BCOPY(9F) Kernel Functions for Drivers BCOPY(9F)


bcopy - copy data between address locations in the kernel


#include <sys/types.h>
#include <sys/sunddi.h>

void bcopy(const void *from, void *to, size_t bcount);


Architecture independent level 1 (DDI/DKI).


Source address from which the copy is made.

Destination address to which copy is made.

The number of bytes moved.


The bcopy() function 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.


The bcopy() function can be called from user, interrupt, or kernel


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
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);
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);


copyin(9F), copyout(9F)

Writing Device Drivers


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.

illumos January 16, 2006 BCOPY(9F)