns prematurely due to a signal.  As it's not
an error itself so just retry the operation.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1398346054-3322-1-git-send-email-namhyung@kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>

tools/perf/util/util.c

@@ -166,6 +166,8 @@ static ssize_t ion(bool is_read, int fd, void *buf, size_t n)
 		ssize_t ret = is_read ? read(fd, buf, left) :
 					write(fd, buf, left);
 
+		if (ret < 0 && errno == EINTR)
+			continue;
 		if (ret <= 0)
 			return ret;