Writing Device Drivers

devmap_access() Entry Point

The devmap_access(9E) entry point is called when an access is made to a mapping whose translations are invalid. Mapping translations are invalidated when the mapping is created with devmap_devmem_setup(9F) in response to mmap(2), duplicated by fork(2), or explicitly invalidated by a call to devmap_unload(9F).

The syntax for devmap_access() is as follows:

int xxdevmap_access(devmap_cookie_t handle, void *devprivate,
    offset_t offset, size_t len, uint_t type, uint_t rw);



Mapping handle of the mapping that was accessed by a user process.


Pointer to the driver private data associated with the mapping.


Offset within the mapping that was accessed.


Length in bytes of the memory being accessed.


Type of access operation.


Specifies the direction of access.

The system expects devmap_access(9E) to call either devmap_do_ctxmgt(9F) or devmap_default_access(9F) to load the memory address translations before devmap_access() returns. For mappings that support context switching, the device driver should call devmap_do_ctxmgt(). This routine is passed all parameters from devmap_access(9E), as well as a pointer to the driver entry point devmap_contextmgt(9E), which handles the context switching. For mappings that do not support context switching, the driver should call devmap_default_access(9F). The purpose of devmap_default_access() is to call devmap_load(9F) to load the user translation.

The following example shows a devmap_access(9E) entry point. The mapping is divided into two regions. The region that starts at offset OFF_CTXMG with a length of CTXMGT_SIZE bytes supports context management. The rest of the mapping supports default access.

Example 11–2 Using the devmap_access() Routine

#define OFF_CTXMG      0
#define CTXMGT_SIZE    0x20000    
static int
xxdevmap_access(devmap_cookie_t handle, void *devprivate,
    offset_t off, size_t len, uint_t type, uint_t rw)
    offset_t diff;
    int    error;

    if ((diff = off - OFF_CTXMG) >= 0 && diff < CTXMGT_SIZE) {
        error = devmap_do_ctxmgt(handle, devprivate, off,
            len, type, rw, xxdevmap_contextmgt);
    } else {
        error = devmap_default_access(handle, devprivate,
            off, len, type, rw);
    return (error);