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/**
* Watch available kernel entropy. By default, it prints the available entropy
* and difference to the previously recorded entropy every second, but this can
* be changed with arg1 (in milliseconds). You can also press Enter to
* immediately print the current entropy.
*
* 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;
long int avail, prev = 0;
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) {
/* remove possible newline and terminate string for sure */
buff[r - 1] = 0;
avail = strtol(buff, NULL, 10);
printf("%li (%+li)", avail, avail - prev);
fflush(stdout);
prev = avail;
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;
}
putchar('\n');
}
close(fd);
return 0;
}
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