crypto: cipher - introduce crypto_cipher_spawn and crypto_grab_cipher()

Currently, "cipher" (single-block cipher) spawns are usually initialized
by using crypto_get_attr_alg() to look up the algorithm, then calling
crypto_init_spawn().  In one case, crypto_grab_spawn() is used directly.

The former way is different from how skcipher, aead, and akcipher spawns
are initialized (they use crypto_grab_*()), and for no good reason.
This difference introduces unnecessary complexity.

The crypto_grab_*() functions used to have some problems, like not
holding a reference to the algorithm and requiring the caller to
initialize spawn->base.inst.  But those problems are fixed now.

Also, the cipher spawns are not strongly typed; e.g., the API requires
that the user manually specify the flags CRYPTO_ALG_TYPE_CIPHER and
CRYPTO_ALG_TYPE_MASK.  Though the "cipher" algorithm type itself isn't
yet strongly typed, we can start by making the spawns strongly typed.

So, let's introduce a new 'struct crypto_cipher_spawn', and functions
crypto_grab_cipher() and crypto_drop_cipher() to grab and drop them.

Later patches will convert all cipher spawns to use these, then make
crypto_spawn_cipher() take 'struct crypto_cipher_spawn' as well, instead
of a bare 'struct crypto_spawn' as it currently does.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/algapi.h

@@ -208,6 +208,31 @@ static inline void *crypto_instance_ctx(struct crypto_instance *inst)
 	return inst->__ctx;
 }
 
+struct crypto_cipher_spawn {
+	struct crypto_spawn base;
+};
+
+static inline int crypto_grab_cipher(struct crypto_cipher_spawn *spawn,
+				     struct crypto_instance *inst,
+				     const char *name, u32 type, u32 mask)
+{
+	type &= ~CRYPTO_ALG_TYPE_MASK;
+	type |= CRYPTO_ALG_TYPE_CIPHER;
+	mask |= CRYPTO_ALG_TYPE_MASK;
+	return crypto_grab_spawn(&spawn->base, inst, name, type, mask);
+}
+
+static inline void crypto_drop_cipher(struct crypto_cipher_spawn *spawn)
+{
+	crypto_drop_spawn(&spawn->base);
+}
+
+static inline struct crypto_alg *crypto_spawn_cipher_alg(
+	struct crypto_cipher_spawn *spawn)
+{
+	return spawn->base.alg;
+}
+
 static inline struct crypto_cipher *crypto_spawn_cipher(
 	struct crypto_spawn *spawn)
 {