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 <net/tcp.h>
  31#include <net/netdma.h>
  32
  33#define NET_DMA_DEFAULT_COPYBREAK 4096
  34
  35int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_COPYBREAK;
  36EXPORT_SYMBOL(sysctl_tcp_dma_copybreak);
  37
  38/**
  39 *      dma_skb_copy_datagram_iovec - Copy a datagram to an iovec.
  40 *      @skb - buffer to copy
  41 *      @offset - offset in the buffer to start copying from
  42 *      @iovec - io vector to copy to
  43 *      @len - amount of data to copy from buffer to iovec
  44 *      @pinned_list - locked iovec buffer data
  45 *
  46 *      Note: the iovec is modified during the copy.
  47 */
  48int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
  49                        struct sk_buff *skb, int offset, struct iovec *to,
  50                        size_t len, struct dma_pinned_list *pinned_list)
  51{
  52        int start = skb_headlen(skb);
  53        int i, copy = start - offset;
  54        dma_cookie_t cookie = 0;
  55
  56        /* Copy header. */
  57        if (copy > 0) {
  58                if (copy > len)
  59                        copy = len;
  60                cookie = dma_memcpy_to_iovec(chan, to, pinned_list,
  61                                            skb->data + offset, copy);
  62                if (cookie < 0)
  63                        goto fault;
  64                len -= copy;
  65                if (len == 0)
  66                        goto end;
  67                offset += copy;
  68        }
  69
  70        /* Copy paged appendix. Hmm... why does this look so complicated? */
  71        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  72                int end;
  73
  74                WARN_ON(start > offset + len);
  75
  76                end = start + skb_shinfo(skb)->frags[i].size;
  77                copy = end - offset;
  78                if (copy > 0) {
  79                        skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  80                        struct page *page = frag->page;
  81
  82                        if (copy > len)
  83                                copy = len;
  84
  85                        cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list, page,
  86                                        frag->page_offset + offset - start, copy);
  87                        if (cookie < 0)
  88                                goto fault;
  89                        len -= copy;
  90                        if (len == 0)
  91                                goto end;
  92                        offset += copy;
  93                }
  94                start = end;
  95        }
  96
  97        if (skb_shinfo(skb)->frag_list) {
  98                struct sk_buff *list = skb_shinfo(skb)->frag_list;
  99
 100                for (; list; list = list->next) {
 101                        int end;
 102
 103                        WARN_ON(start > offset + len);
 104
 105                        end = start + list->len;
 106                        copy = end - offset;
 107                        if (copy > 0) {
 108                                if (copy > len)
 109                                        copy = len;
 110                                cookie = dma_skb_copy_datagram_iovec(chan, list,
 111                                                offset - start, 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        }
 123
 124end:
 125        if (!len) {
 126                skb->dma_cookie = cookie;
 127                return cookie;
 128        }
 129
 130fault:
 131        return -EFAULT;
 132}
 133