linux-kernel - [PATCH 6/9] random: simplify accounting logic

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Message-ID: <20131113080821.GT16018@ringworld.MIT.EDU>
Date:	Wed, 13 Nov 2013 03:08:21 -0500
From:	Greg Price <price@....EDU>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 6/9] 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: "Theodore Ts'o" <tytso@....edu>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Greg Price <price@....edu>
---
 drivers/char/random.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index fe7ecdd..5dffca8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -988,14 +988,10 @@ 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;
 
-- 
1.8.3.2

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