Linux Kernel  3.7.1
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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 
38 
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 
123 end:
124  if (!len) {
125  skb->dma_cookie = cookie;
126  return cookie;
127  }
128 
129 fault:
130  return -EFAULT;
131 }