We add a new @unit_size data member to struct acomp_req along with a
helper function acomp_request_set_unit_size() for kernel modules to set
the unit size to use while breaking down the request's src/dst
scatterlists.

An acomp_alg can implement batching by using the @req->unit_size to
break down the SG lists passed in via @req->dst and/or @req->src, to
submit individual @req->slen/@req->unit_size compress jobs or
@req->dlen/@req->unit_size decompress jobs, for batch compression and
batch decompression respectively.

In case of batch compression, the folio's pages for the batch can be
retrieved from the @req->src scatterlist by using an struct sg_page_iter
after determining the number of pages as @req->slen/@req->unit_size.

Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
 include/crypto/acompress.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/crypto/acompress.h b/include/crypto/acompress.h
index 9eacb9fa375d..0f1334168f1b 100644
--- a/include/crypto/acompress.h
+++ b/include/crypto/acompress.h
@@ -79,6 +79,7 @@ struct acomp_req_chain {
  * @dvirt:	Destination virtual address
  * @slen:	Size of the input buffer
  * @dlen:	Size of the output buffer and number of bytes produced
+ * @unit_size:  Unit size for the request for use in batching
  * @chain:	Private API code data, do not use
  * @__ctx:	Start of private context data
  */
@@ -94,6 +95,7 @@ struct acomp_req {
 	};
 	unsigned int slen;
 	unsigned int dlen;
+	unsigned int unit_size;
 
 	struct acomp_req_chain chain;
 
@@ -328,9 +330,43 @@ static inline void acomp_request_set_callback(struct acomp_req *req,
 {
 	flgs &= ~CRYPTO_ACOMP_REQ_PRIVATE;
 	flgs |= req->base.flags & CRYPTO_ACOMP_REQ_PRIVATE;
+	req->unit_size = 0;
 	crypto_request_set_callback(&req->base, flgs, cmpl, data);
 }
 
+/**
+ * acomp_request_set_unit_size() -- Sets the unit size for the request.
+ *
+ * As suggested by Herbert Xu, this is a new helper function that enables
+ * batching for zswap, IPComp, etc.
+ *
+ * Example usage model:
+ *
+ * A module like zswap that wants to use batch compression of @nr_pages with
+ * crypto_acomp must create an output SG table for the batch, initialized to
+ * contain @nr_pages SG lists. Each scatterlist is mapped to the nth
+ * destination buffer for the batch.
+ *
+ * An acomp_alg can implement batching by using the @req->unit_size to
+ * break down the SG lists passed in via @req->dst and/or @req->src, to
+ * submit individual @req->slen/@req->unit_size compress jobs or
+ * @req->dlen/@req->unit_size decompress jobs, for batch compression and
+ * batch decompression respectively.
+ *
+ * This API must be called after acomp_request_set_callback(),
+ * which sets @req->unit_size to 0.
+ *
+ * @du would be PAGE_SIZE for zswap, it could be the MTU for IPsec.
+ *
+ * @req:	asynchronous compress request
+ * @du:		data unit size of the input buffer scatterlist.
+ */
+static inline void acomp_request_set_unit_size(struct acomp_req *req,
+					       unsigned int du)
+{
+	req->unit_size = du;
+}
+
 /**
  * acomp_request_set_params() -- Sets request parameters
  *
-- 
2.27.0