illumos: manual page: id32

ID32_ALLOC(9F) Kernel Functions for Drivers ID32_ALLOC(9F)

NAME

id32_alloc, id32_free, id32_lookup - 32-bit driver ID management routines

SYNOPSIS

#include <sys/ddi.h>
#include <sys/id32.h>

uint32_t id32_alloc(void *ptr, int flag);

void id32_free(uint32_t token);

void *id32_lookup(uint32_t token);

INTERFACE LEVEL

illumos architecture specific (illumos DDI).

PARAMETERS

ptr
any valid 32- or 64-bit pointer

flag
determines whether caller can sleep for memory (see
kmem_alloc(9F) for a description)

DESCRIPTION

These routines were originally developed so that device drivers could
manage 64-bit pointers on devices that save space only for 32-bit
pointers.

Many device drivers need to pass a 32-bit value to the hardware when
attempting I/O. Later, when that I/O completes, the only way the driver
has to identify the request that generated that I/O is via a "token".
When the I/O is initiated, the driver passes this token to the hardware.
When the I/O completes the hardware passes back this 32-bit token.

Before illumos supported 64-bit pointers, device drivers just passed a
raw 32-bit pointer to the hardware. When pointers grew to be 64 bits this
was no longer possible. The id32_*() routines were created to help
drivers translate between 64-bit pointers and a 32-bit token.

Given a 32- or 64-bit pointer, the routine id32_alloc() allocates a
32-bit token, returning 0 if KM_NOSLEEP was specified and memory could
not be allocated. The allocated token is passed back to id32_lookup() to
obtain the original 32- or 64-bit pointer.

The routine id32_free() is used to free an allocated token. Once
id32_free() is called, the supplied token is no longer valid.

Note that these routines have some degree of error checking. This is done
so that an invalid token passed to id32_lookup() will not be accepted as
valid. When id32_lookup() detects an invalid token it returns NULL.
Calling routines should check for this return value so that they do not
try to dereference a NULL pointer.

CONTEXT