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

NAME

       disksort - single direction elevator seek sort for buffers

SYNOPSIS

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

       disksort(struct diskhd *dp, struct buf *bp);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI).

PARAMETERS

       dp    A	pointer  to  a diskhd structure. A diskhd structure is essentially identical to head of a buffer structure (see buf(9S)). The only
	     defined items of interest for this structure are the av_forw and av_back structure elements which are used to maintain the front  and
	     tail pointers of the forward linked I/O request queue.

       bp    A	pointer  to  a	buffer	structure.  Typically this is the I/O request that the driver receives in its strategy routine (see strat-
	     egy(9E)). The driver is responsible for initializing the b_resid structure element to a meaningful sort key value	prior  to  calling
	     disksort().

DESCRIPTION

       The function disksort() sorts a pointer to a buffer into a single forward linked list headed by the av_forw element of the argument *dp.

       It  uses a one-way elevator algorithm that sorts buffers into the queue in ascending order based upon a key value held in the argument buf-
       fer structure element b_resid.

       This value can either be the driver calculated cylinder number for the I/O request described by the buffer argument, or simply the absolute
       logical	block  for  the  I/O  request, depending on how fine grained the sort is desired to be or how applicable either quantity is to the
       device in question.

       The head of the linked list is found by use of the av_forw structure element of the argument *dp. The tail of the linked list is  found	by
       use  of	the  av_back  structure element of the argument *dp. The av_forw element of the *bp argument is used by disksort() to maintain the
       forward linkage. The value at the head of the list presumably indicates the currently active disk area.

CONTEXT

       This function can be called from user, interrupt, or kernel context.

SEE ALSO

       strategy(9E), buf(9S)

       Writing Device Drivers

WARNINGS

       The disksort() function does no locking. Therefore, any locking is completely the responsibility of the caller.

SunOS 5.11							    16 Jan 2006 						      disksort(9F)