net/core/user_dma.c

   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/rtnetlink.h> /* for BUG_TRAP */
  31 #include <net/tcp.h>
  32
  33 #define NET_DMA_DEFAULT_COPYBREAK 4096
  34
  35 int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_COPYBREAK;
  36
  37 /**
  38  *      dma_skb_copy_datagram_iovec - Copy a datagram to an iovec.
  39  *      @skb - buffer to copy
  40  *      @offset - offset in the buffer to start copying from
  41  *      @iovec - io vector to copy to
  42  *      @len - amount of data to copy from buffer to iovec
  43  *      @pinned_list - locked iovec buffer data
  44  *
  45  *      Note: the iovec is modified during the copy.
  46  */
  47 int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
  48                         struct sk_buff *skb, int offset, struct iovec *to,
  49                         size_t len, struct dma_pinned_list *pinned_list)
  50 {
  51         int start = skb_headlen(skb);
  52         int i, copy = start - offset;
  53         dma_cookie_t cookie = 0;
  54
  55         /* Copy header. */
  56         if (copy > 0) {
  57                 if (copy > len)
  58                         copy = len;
  59                 cookie = dma_memcpy_to_iovec(chan, to, pinned_list,
  60                                             skb->data + offset, copy);
  61                 if (cookie < 0)
  62                         goto fault;
  63                 len -= copy;
  64                 if (len == 0)
  65                         goto end;
  66                 offset += copy;
  67         }
  68
  69         /* Copy paged appendix. Hmm... why does this look so complicated? */
  70         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  71                 int end;
  72
  73                 BUG_TRAP(start <= offset + len);
  74
  75                 end = start + skb_shinfo(skb)->frags[i].size;
  76                 copy = end - offset;
  77                 if ((copy = end - offset) > 0) {
  78                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  79                         struct page *page = frag->page;
  80
  81                         if (copy > len)
  82                                 copy = len;
  83
  84                         cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list, page,
  85                                         frag->page_offset + offset - start, copy);
  86                         if (cookie < 0)
  87                                 goto fault;
  88                         len -= copy;
  89                         if (len == 0)
  90                                 goto end;
  91                         offset += copy;
  92                 }
  93                 start = end;
  94         }
  95
  96         if (skb_shinfo(skb)->frag_list) {
  97                 struct sk_buff *list = skb_shinfo(skb)->frag_list;
  98
  99                 for (; list; list = list->next) {
 100                         int end;
 101
 102                         BUG_TRAP(start <= offset + len);
 103
 104                         end = start + list->len;
 105                         copy = end - offset;
 106                         if (copy > 0) {
 107                                 if (copy > len)
 108                                         copy = len;
 109                                 cookie = dma_skb_copy_datagram_iovec(chan, list,
 110                                                 offset - start, to, copy,
 111                                                 pinned_list);
 112                                 if (cookie < 0)
 113                                         goto fault;
 114                                 len -= copy;
 115                                 if (len == 0)
 116                                         goto end;
 117                                 offset += copy;
 118                         }
 119                         start = end;
 120                 }
 121         }
 122
 123 end:
 124         if (!len) {
 125                 skb->dma_cookie = cookie;
 126                 return cookie;
 127         }
 128
 129 fault:
 130         return -EFAULT;
 131 }