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>

1 files changed, 15 insertions, 17 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d33f52cd437b..2faeef28c209 100644
--- 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: