random: simplify accounting logic

This logic is exactly equivalent to the old logic, but it should
be easier to see what it's doing.

The equivalence depends on one fact from outside this function:
when 'r->limit' is false, 'reserved' is zero.  (Well, two facts;
the other is that 'reserved' is never negative.)

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2c532a6b0a219f53244ee0ef2c0fdb08195027e8..9675821b4b5af05b7c057e90603b329d5232392b 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -984,14 +984,10 @@ retry:
                ibytes = 0;
        } else {
                /* If limited, never pull more than available */
-               if (r->limit && ibytes + reserved >= have_bytes)
-                       ibytes = have_bytes - reserved;
-
-               if (have_bytes >= ibytes + reserved)
-                       entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
-               else
-                       entropy_count = reserved << (ENTROPY_SHIFT + 3);
-
+               if (r->limit)
+                       ibytes = min_t(size_t, ibytes, have_bytes - reserved);
+               entropy_count = max_t(int, 0,
+                           entropy_count - (ibytes << (ENTROPY_SHIFT + 3)));
                if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
                        goto retry;