__COPY_TO_USER(9) Memory Management in Linux __COPY_TO_USER(9)NAME
__copy_to_user - Copy a block of data into user space, with less checking.
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. Caller must check the specified block with access_ok before calling this function.
Returns number of bytes that could not be copied. On success, this will be zero.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 __COPY_TO_USER(9)
Check Out this Related Man Page
bcopy(9F) Kernel Functions for Drivers bcopy(9F)NAME
bcopy - copy data between address locations in the kernel
SYNOPSIS
#include <sys/types.h>
#include <sys/sunddi.h>
void bcopy(const void *from, void *to, size_t bcount);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
from Source address from which the copy is made.
to Destination address to which copy is made.
bcount The number of bytes moved.
DESCRIPTION
bcopy() copies bcount bytes from one kernel address to another. If the input and output addresses overlap, the command executes, but the
results may not be as expected.
Note that bcopy() should never be used to move data in or out of a user buffer, because it has no provision for handling page faults. The
user address space can be swapped out at any time, and bcopy() always assumes that there will be no paging faults. If bcopy() attempts to
access the user buffer when it is swapped out, the system will panic. It is safe to use bcopy() to move data within kernel space, since
kernel space is never swapped out.
CONTEXT
bcopy() can be called from user or interrupt context.
EXAMPLES
Example 1: Copying data between address locations in the kernel:
An I/O request is made for data stored in a RAM disk. If the I/O operation is a read request, the data is copied from the RAM disk to a
buffer (line 8). If it is a write request, the data is copied from a buffer to the RAM disk (line 15). bcopy() is used since both the RAM
disk and the buffer are part of the kernel address space.
1 #define RAMDNBLK 1000 /* blocks in the RAM disk */
2 #define RAMDBSIZ 512 /* bytes per block */
3 char ramdblks[RAMDNBLK][RAMDBSIZ]; /* blocks forming RAM
/* disk
...
4
5 if (bp->b_flags & B_READ) /* if read request, copy data */
6 /* from RAM disk data block */
7 /* to system buffer */
8 bcopy(&ramdblks[bp->b_blkno][0], bp->b_un.b_addr,
9 bp->b_bcount);
10
11 else /* else write request, */
12 /* copy data from a */
13 /* system buffer to RAM disk */
14 /* data block */
15 bcopy(bp->b_un.b_addr, &ramdblks[bp->b_blkno][0],
16 bp->b_bcount);
SEE ALSO copyin(9F), copyout(9F)
Writing Device Drivers
WARNINGS
The from and to addresses must be within the kernel space. No range checking is done. If an address outside of the kernel space is
selected, the driver may corrupt the system in an unpredictable way.
SunOS 5.10 4 August 2003 bcopy(9F)
hi everybody,
i am working in device drivers.As a beginner to this field ,i dont know how to read or write device files. Will copy_to_user and copy_from_user help me?
I have created a device file using mknod command .Can anybody help me in this regard :confused
thanks in advance
sriram (1 Reply)
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hi,
I need to copy strings from kernel space to user space and vice versa.
Currently if I do the following on the shell
Write from user--> kernel :echo -n abcedef > /dev/stringdrvr
read from kernel-->user :cat /dev/stringdrvr
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