[PATCH 08/11] random: simplify accounting logic

[Greg Price <price@MIT.EDU>]

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.)

Which is a good thing, too, because the "entropy_count = reserved"
line would have had a bug otherwise -- 'reserved' counts bytes and
'entropy_count' counts bits.  Fortunately that line could only be
reached if 'r->limit' was false, and zero bytes is zero bits.

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Price <price@mit.edu>
---
 drivers/char/random.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 8824e8d..9e4645e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -860,12 +860,7 @@ retry:
 		/* If limited, never pull more than available */
 		if (r->limit)
 			nbytes = min_t(size_t, nbytes, entropy_count/8 - reserved);
-
-		if (entropy_count / 8 >= nbytes + reserved) {
-			entropy_count -= nbytes*8;
-		} else {
-			entropy_count = reserved;
-		}
+		entropy_count = max_t(int, entropy_count - nbytes*8, 0);
 		if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
 			goto retry;
 
-- 
1.8.3.2