Content-type: text/html Man page of segmap


Section: Driver Entry Points (9E)
Updated: 14 Jan 1997
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segmap - map device memory into user space  


#include <sys/types.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/vm.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>

int prefixsegmap(dev_t dev, off_t off, struct as *asp, caddr_t *addrp, off_t len, unsigned int prot, unsigned int maxprot, unsigned int flags, cred_t *cred_p);  


Architecture independent level 2 (DKI only).  


dev Device whose memory is to be mapped.

off Offset within device memory at which mapping begins.

asp Pointer to the address space into which the device memory should be mapped.

addrp Pointer to the address in the address space to which the device memory should be mapped.

len Length (in bytes) of the memory to be mapped.

prot A bit field that specifies the protections. Possible settings are:

"small and bold">PROT_READ Read access is desired.

PROT_WRITE Write access is desired.

PROT_EXEC Execute access is desired.

PROT_USER User-level access is desired (the mapping is being done as a result of a mmap(2) system call).

PROT_ALL All access is desired.

maxprot Maximum protection flag possible for attempted mapping; the PROT_WRITE bit may be masked out if the user opened the special file read-only.

flags Flags indicating type of mapping. Possible values are (other bits may be set):

MAP_SHARED Changes should be shared.

MAP_PRIVATE Changes are private.

cred_p Pointer to the user credentials structure.



The segmap() entry point is an optional routine for character drivers that support memory mapping. The mmap(2) system call, when applied to a character special file, allows device memory to be mapped into user space for direct access by the user application.

Typically, a character driver that needs to support the mmap(2) system call supplies either an devmap(9E) entry point, or both an devmap(9E) and a segmap() entry point routine (see the devmap(9E) reference page). If no segmap() entry point is provided for the driver, devmap_setup(9F) is used as a default.

A driver for a memory-mapped device would provide a segmap() entry point if it:

• needs to maintain a separate context for each user mapping. See devmap_setup(9F) for details.

• needs to assign device access attributes to the user mapping.

The responsibilities of a segmap() entry point are:

• Verify that the range, defined by offset and len, to be mapped is valid for the device. Typically, this task is performed by calling the devmap(9E) entry point. Note that if you are using ddi_devmap_segmap(9F) or devmap_setup(9F) to set up the mapping, it will call your devmap(9E) entry point for you to validate the range to be mapped.

• Assign device access attributes to the mapping. See ddi_devmap_segmap(9F), and ddi_device_acc_attr(9S) for details.

• Set up device contexts for the user mapping if your device requires context switching. See devmap_setup(9F) for details.

• Perform the mapping with ddi_devmap_segmap(9F), or devmap_setup(9F) and return the status if it fails.



The segmap() routine should return 0 if the driver is successful in performing the memory map of its device address space into the specified address space.

The segmap() must return an error number on failure. For example, valid error numbers would be ENXIO if the offset/length pair specified exceeds the limits of the device memory, or EINVAL if the driver detects an invalid type of mapping attempted.

If one of the mapping routines ddi_devmap_segmap() or devmap_setup()fails, you must return the error number returned by the respective routine.  


mmap(2), devmap(9E), devmap_setup(9F), ddi_devmap_segmap(9F), ddi_device_acc_attr(9S)

Writing Device Drivers




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Time: 02:39:35 GMT, October 02, 2010