user_dma.c

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/*
 * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
 * Portions based on net/core/datagram.c and copyrighted by their authors.
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59
 * Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * The full GNU General Public License is included in this distribution in the
 * file called COPYING.
 */

/*
 * This code allows the net stack to make use of a DMA engine for
 * skb to iovec copies.
 */

#include <linux/dmaengine.h>
#include <linux/socket.h>
#include <linux/export.h>
#include <net/tcp.h>
#include <net/netdma.h>

#define NET_DMA_DEFAULT_COPYBREAK 4096

int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_COPYBREAK;
EXPORT_SYMBOL(sysctl_tcp_dma_copybreak);

int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
            struct sk_buff *skb, int offset, struct iovec *to,
            size_t len, struct dma_pinned_list *pinned_list)
{
    int start = skb_headlen(skb);
    int i, copy = start - offset;
    struct sk_buff *frag_iter;
    dma_cookie_t cookie = 0;

    /* Copy header. */
    if (copy > 0) {
        if (copy > len)
            copy = len;
        cookie = dma_memcpy_to_iovec(chan, to, pinned_list,
                        skb->data + offset, copy);
        if (cookie < 0)
            goto fault;
        len -= copy;
        if (len == 0)
            goto end;
        offset += copy;
    }

    /* Copy paged appendix. Hmm... why does this look so complicated? */
    for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
        int end;
        const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

        WARN_ON(start > offset + len);

        end = start + skb_frag_size(frag);
        copy = end - offset;
        if (copy > 0) {
            struct page *page = skb_frag_page(frag);

            if (copy > len)
                copy = len;

            cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list, page,
                    frag->page_offset + offset - start, copy);
            if (cookie < 0)
                goto fault;
            len -= copy;
            if (len == 0)
                goto end;
            offset += copy;
        }
        start = end;
    }

    skb_walk_frags(skb, frag_iter) {
        int end;

        WARN_ON(start > offset + len);

        end = start + frag_iter->len;
        copy = end - offset;
        if (copy > 0) {
            if (copy > len)
                copy = len;
            cookie = dma_skb_copy_datagram_iovec(chan, frag_iter,
                                 offset - start,
                                 to, copy,
                                 pinned_list);
            if (cookie < 0)
                goto fault;
            len -= copy;
            if (len == 0)
                goto end;
            offset += copy;
        }
        start = end;
    }

end:
    if (!len) {
        skb->dma_cookie = cookie;
        return cookie;
    }

fault:
    return -EFAULT;
}