Add random entropy watcher

1 files changed, 55 insertions, 0 deletions

diff --git a/entropy-watcher.c b/entropy-watcher.c
new file mode 100644
index 0000000..2d6fe86
--- /dev/null
+++ b/entropy-watcher.c
@@ -0,0 +1,55 @@
+/**
+ * Watch available kernel entropy. By default, it prints the available entrophy
+ * every second, but this can be changed with arg1 (in milliseconds). You can
+ * also press Enter to immediately print the current entrophy.
+ *
+ * Author: Peter Wu <lekensteyn@gmail.com>
+ * Date: 2013-01-28
+ */
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <poll.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#define FILENAME "/proc/sys/kernel/random/entropy_avail"
+
+int main(int argc, char **argv) {
+	char buff[32];
+	ssize_t r;
+	struct pollfd pfd;
+	int fd;
+	int print_interval_ms;
+
+	print_interval_ms = 1000;
+	if (argc > 1) {
+		print_interval_ms = atoi(argv[1]);
+	}
+
+	fd = open(FILENAME, O_RDONLY);
+	if (fd < 0) {
+		perror(FILENAME);
+		return 1;
+	}
+
+	pfd.fd = STDIN_FILENO;
+	pfd.events = POLLIN;
+
+	while ((r = read(fd, buff, sizeof(buff))) > 0) {
+		write(STDOUT_FILENO, buff, r - 1);
+		poll(&pfd, 1, print_interval_ms);
+		lseek(fd, 0, SEEK_SET);
+		if (pfd.revents == POLLIN) { /* pressed enter? */
+			r = read(STDIN_FILENO, buff, sizeof(buff));
+			if (r > 0 && buff[r - 1] == '\n')
+				continue;
+		}
+		buff[0] = '\n';
+		write(STDOUT_FILENO, buff, 1);
+	}
+
+	close(fd);
+
+	return 0;
+}