[CRYPTO] scatterwalk: Prepare for block ciphers

This patch prepares the scatterwalk code for use by the new block cipher
type.

Firstly it halves the size of scatter_walk on 32-bit platforms.  This
is important as we allocate at least two of these objects on the stack
for each block cipher operation.

It also exports the symbols since the block cipher code can be built as
a module.

Finally there is a hack in scatterwalk_unmap that relies on progress
being made.  Unfortunately, for hardware crypto we can't guarantee
progress to be made since the hardware can fail.

So this also gets rid of the hack by not advancing the address returned
by scatterwalk_map.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/scatterwalk.c

@@ -15,9 +15,11 @@
  */
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/module.h>
 #include <linux/pagemap.h>
 #include <linux/highmem.h>
-#include <asm/scatterlist.h>
+#include <linux/scatterlist.h>
+
 #include "internal.h"
 #include "scatterwalk.h"
 
@@ -27,88 +29,77 @@ enum km_type crypto_km_types[] = {
 	KM_SOFTIRQ0,
 	KM_SOFTIRQ1,
 };
+EXPORT_SYMBOL_GPL(crypto_km_types);
 
-static void memcpy_dir(void *buf, void *sgdata, size_t nbytes, int out)
+static inline void memcpy_dir(void *buf, void *sgdata, size_t nbytes, int out)
 {
-	if (out)
-		memcpy(sgdata, buf, nbytes);
-	else
-		memcpy(buf, sgdata, nbytes);
+	void *src = out ? buf : sgdata;
+	void *dst = out ? sgdata : buf;
+
+	memcpy(dst, src, nbytes);
 }
 
 void scatterwalk_start(struct scatter_walk *walk, struct scatterlist *sg)
 {
-	unsigned int rest_of_page;
-
 	walk->sg = sg;
 
-	walk->page = sg->page;
-	walk->len_this_segment = sg->length;
-
 	BUG_ON(!sg->length);
 
-	rest_of_page = PAGE_CACHE_SIZE - (sg->offset & (PAGE_CACHE_SIZE - 1));
-	walk->len_this_page = min(sg->length, rest_of_page);
 	walk->offset = sg->offset;
 }
+EXPORT_SYMBOL_GPL(scatterwalk_start);
 
-void scatterwalk_map(struct scatter_walk *walk, int out)
+void *scatterwalk_map(struct scatter_walk *walk, int out)
 {
-	walk->data = crypto_kmap(walk->page, out) + walk->offset;
-}
-
-static inline void scatterwalk_unmap(struct scatter_walk *walk, int out)
-{
-	/* walk->data may be pointing the first byte of the next page;
-	   however, we know we transfered at least one byte.  So,
-	   walk->data - 1 will be a virtual address in the mapped page. */
-	crypto_kunmap(walk->data - 1, out);
+	return crypto_kmap(scatterwalk_page(walk), out) +
+	       offset_in_page(walk->offset);
 }
+EXPORT_SYMBOL_GPL(scatterwalk_map);
 
 static void scatterwalk_pagedone(struct scatter_walk *walk, int out,
 				 unsigned int more)
 {
 	if (out)
-		flush_dcache_page(walk->page);
+		flush_dcache_page(scatterwalk_page(walk));
 
 	if (more) {
-		walk->len_this_segment -= walk->len_this_page;
-
-		if (walk->len_this_segment) {
-			walk->page++;
-			walk->len_this_page = min(walk->len_this_segment,
-						  (unsigned)PAGE_CACHE_SIZE);
-			walk->offset = 0;
-		}
-		else
+		walk->offset += PAGE_SIZE - 1;
+		walk->offset &= PAGE_MASK;
+		if (walk->offset >= walk->sg->offset + walk->sg->length)
 			scatterwalk_start(walk, sg_next(walk->sg));
 	}
 }
 
 void scatterwalk_done(struct scatter_walk *walk, int out, int more)
 {
-	scatterwalk_unmap(walk, out);
-	if (walk->len_this_page == 0 || !more)
+	if (!offset_in_page(walk->offset) || !more)
 		scatterwalk_pagedone(walk, out, more);
 }
+EXPORT_SYMBOL_GPL(scatterwalk_done);
 
-/*
- * Do not call this unless the total length of all of the fragments
- * has been verified as multiple of the block size.
- */
-int scatterwalk_copychunks(void *buf, struct scatter_walk *walk,
-			   size_t nbytes, int out)
+void scatterwalk_copychunks(void *buf, struct scatter_walk *walk,
+			    size_t nbytes, int out)
 {
-	while (nbytes > walk->len_this_page) {
-		memcpy_dir(buf, walk->data, walk->len_this_page, out);
-		buf += walk->len_this_page;
-		nbytes -= walk->len_this_page;
+	for (;;) {
+		unsigned int len_this_page = scatterwalk_pagelen(walk);
+		u8 *vaddr;
+
+		if (len_this_page > nbytes)
+			len_this_page = nbytes;
+
+		vaddr = scatterwalk_map(walk, out);
+		memcpy_dir(buf, vaddr, len_this_page, out);
+		scatterwalk_unmap(vaddr, out);
+
+		if (nbytes == len_this_page)
+			break;
+
+		buf += len_this_page;
+		nbytes -= len_this_page;
 
-		scatterwalk_unmap(walk, out);
 		scatterwalk_pagedone(walk, out, 1);
-		scatterwalk_map(walk, out);
 	}
 
-	memcpy_dir(buf, walk->data, nbytes, out);
-	return nbytes;
+	scatterwalk_advance(walk, nbytes);
 }
+EXPORT_SYMBOL_GPL(scatterwalk_copychunks);