[Patch v5 03/03]: hwrng: khwrngd derating per device

From: Torsten Duwe
Date: Tue May 27 2014 - 09:46:51 EST


This patch introduces a derating factor to struct hwrng for
the random bits going into the kernel input pool, and a common
default derating for drivers which do not specify one.

Signed-off-by: Torsten Duwe <duwe@xxxxxxx>

---
drivers/char/hw_random/core.c | 11 ++++++++++-
include/linux/hw_random.h | 3 +++
2 files changed, 13 insertions(+), 1 deletion(-)

--- linux/include/linux/hw_random.h.orig
+++ linux/include/linux/hw_random.h
@@ -29,6 +29,8 @@
* @read: New API. drivers can fill up to max bytes of data
* into the buffer. The buffer is aligned for any type.
* @priv: Private data, for use by the RNG driver.
+ * @quality: Estimation of true entropy in RNG's bitstream
+ * (per mill).
*/
struct hwrng {
const char *name;
@@ -38,6 +39,7 @@ struct hwrng {
int (*data_read)(struct hwrng *rng, u32 *data);
int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);
unsigned long priv;
+ unsigned short quality;

/* internal. */
struct list_head list;
--- linux/drivers/char/hw_random/core.c.orig
+++ linux/drivers/char/hw_random/core.c
@@ -56,11 +56,15 @@ static LIST_HEAD(rng_list);
static DEFINE_MUTEX(rng_mutex);
static int data_avail;
static u8 *rng_buffer, *rng_fillbuf;
-static unsigned short current_quality = 700; /* an arbitrary 70% */
+static unsigned short current_quality;
+static unsigned short default_quality = 0; /* default to "off" */

module_param(current_quality, ushort, 0644);
MODULE_PARM_DESC(current_quality,
"current hwrng entropy estimation per mill");
+module_param(default_quality, ushort, 0644);
+MODULE_PARM_DESC(default_quality,
+ "default entropy content of hwrng per mill");

static void start_khwrngd(void);

@@ -79,6 +83,11 @@ static inline int hwrng_init(struct hwrn
if (err)
return err;

+ current_quality = rng->quality ? : default_quality;
+ current_quality &= 1023;
+
+ if (current_quality == 0 && hwrng_fill)
+ kthread_stop(hwrng_fill);
if (current_quality > 0 && !hwrng_fill)
start_khwrngd();

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