+static int ahash_save_req(struct ahash_request *req, crypto_completion_t cplt)
+{
+ struct crypto_ahash *tfm = crypto_ahash_reqtfm(req);
+ unsigned long alignmask = crypto_ahash_alignmask(tfm);
+ unsigned int ds = crypto_ahash_digestsize(tfm);
+ struct ahash_request_priv *priv;
+
+ priv = kmalloc(sizeof(*priv) + ahash_align_buffer_size(ds, alignmask),
+ (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ?
+ GFP_KERNEL : GFP_ATOMIC);
+ if (!priv)
+ return -ENOMEM;
+
+ /*
+ * WARNING: Voodoo programming below!
+ *
+ * The code below is obscure and hard to understand, thus explanation
+ * is necessary. See include/crypto/hash.h and include/linux/crypto.h
+ * to understand the layout of structures used here!
+ *
+ * The code here will replace portions of the ORIGINAL request with
+ * pointers to new code and buffers so the hashing operation can store
+ * the result in aligned buffer. We will call the modified request
+ * an ADJUSTED request.
+ *
+ * The newly mangled request will look as such:
+ *
+ * req {
+ * .result = ADJUSTED[new aligned buffer]
+ * .base.complete = ADJUSTED[pointer to completion function]
+ * .base.data = ADJUSTED[*req (pointer to self)]
+ * .priv = ADJUSTED[new priv] {
+ * .result = ORIGINAL(result)
+ * .complete = ORIGINAL(base.complete)
+ * .data = ORIGINAL(base.data)
+ * }
+ */
+
+ priv->result = req->result;
+ priv->complete = req->base.complete;
+ priv->data = req->base.data;
+ /*
+ * WARNING: We do not backup req->priv here! The req->priv
+ * is for internal use of the Crypto API and the
+ * user must _NOT_ _EVER_ depend on it's content!
+ */
+
+ req->result = PTR_ALIGN((u8 *)priv->ubuf, alignmask + 1);
+ req->base.complete = cplt;
+ req->base.data = req;
+ req->priv = priv;
+
+ return 0;
+}
+
+static void ahash_restore_req(struct ahash_request *req)
+{
+ struct ahash_request_priv *priv = req->priv;
+
+ /* Restore the original crypto request. */
+ req->result = priv->result;
+ req->base.complete = priv->complete;
+ req->base.data = priv->data;
+ req->priv = NULL;
+
+ /* Free the req->priv.priv from the ADJUSTED request. */
+ kzfree(priv);
+}
+