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random: simplify accounting logic

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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>
This commit is contained in:
Greg Price 2013-11-29 15:56:16 -05:00 committed by Theodore Ts'o
parent 19fa5be1d9
commit ee1de406ba
1 changed files with 4 additions and 8 deletions
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12
drivers/char/random.c
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@ -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;