bcopy(9F)

NAME

     bcopy - copy data between address locations in the kernel

SYNOPSIS

     #include <sys/types.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 han-
     dling 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.