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 #include <net/netdma.h>
  33
  34 #define NET_DMA_DEFAULT_COPYBREAK 4096
  35
  36 int sysctl_tcp_dma_copybreak = NET_DMA_DEFAULT_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  */
  48 int 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                 BUG_TRAP(start <= offset + len);
  75
  76                 end = start + skb_shinfo(skb)->frags[i].size;
  77                 copy = end - offset;
  78                 if ((copy = end - offset) > 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                         BUG_TRAP(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
 124 end:
 125         if (!len) {
 126                 skb->dma_cookie = cookie;
 127                 return cookie;
 128         }
 129
 130 fault:
 131         return -EFAULT;
 132 }