scatterwalk.c

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/*
 * Cryptographic API.
 *
 * Cipher operations.
 *
 * Copyright (c) 2002 James Morris <[email protected]>
 *               2002 Adam J. Richter <[email protected]>
 *               2004 Jean-Luc Cooke <[email protected]>
 *
 * 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 <linux/kernel.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <asm/scatterlist.h>
#include "internal.h"
#include "scatterwalk.h"

void *scatterwalk_whichbuf(struct scatter_walk *walk, unsigned int nbytes, void *scratch)
{
    if (nbytes <= walk->len_this_page &&
        (((unsigned long)walk->data) & (PAGE_CACHE_SIZE - 1)) + nbytes <=
        PAGE_CACHE_SIZE)
        return walk->data;
    else
        return scratch;
}

static void memcpy_dir(void *buf, void *sgdata, size_t nbytes, int out)
{
    if (out)
        memcpy(sgdata, buf, nbytes);
    else
        memcpy(buf, sgdata, 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;

    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;
}

void scatterwalk_map(struct scatter_walk *walk)
{
    walk->data = kmap_atomic(walk->page) + walk->offset;
}

static void scatterwalk_pagedone(struct scatter_walk *walk, int out,
                 unsigned int more)
{
    /* walk->data may be pointing the first byte of the next page;
       however, we know we transferred at least one byte.  So,
       walk->data - 1 will be a virtual address in the mapped page. */

    if (out)
        flush_dcache_page(walk->page);

    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
            scatterwalk_start(walk, sg_next(walk->sg));
    }
}

void scatterwalk_done(struct scatter_walk *walk, int out, int more)
{
    crypto_kunmap(walk->data, out);
    if (walk->len_this_page == 0 || !more)
        scatterwalk_pagedone(walk, out, more);
}

/*
 * 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)
{
    if (buf != walk->data) {
        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;

            kunmap_atomic(walk->data);
            scatterwalk_pagedone(walk, out, 1);
            scatterwalk_map(walk);
        }

        memcpy_dir(buf, walk->data, nbytes, out);
    }

    walk->offset += nbytes;
    walk->len_this_page -= nbytes;
    walk->len_this_segment -= nbytes;
    return 0;
}