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" <ty...@mit.edu>
Cc: Jiri Kosina <jkos...@suse.cz>
Signed-off-by: Greg Price <pr...@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
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