用戶空間和內核空間傳遞數據：get_user；put_user;copy_to_user;copy_from_user

在從事Linux Kernel開發的過程中，user_app和kernel之間傳遞數據時不能使用memcpy()函數，必須使用copy_to/from_kernel或者是put/get_user。原因是kernel和user_app內存不能直接互訪。

1. put_user

Name

put_user --    Write a simple value into user space.

Synopsis

put_user ( x, ptr);

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.

Synopsis

get_user ( x, ptr);

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.