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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>
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; ibytes = 0;
} else { } else {
/* If limited, never pull more than available */ /* If limited, never pull more than available */
if (r->limit && ibytes + reserved >= have_bytes) if (r->limit)
ibytes = have_bytes - reserved; ibytes = min_t(size_t, ibytes, have_bytes - reserved);
entropy_count = max_t(int, 0,
if (have_bytes >= ibytes + reserved) entropy_count - (ibytes << (ENTROPY_SHIFT + 3)));
entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
else
entropy_count = reserved << (ENTROPY_SHIFT + 3);
if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
goto retry; goto retry;