uaccess.h revision 20aa7b21b1cbd1aa3fbf5fc14da5f7484a61a824 
1#ifndef __LINUX_UACCESS_H__
2#define __LINUX_UACCESS_H__
3
4#include <linux/preempt.h>
5#include <asm/uaccess.h>
6
7/*
8 * These routines enable/disable the pagefault handler in that
9 * it will not take any locks and go straight to the fixup table.
10 *
11 * They have great resemblance to the preempt_disable/enable calls
12 * and in fact they are identical; this is because currently there is
13 * no other way to make the pagefault handlers do this. So we do
14 * disable preemption but we don't necessarily care about that.
15 */
16static inline void pagefault_disable(void)
17{
18	inc_preempt_count();
19	/*
20	 * make sure to have issued the store before a pagefault
21	 * can hit.
22	 */
23	barrier();
24}
25
26static inline void pagefault_enable(void)
27{
28	/*
29	 * make sure to issue those last loads/stores before enabling
30	 * the pagefault handler again.
31	 */
32	barrier();
33	dec_preempt_count();
34	/*
35	 * make sure we do..
36	 */
37	barrier();
38	preempt_check_resched();
39}
40
41#ifndef ARCH_HAS_NOCACHE_UACCESS
42
43static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
44				const void __user *from, unsigned long n)
45{
46	return __copy_from_user_inatomic(to, from, n);
47}
48
49static inline unsigned long __copy_from_user_nocache(void *to,
50				const void __user *from, unsigned long n)
51{
52	return __copy_from_user(to, from, n);
53}
54
55#endif		/* ARCH_HAS_NOCACHE_UACCESS */
56
57/**
58 * probe_kernel_address(): safely attempt to read from a location
59 * @addr: address to read from - its type is type typeof(retval)*
60 * @retval: read into this variable
61 *
62 * Safely read from address @addr into variable @revtal.  If a kernel fault
63 * happens, handle that and return -EFAULT.
64 * We ensure that the __get_user() is executed in atomic context so that
65 * do_page_fault() doesn't attempt to take mmap_sem.  This makes
66 * probe_kernel_address() suitable for use within regions where the caller
67 * already holds mmap_sem, or other locks which nest inside mmap_sem.
68 * This must be a macro because __get_user() needs to know the types of the
69 * args.
70 *
71 * We don't include enough header files to be able to do the set_fs().  We
72 * require that the probe_kernel_address() caller will do that.
73 */
74#define probe_kernel_address(addr, retval)		\
75	({						\
76		long ret;				\
77		mm_segment_t old_fs = get_fs();		\
78							\
79		set_fs(KERNEL_DS);			\
80		pagefault_disable();			\
81		ret = __get_user(retval, addr);		\
82		pagefault_enable();			\
83		set_fs(old_fs);				\
84		ret;					\
85	})
86
87#endif		/* __LINUX_UACCESS_H__ */
88