opensolaris man page for id32_free

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
       Solaris architecture specific (Solaris 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 Solaris 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 Once id32_free() is called, the supplied token is no longer valid.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
       These functions can be called from user or interrupt context. The routine id32_alloc() should not be called from interrupt context when the
       KM_SLEEP flag is passed in. All other routines can be called from interrupt or kernel context.

SEE ALSO
       kmem_alloc(9F)

       Writing Device Drivers

SunOS 5.11							    12 Dec 2001 						    id32_alloc(9F)