crypto: drbg - add async seeding operation

The async seeding operation is triggered during initalization right
after the first non-blocking seeding is completed. As required by the
asynchronous operation of random.c, a callback function is provided that
is triggered by random.c once entropy is available. That callback
function performs the actual seeding of the DRBG.

CC: Andreas Steffen <andreas.steffen@strongswan.org>
CC: Theodore Ts'o <tytso@mit.edu>
CC: Sandy Harris <sandyinchina@gmail.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/drbg.h

@@ -51,6 +51,7 @@
 #include <linux/fips.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
+#include <linux/workqueue.h>
 
 /*
  * Concatenation Helper and string operation helper
@@ -119,6 +120,7 @@ struct drbg_state {
 	bool fips_primed;	/* Continuous test primed? */
 	unsigned char *prev;	/* FIPS 140-2 continuous test value */
 #endif
+	struct work_struct seed_work;	/* asynchronous seeding support */
 	u8 *seed_buf;			/* buffer holding the seed */
 	size_t seed_buf_len;
 	const struct drbg_state_ops *d_ops;