在从事Linux Kernel开发的过程中，user_app和kernel之间传递数据时不能使用memcpy()函数，必须使用copy_to/from_kernel或者是put/get_user。原因是kernel和user_app内存不能直接互访。
1. put_user
Name
put_user -- Write a simple value into user space.
Arguments
- x
-
Value to copy to user space.
- ptr
-
Destination address, in user space.
Context
User context only. This function may sleep.
Description
This macro copies a single simple value from kernel space to user space. It supports simple types like char and int, but not larger data types like structures or arrays.
ptr must have pointer-to-simple-variable type, and x must be assignable to the result of dereferencing ptr .
Returns zero on success, or -EFAULT on error.
2. get_user
Name
get_user -- Get a simple variable from user space.
Arguments
- x
-
Variable to store result.
- ptr
-
Source address, in user space.
Context
User context only. This function may sleep.
Description
This macro copies a single simple variable from user space to kernel space. It supports simple types like char and int, but not larger data types like structures or arrays.
ptr must have pointer-to-simple-variable type, and the result of dereferencing ptr must be assignable to x without a cast.
Returns zero on success, or -EFAULT on error. On error, the variable x is set to zero.
1. copy_to_user
Name
copy_to_user -- Copy a block of data into user space.
Synopsis
unsigned long copy_to_user (void __user * to, const void * from, unsigned long n);
Arguments
- to
-
Destination address, in user space.
- from
-
Source address, in kernel space.
- n
-
Number of bytes to copy.
Context
User context only. This function may sleep.
Description
Copy data from kernel space to user space.
Returns number of bytes that could not be copied. On success, this will be zero.
2. copy_from_user
Name
copy_from_user -- Copy a block of data from user space.
Synopsis
unsigned long copy_from_user (void * to, const void __user * from, unsigned long n);
Arguments
- to
-
Destination address, in kernel space.
- from
-
Source address, in user space.
- n
-
Number of bytes to copy.
Context
User context only. This function may sleep.
Description
Copy data from user space to kernel space.
Returns number of bytes that could not be copied. On success, this will be zero.
If some data could not be copied, this function will pad the copied data to the requested size using zero bytes.
