[2/4] crypto: Introduce some helper functions to help to merge requests

diff --git a/crypto/ablk_helper.c b/crypto/ablk_helper.c
index e1fcf53..3cf15cb 100644
--- a/crypto/ablk_helper.c
+++ b/crypto/ablk_helper.c
@@ -26,6 +26,7 @@ 
 
 #include <linux/kernel.h>
 #include <linux/crypto.h>
+#include <linux/device-mapper.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/hardirq.h>
@@ -34,6 +35,140 @@ 
 #include <crypto/ablk_helper.h>
 #include <asm/simd.h>
 
+/**
+ * ablk_link_request_if_contigous - try to link one request into previous one
+ * if the page address is contiguous.
+ * @list_req: the request from queue list
+ * @req: the new request need to be merged
+ *
+ * If the listed request and new request's pages of the scatterlists are
+ * contiguous, then merge the scatterlists of new request into the listed one.
+ *
+ * Return true on success, others means failed.
+ */
+static bool ablk_link_request_if_contigous(struct ablkcipher_request *list_req,
+					   struct ablkcipher_request *req)
+{
+	struct scatterlist *last_src_sg =
+		sg_last(list_req->sgt_src.sgl, list_req->sgt_src.nents);
+	struct scatterlist *last_dst_sg =
+		sg_last(list_req->sgt_dst.sgl, list_req->sgt_dst.nents);
+	struct scatterlist *req_src_sg = req->src;
+	struct scatterlist *req_dst_sg = req->dst;
+
+	if (!last_src_sg || !last_dst_sg)
+		return false;
+
+	/* Check if the src/dst scatterlists are contiguous */
+	if (!sg_is_contiguous(last_src_sg, req_src_sg) ||
+	    !sg_is_contiguous(last_dst_sg, req_dst_sg))
+		return false;
+
+	/*
+	 * If the request can be merged into the listed request after the
+	 * checking, then expand the listed request scatterlists' length.
+	 */
+	last_src_sg->length += req_src_sg->length;
+	last_dst_sg->length += req_dst_sg->length;
+	list_req->nbytes += req->nbytes;
+
+	return true;
+}
+
+/**
+ * ablk_merge_request - try to merge one request into previous one
+ * @list_req: the request from queue list
+ * @req: the request need to be merged
+ *
+ * This function will create a dynamic scatterlist table for both source
+ * and destination if the request is the first coming in.
+ *
+ * Return true on success, others means failed.
+ */
+static bool ablk_merge_request(struct ablkcipher_request *list_req,
+			       struct ablkcipher_request *req)
+{
+	struct sg_table *sgt_src = &list_req->sgt_src;
+	struct sg_table *sgt_dst = &list_req->sgt_dst;
+	unsigned int nents = SG_MAX_SINGLE_ALLOC;
+
+	if (sg_table_is_empty(sgt_src)) {
+		if (sg_alloc_empty_table(sgt_src, nents, GFP_ATOMIC))
+			return false;
+
+		if (sg_add_sg_to_table(sgt_src, list_req->src))
+			return false;
+	}
+
+	if (sg_table_is_empty(sgt_dst)) {
+		if (sg_alloc_empty_table(sgt_dst, nents, GFP_ATOMIC))
+			return false;
+
+		if (sg_add_sg_to_table(sgt_dst, list_req->dst))
+			return false;
+	}
+
+	/*
+	 * Check if the new request is contiguous for the listed request,
+	 * if it is contiguous then merge the new request into the listed one.
+	 */
+	if (ablk_link_request_if_contigous(list_req, req))
+		return true;
+
+	if (sg_add_sg_to_table(sgt_src, req->src))
+		return false;
+
+	if (sg_add_sg_to_table(sgt_dst, req->dst))
+		return false;
+
+	list_req->nbytes += req->nbytes;
+	return true;
+}
+
+/**
+ * ablk_try_merge - try to merge one request into previous one
+ * @queue: the crypto queue list
+ * @req: the request need to be merged
+ *
+ * Note: The merging action should be under the spinlock or mutex protection.
+ *
+ * Return 0 on success and others are failed.
+ */
+int ablk_try_merge(struct crypto_queue *queue,
+		   struct ablkcipher_request *req)
+{
+	struct ablkcipher_request *list_req;
+	struct crypto_async_request *async_req;
+
+	list_for_each_entry(async_req, &queue->list, list) {
+		list_req = ablkcipher_request_cast(async_req);
+
+		if (list_req->base.flags != req->base.flags)
+			continue;
+
+		/* Check that the request adds up to an even number of sectors */
+		if (!IS_ALIGNED(list_req->nbytes, (1U << SECTOR_SHIFT)))
+			continue;
+
+		if (list_req->nbytes + req->nbytes > UINT_MAX)
+			continue;
+
+		/*
+		 * We first check that the sectors are adjacent so we don't
+		 * mistadly coalesce something that is contigous in memory but
+		 * not contigous on disk.
+		 */
+		if (list_req->sector + list_req->nbytes /
+		    (1U << SECTOR_SHIFT) == req->sector) {
+			if (ablk_merge_request(list_req, req))
+				return 0;
+		}
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(ablk_try_merge);
+
 int ablk_set_key(struct crypto_ablkcipher *tfm, const u8 *key,
 		 unsigned int key_len)
 {
diff --git a/include/crypto/ablk_helper.h b/include/crypto/ablk_helper.h
index 4f93df5..12ae00d 100644
--- a/include/crypto/ablk_helper.h
+++ b/include/crypto/ablk_helper.h
@@ -8,6 +8,7 @@ 
 #include <linux/crypto.h>
 #include <linux/kernel.h>
 #include <crypto/cryptd.h>
+#include <crypto/algapi.h>
 
 struct async_helper_ctx {
 	struct cryptd_ablkcipher *cryptd_tfm;
@@ -28,4 +29,6 @@  extern int ablk_init_common(struct crypto_tfm *tfm, const char *drv_name);
 
 extern int ablk_init(struct crypto_tfm *tfm);
 
+extern int ablk_try_merge(struct crypto_queue *queue,
+			  struct ablkcipher_request *req);
 #endif /* _CRYPTO_ABLK_HELPER_H */
diff --git a/include/linux/crypto.h b/include/linux/crypto.h
index e71cb70..f878bb1 100644
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -21,6 +21,7 @@ 
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/bug.h>
+#include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>
@@ -170,6 +171,10 @@  struct ablkcipher_request {
 	struct scatterlist *src;
 	struct scatterlist *dst;
 
+	struct sg_table sgt_src;
+	struct sg_table sgt_dst;
+	sector_t	sector;
+
 	void *__ctx[] CRYPTO_MINALIGN_ATTR;
 };