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

disksort - single direction elevator seek sort for buffers

#include <sys/conf.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
disksort(struct diskhd *dp, struct buf *bp);

illumos DDI specific (illumos DDI).

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.


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

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 buffer 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.

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

strategy(9E), buf(9S)

Writing Device Drivers

The disksort() function does no locking. Therefore, any locking is completely the responsibility of the caller.
January 16, 2006 OmniOS