linux/net/core/user_dma.c
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   1/*
   2 * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
   3 * Portions based on net/core/datagram.c and copyrighted by their authors.
   4 *
   5 * This program is free software; you can redistribute it and/or modify it
   6 * under the terms of the GNU General Public License as published by the Free
   7 * Software Foundation; either version 2 of the License, or (at your option)
   8 * any later version.
   9 *
  10 * This program is distributed in the hope that it will be useful, but WITHOUT
  11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13 * more details.
  14 *
  15 * You should have received a copy of the GNU General Public License along with
  16 * this program; if not, write to the Free Software Foundation, Inc., 59
  17 * Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  18 *
  19 * The full GNU General Public License is included in this distribution in the
  20 * file called COPYING.
  21 */
  22
  23/*
  24 * This code allows the net stack to make use of a DMA engine for
  25 * skb to iovec copies.
  26 */
  27
  28#include <linux/dmaengine.h>
  29#include <linux/socket.h>
  30#include <linux/export.h>
  31#include <net/tcp.h>
  32#include <net/netdma.h>
  33
  34#define NET_DMA_DEFAULT_COPYBREAK 4096
  35
  36int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_COPYBREAK;
  37EXPORT_SYMBOL(sysctl_tcp_dma_copybreak);
  38
  39/**
  40 *      dma_skb_copy_datagram_iovec - Copy a datagram to an iovec.
  41 *      @skb - buffer to copy
  42 *      @offset - offset in the buffer to start copying from
  43 *      @iovec - io vector to copy to
  44 *      @len - amount of data to copy from buffer to iovec
  45 *      @pinned_list - locked iovec buffer data
  46 *
  47 *      Note: the iovec is modified during the copy.
  48 */
  49int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
  50                        struct sk_buff *skb, int offset, struct iovec *to,
  51                        size_t len, struct dma_pinned_list *pinned_list)
  52{
  53        int start = skb_headlen(skb);
  54        int i, copy = start - offset;
  55        struct sk_buff *frag_iter;
  56        dma_cookie_t cookie = 0;
  57
  58        /* Copy header. */
  59        if (copy > 0) {
  60                if (copy > len)
  61                        copy = len;
  62                cookie = dma_memcpy_to_iovec(chan, to, pinned_list,
  63                                            skb->data + offset, copy);
  64                if (cookie < 0)
  65                        goto fault;
  66                len -= copy;
  67                if (len == 0)
  68                        goto end;
  69                offset += copy;
  70        }
  71
  72        /* Copy paged appendix. Hmm... why does this look so complicated? */
  73        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  74                int end;
  75                const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  76
  77                WARN_ON(start > offset + len);
  78
  79                end = start + skb_frag_size(frag);
  80                copy = end - offset;
  81                if (copy > 0) {
  82                        struct page *page = skb_frag_page(frag);
  83
  84                        if (copy > len)
  85                                copy = len;
  86
  87                        cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list, page,
  88                                        frag->page_offset + offset - start, copy);
  89                        if (cookie < 0)
  90                                goto fault;
  91                        len -= copy;
  92                        if (len == 0)
  93                                goto end;
  94                        offset += copy;
  95                }
  96                start = end;
  97        }
  98
  99        skb_walk_frags(skb, frag_iter) {
 100                int end;
 101
 102                WARN_ON(start > offset + len);
 103
 104                end = start + frag_iter->len;
 105                copy = end - offset;
 106                if (copy > 0) {
 107                        if (copy > len)
 108                                copy = len;
 109                        cookie = dma_skb_copy_datagram_iovec(chan, frag_iter,
 110                                                             offset - start,
 111                                                             to, copy,
 112                                                             pinned_list);
 113                        if (cookie < 0)
 114                                goto fault;
 115                        len -= copy;
 116                        if (len == 0)
 117                                goto end;
 118                        offset += copy;
 119                }
 120                start = end;
 121        }
 122
 123end:
 124        if (!len) {
 125                skb->dma_cookie = cookie;
 126                return cookie;
 127        }
 128
 129fault:
 130        return -EFAULT;
 131}
 132
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