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Subject[PATCH 03/14] random: reserve for /dev/random only once /dev/urandom seeded
Early in boot, we really want to make sure the nonblocking pool (for
/dev/urandom and the kernel's own use) gets an adequate amount of
entropy ASAP. Anyone reading /dev/random is prepared to wait
potentially a long time anyway, so delaying them a little bit more at
boot until /dev/urandom is seeded is no big deal. This logic still
ensures that /dev/random readers won't starve indefinitely.

At present most input goes directly to the nonblocking pool early on
anyway, but this helps put us in a position to change that.

Signed-off-by: Greg Price <price@mit.edu>
---
drivers/char/random.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 92d9f6862..bf7fedadd 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -923,19 +923,21 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
{
__u32 tmp[OUTPUT_POOL_WORDS];
- int bytes, min_bytes;
-
- /* For /dev/random's pool, always leave two wakeups' worth */
- int rsvd_bytes = r->limit ? 0 : random_read_wakeup_bits / 4;
+ int bytes, min_bytes, reserved_bytes;

/* pull at least as much as a wakeup */
min_bytes = random_read_wakeup_bits / 8;
/* but never more than the buffer size */
bytes = min(sizeof(tmp), max_t(size_t, min_bytes, nbytes));

+ /* reserve some for /dev/random's pool, unless we really need it */
+ reserved_bytes = 0;
+ if (!r->limit && r->initialized)
+ reserved_bytes = 2 * (random_read_wakeup_bits / 8);
+
trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8,
ENTROPY_BITS(r), ENTROPY_BITS(r->pull));
- bytes = extract_entropy(r->pull, tmp, bytes, min_bytes, rsvd_bytes);
+ bytes = extract_entropy(r->pull, tmp, bytes, min_bytes, reserved_bytes);
mix_pool_bytes(r, tmp, bytes, NULL);
credit_entropy_bits(r, bytes*8);
}
--
1.8.3.2


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