root/net/core/user_dma.c

DEFINITIONS

1. dma_skb_copy_datagram_iovec

/*
 * 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 <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);

/**
 *      dma_skb_copy_datagram_iovec - Copy a datagram to an iovec.
 *      @skb - buffer to copy
 *      @offset - offset in the buffer to start copying from
 *      @iovec - io vector to copy to
 *      @len - amount of data to copy from buffer to iovec
 *      @pinned_list - locked iovec buffer data
 *
 *      Note: the iovec is modified during the copy.
 */
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;
        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;

                WARN_ON(start > offset + len);

                end = start + skb_shinfo(skb)->frags[i].size;
                copy = end - offset;
                if (copy > 0) {
                        skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
                        struct page *page = frag->page;

                        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;
        }

        if (skb_shinfo(skb)->frag_list) {
                struct sk_buff *list = skb_shinfo(skb)->frag_list;

                for (; list; list = list->next) {
                        int end;

                        WARN_ON(start > offset + len);

                        end = start + list->len;
                        copy = end - offset;
                        if (copy > 0) {
                                if (copy > len)
                                        copy = len;
                                cookie = dma_skb_copy_datagram_iovec(chan, list,
                                                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;
}