man pages section 9: DDI and DKI Kernel Functions

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Updated: July 2014



copyout - copy data from a driver to a user program


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

int copyout(const void *driverbuf, void *userbuf, size_t cn);

Interface Level

This interface is obsolete. ddi_copyout(9F) should be used instead.



Source address in the driver from which the data is transferred.


Destination address in the user program to which the data is transferred.


Number of bytes moved.


copyout() copies data from driver buffers to user data space.

Addresses that are word-aligned are moved most efficiently. However, the driver developer is not obligated to ensure alignment. This function automatically finds the most efficient move algorithm according to address alignment.

Return Values

Under normal conditions, a 0 is returned to indicate a successful copy. Otherwise, a −1 is returned if one of the following occurs:

  • Paging fault; the driver tried to access a page of memory for which it did not have read or write access.

  • Invalid user address, such as a user area or stack area.

  • Invalid address that would have resulted in data being copied into the user block.

  • Hardware fault; a hardware error prevented access to the specified user memory. For example, an uncorrectable parity or ECC error occurred.

If a −1 is returned to the caller, driver entry point routines should return EFAULT.


copyout() can be called from user context only.


Example 1 An ioctl() Routine

A driver ioctl(9E) routine (line 10) can be used to get or set device attributes or registers. In the XX_GETREGS condition (line 17), the driver copies the current device register values to a user data area (line 18). If the specified argument contains an invalid address, an error code is returned.

 1  struct device  {      /* layout of physical device registers  */
 2       int      control;     /* physical device control word  */
 3       int      status;      /* physical device status word   */
 4       short    recv_char;   /* receive character from device */
 5       short    xmit_char;   /* transmit character to device  */
 6  };
 8  extern struct device xx_addr[]; /* phys. device regs. location */
 9    . . .
10  xx_ioctl(dev_t dev, int cmd, int arg, int mode,
11      cred_t *cred_p, int *rval_p)
12               ...
13  {
14      register struct device *rp = &xx_addr[getminor(dev) >> 4];
15      switch (cmd) {
17      case XX_GETREGS:     /* copy device regs. to user program */
18            if (copyout(rp, arg, sizeof(struct device)))
19                return(EFAULT);
20            break;
21               ...
22      }
23               ...
24  }


See attributes(5) for a description of the following attributes:

Stability Level

See also

attributes(5), ioctl(9E) , bcopy(9F), copyin(9F), ddi_copyin(9F), ddi_copyout(9F), uiomove(9F)

Writing Device Drivers for Oracle Solaris 11.2


Driver writers who intend to support layered ioctls in their ioctl(9E) routines should use ddi_copyout(9F) instead.

Driver defined locks should not be held across calls to this function.

copyout() should not be used from a streams driver. See M_COPYIN and M_COPYOUT in STREAMS Programming Guide .