1. 根目录:
2. crypto
3. scatterwalk.c

/*
 * Cryptographic API.
 *
 * Cipher operations.
 *
 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
 *               2002 Adam J. Richter <adam@yggdrasil.com>
 *               2004 Jean-Luc Cooke <jlcooke@certainkey.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 */

#include <crypto/scatterwalk.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/scatterlist.h>

static inline void memcpy_dir(void *buf, void *sgdata, size_t nbytes, int out)
{
	void *src = out ? buf : sgdata;
	void *dst = out ? sgdata : buf;

	memcpy(dst, src, nbytes);
}

void scatterwalk_start(struct scatter_walk *walk, struct scatterlist *sg)
{
	walk->sg = sg;

	BUG_ON(!sg->length);

	walk->offset = sg->offset;
}
EXPORT_SYMBOL_GPL(scatterwalk_start);

void *scatterwalk_map(struct scatter_walk *walk)
{
	return kmap_atomic(scatterwalk_page(walk)) +
	       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) {
		struct page *page;

		page = sg_page(walk->sg) + ((walk->offset - 1) >> PAGE_SHIFT);
		/* Test ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE first as
		 * PageSlab cannot be optimised away per se due to
		 * use of volatile pointer.
		 */
		if (ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE && !PageSlab(page))
			flush_dcache_page(page);
	}

	if (more) {
		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)
{
	if (!(scatterwalk_pagelen(walk) & (PAGE_SIZE - 1)) || !more)
		scatterwalk_pagedone(walk, out, more);
}
EXPORT_SYMBOL_GPL(scatterwalk_done);

void scatterwalk_copychunks(void *buf, struct scatter_walk *walk,
			    size_t nbytes, int out)
{
	for (;;) {
		unsigned int len_this_page = scatterwalk_pagelen(walk);
		u8 *vaddr;

		if (len_this_page > nbytes)
			len_this_page = nbytes;

		vaddr = scatterwalk_map(walk);
		memcpy_dir(buf, vaddr, len_this_page, out);
		scatterwalk_unmap(vaddr);

		scatterwalk_advance(walk, len_this_page);

		if (nbytes == len_this_page)
			break;

		buf += len_this_page;
		nbytes -= len_this_page;

		scatterwalk_pagedone(walk, out, 1);
	}
}
EXPORT_SYMBOL_GPL(scatterwalk_copychunks);

void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
			      unsigned int start, unsigned int nbytes, int out)
{
	struct scatter_walk walk;
	struct scatterlist tmp[2];

	if (!nbytes)
		return;

	sg = scatterwalk_ffwd(tmp, sg, start);

	if (sg_page(sg) == virt_to_page(buf) &&
	    sg->offset == offset_in_page(buf))
		return;

	scatterwalk_start(&walk, sg);
	scatterwalk_copychunks(buf, &walk, nbytes, out);
	scatterwalk_done(&walk, out, 0);
}
EXPORT_SYMBOL_GPL(scatterwalk_map_and_copy);

int scatterwalk_bytes_sglen(struct scatterlist *sg, int num_bytes)
{
	int offset = 0, n = 0;

	/* num_bytes is too small */
	if (num_bytes < sg->length)
		return -1;

	do {
		offset += sg->length;
		n++;
		sg = sg_next(sg);

		/* num_bytes is too large */
		if (unlikely(!sg && (num_bytes < offset)))
			return -1;
	} while (sg && (num_bytes > offset));

	return n;
}
EXPORT_SYMBOL_GPL(scatterwalk_bytes_sglen);

struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
				     struct scatterlist *src,
				     unsigned int len)
{
	for (;;) {
		if (!len)
			return src;

		if (src->length > len)
			break;

		len -= src->length;
		src = sg_next(src);
	}

	sg_init_table(dst, 2);
	sg_set_page(dst, sg_page(src), src->length - len, src->offset + len);
	scatterwalk_crypto_chain(dst, sg_next(src), 0, 2);

	return dst;
}
EXPORT_SYMBOL_GPL(scatterwalk_ffwd);