random: simplify loop in random_read

The loop condition never changes until just before a break, so we
might as well write it as a constant.  Also since a996996d
("random: drop weird m_time/a_time manipulation") we don't do anything
after the loop finishes, so the 'break's might as well return
directly.  Some other simplifications.

There should be no change in behavior introduced by this commit.
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

drivers/char/random.c

@@ -1285,53 +1285,32 @@ void rand_initialize_disk(struct gendisk *disk)
 static ssize_t
 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 {
-	ssize_t n, retval = 0, count = 0;
+	ssize_t n;
 
 	if (nbytes == 0)
 		return 0;
 
-	while (nbytes > 0) {
-		n = nbytes;
-		if (n > SEC_XFER_SIZE)
-			n = SEC_XFER_SIZE;
-
-		n = extract_entropy_user(&blocking_pool, buf, n);
-
-		if (n < 0) {
-			retval = n;
-			break;
-		}
-
+	nbytes = min_t(size_t, nbytes, SEC_XFER_SIZE);
+	while (1) {
+		n = extract_entropy_user(&blocking_pool, buf, nbytes);
+		if (n < 0)
+			return n;
 		trace_random_read(n*8, (nbytes-n)*8,
 				  ENTROPY_BITS(&blocking_pool),
 				  ENTROPY_BITS(&input_pool));
-
-		if (n == 0) {
-			if (file->f_flags & O_NONBLOCK) {
-				retval = -EAGAIN;
-				break;
-			}
-
-			wait_event_interruptible(random_read_wait,
-				ENTROPY_BITS(&input_pool) >=
-				random_read_wakeup_thresh);
-
-			if (signal_pending(current)) {
-				retval = -ERESTARTSYS;
-				break;
-			}
-
-			continue;
-		}
-
-		count += n;
-		buf += n;
-		nbytes -= n;
-		break;		/* This break makes the device work */
-				/* like a named pipe */
+		if (n > 0)
+			return n;
+		/* Pool is (near) empty.  Maybe wait and retry. */
+
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		wait_event_interruptible(random_read_wait,
+			ENTROPY_BITS(&input_pool) >=
+			random_read_wakeup_thresh);
+		if (signal_pending(current))
+			return -ERESTARTSYS;
 	}
-
-	return (count ? count : retval);
 }
 
 static ssize_t