Linux Kernel  3.7.1
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uaccess.c
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1 /*
2  * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License version 2 and
6  * only version 2 as published by the Free Software Foundation.
7  *
8  * This program is distributed in the hope that it will be useful,
9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11  * GNU General Public License for more details.
12  *
13  * You should have received a copy of the GNU General Public License
14  * along with this program; if not, write to the Free Software
15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
16  * 02110-1301, USA.
17  */
18 
19 /*
20  * Support for user memory access from kernel. This will
21  * probably be inlined for performance at some point, but
22  * for ease of debug, and to a lesser degree for code size,
23  * we implement here as subroutines.
24  */
25 #include <linux/types.h>
26 #include <asm/uaccess.h>
27 #include <asm/pgtable.h>
28 
29 /*
30  * For clear_user(), exploit previously defined copy_to_user function
31  * and the fact that we've got a handy zero page defined in kernel/head.S
32  *
33  * dczero here would be even faster.
34  */
35 __kernel_size_t __clear_user_hexagon(void __user *dest, unsigned long count)
36 {
37  long uncleared;
38 
39  while (count > PAGE_SIZE) {
40  uncleared = __copy_to_user_hexagon(dest, &empty_zero_page,
41  PAGE_SIZE);
42  if (uncleared)
43  return count - (PAGE_SIZE - uncleared);
44  count -= PAGE_SIZE;
45  dest += PAGE_SIZE;
46  }
47  if (count)
48  count = __copy_to_user_hexagon(dest, &empty_zero_page, count);
49 
50  return count;
51 }
52 
53 unsigned long clear_user_hexagon(void __user *dest, unsigned long count)
54 {
55  if (!access_ok(VERIFY_WRITE, dest, count))
56  return count;
57  else
58  return __clear_user_hexagon(dest, count);
59 }