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


devmap_unload, devmap_load - control validation of memory address


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

int devmap_load(devmap_cookie_t dhp, offset_t off, size_t len,
uint_t type, uint_t rw);

int devmap_unload(devmap_cookie_t dhp, offset_t off, size_t len);


illumos DDI specific (illumos DDI).


An opaque mapping handle that the system uses to describe the

User offset within the logical device memory at which the loading
or unloading of the address translations begins.

Length (in bytes) of the range being affected.

devmap_load() only
Type of access operation.

Direction of access.


devmap_unload() and devmap_load() are used to control the validation of
the memory mapping described by dhp in the specified range.
devmap_unload() invalidates the mapping translations and will generate
calls to the devmap_access(9E) entry point next time the mapping is
accessed. The drivers use devmap_load() to validate the mapping
translations during memory access.

A typical use of devmap_unload() and devmap_load() is in the driver's
context management callback function, devmap_contextmgt(9E). To manage a
device context, a device driver calls devmap_unload() on the context
about to be switched out. It switches contexts, and then calls
devmap_load() on the context switched in. devmap_unload() can be used
to unload the mappings of other processes as well as the mappings of the
calling process, but devmap_load() can only be used to load the mappings
of the calling process. Attempting to load another process's mappings
with devmap_load() will result in a system panic.

For both routines, the range to be affected is defined by the off and len
arguments. Requests affect the entire page containing the off and all
pages up to and including the page containing the last byte as indicated
by off + len. The arguments type and rw are provided by the system to the
calling function (for example, devmap_contextmgt(9E)) and should not be

Supplying a value of 0 for the len argument affects all addresses from
the off to the end of the mapping. Supplying a value of 0 for the off
argument and a value of 0 for len argument affect all addresses in the

A non-zero return value from either devmap_unload() or devmap_load() will
cause the corresponding operation to fail. The failure may result in a
SIGSEGV or SIGBUS signal being delivered to the process.


Successful completion.

An error occurred.


These routines can be called from user or kernel context only.


Example 1: Managing a One-Page Device Context

The following shows an example of managing a device context that is one
page in length.

struct xx_context cur_ctx;

static int
xxdevmap_contextmgt(devmap_cookie_t dhp, void *pvtp, offset_t off,
size_t len, uint_t type, uint_t rw)
int err;
devmap_cookie_t cur_dhp;
struct xx_pvt *p;
struct xx_pvt *pvp = (struct xx_pvt *)pvtp;
/* enable access callbacks for the current mapping */
if (cur_ctx != NULL && cur_ctx != pvp->ctx) {
p = cur_ctx->pvt;
* unload the region from off to the end of the mapping.
cur_dhp = p->dhp;
if ((err = devmap_unload(cur_dhp, off, len)) != 0)
return (err);
/* Switch device context - device dependent*/
/* Make handle the new current mapping */
cur_ctx = pvp->ctx;
* Disable callbacks and complete the access for the
* mapping that generated this callback.
return (devmap_load(pvp->dhp, off, len, type, rw));


devmap_access(9E), devmap_contextmgt(9E)

Writing Device Drivers

January 22, 1997 DEVMAP_UNLOAD(9F)