+/* Generate the Redis "Run ID", a SHA1-sized random number that identifies a
+ * given execution of Redis, so that if you are talking with an instance
+ * having run_id == A, and you reconnect and it has run_id == B, you can be
+ * sure that it is either a different instance or it was restarted. */
+void getRandomHexChars(char *p, unsigned int len) {
+ FILE *fp = fopen("/dev/urandom","r");
+ char *charset = "0123456789abcdef";
+ unsigned int j;
+
+ if (fp == NULL || fread(p,len,1,fp) == 0) {
+ /* If we can't read from /dev/urandom, do some reasonable effort
+ * in order to create some entropy, since this function is used to
+ * generate run_id and cluster instance IDs */
+ char *x = p;
+ unsigned int l = len;
+ struct timeval tv;
+ pid_t pid = getpid();
+
+ /* Use time and PID to fill the initial array. */
+ gettimeofday(&tv,NULL);
+ if (l >= sizeof(tv.tv_usec)) {
+ memcpy(x,&tv.tv_usec,sizeof(tv.tv_usec));
+ l -= sizeof(tv.tv_usec);
+ x += sizeof(tv.tv_usec);
+ }
+ if (l >= sizeof(tv.tv_sec)) {
+ memcpy(x,&tv.tv_sec,sizeof(tv.tv_sec));
+ l -= sizeof(tv.tv_sec);
+ x += sizeof(tv.tv_sec);
+ }
+ if (l >= sizeof(pid)) {
+ memcpy(x,&pid,sizeof(pid));
+ l -= sizeof(pid);
+ x += sizeof(pid);
+ }
+ /* Finally xor it with rand() output, that was already seeded with
+ * time() at startup. */
+ for (j = 0; j < len; j++)
+ p[j] ^= rand();
+ }
+ /* Turn it into hex digits taking just 4 bits out of 8 for every byte. */
+ for (j = 0; j < len; j++)
+ p[j] = charset[p[j] & 0x0F];
+ fclose(fp);
+}
+