random: simplify and rename credit_entropy_store

- emphasize bits in the name
- make zero bits lock-free
- simplify logic

Signed-off-by: Matt Mackall <mpm@selenic.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d33f52c..2faeef2 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -441,7 +441,7 @@ static struct entropy_store nonblocking_pool = {
 /*
  * This function adds bytes into the entropy "pool".  It does not
  * update the entropy estimate.  The caller should call
- * credit_entropy_store if this is appropriate.
+ * credit_entropy_bits if this is appropriate.
  *
  * The pool is stirred with a primitive polynomial of the appropriate
  * degree, and then twisted.  We twist by three bits at a time because
@@ -515,24 +515,22 @@ static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)
 /*
  * Credit (or debit) the entropy store with n bits of entropy
  */
-static void credit_entropy_store(struct entropy_store *r, int nbits)
+static void credit_entropy_bits(struct entropy_store *r, int nbits)
 {
        unsigned long flags;
 
+       if (!nbits)
+               return;
+
        spin_lock_irqsave(&r->lock, flags);
 
-       if (r->entropy_count + nbits < 0) {
-               DEBUG_ENT("negative entropy/overflow (%d+%d)\n",
-                         r->entropy_count, nbits);
+       DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
+       r->entropy_count += nbits;
+       if (r->entropy_count < 0) {
+               DEBUG_ENT("negative entropy/overflow\n");
                r->entropy_count = 0;
-       } else if (r->entropy_count + nbits > r->poolinfo->POOLBITS) {
+       } else if (r->entropy_count > r->poolinfo->POOLBITS)
                r->entropy_count = r->poolinfo->POOLBITS;
-       } else {
-               r->entropy_count += nbits;
-               if (nbits)
-                       DEBUG_ENT("added %d entropy credits to %s\n",
-                                 nbits, r->name);
-       }
 
        /* should we wake readers? */
        if (r == &input_pool && r->entropy_count >= random_read_wakeup_thresh)
@@ -619,8 +617,8 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
                 * Round down by 1 bit on general principles,
                 * and limit entropy entimate to 12 bits.
                 */
-               credit_entropy_store(&input_pool,
-                                    min_t(int, fls(delta>>1), 11));
+               credit_entropy_bits(&input_pool,
+                                   min_t(int, fls(delta>>1), 11));
        }
 out:
        preempt_enable();
@@ -702,7 +700,7 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
                bytes = extract_entropy(r->pull, tmp, bytes,
                                        random_read_wakeup_thresh / 8, rsvd);
                mix_pool_bytes(r, tmp, bytes);
-               credit_entropy_store(r, bytes*8);
+               credit_entropy_bits(r, bytes*8);
        }
 }
 
@@ -1073,7 +1071,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
                        return -EPERM;
                if (get_user(ent_count, p))
                        return -EFAULT;
-               credit_entropy_store(&input_pool, ent_count);
+               credit_entropy_bits(&input_pool, ent_count);
                return 0;
        case RNDADDENTROPY:
                if (!capable(CAP_SYS_ADMIN))
@@ -1088,7 +1086,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
                                    size);
                if (retval < 0)
                        return retval;
-               credit_entropy_store(&input_pool, ent_count);
+               credit_entropy_bits(&input_pool, ent_count);
                return 0;
        case RNDZAPENTCNT:
        case RNDCLEARPOOL: