BUFQ_INIT(9) BSD Kernel Developer's Manual BUFQ_INIT(9)
bufq_init, bufq_switch, bufq_destroy, bufq_queue, bufq_dequeue,
bufq_requeue, bufq_peek, bufq_drain -- buf queues
bufq_init(struct bufq *bufq, int type);
bufq_switch(struct bufq *bufq, int type);
bufq_destroy(struct bufq *bufq);
bufq_queue(struct bufq *bufq, struct buf *bp);
struct buf *
bufq_dequeue(struct bufq *bufq);
bufq_requeue(struct bufq *bufq, struct buf *bp);
bufq_peek(struct bufq *bufq);
bufq_drain(struct bufq *bufq);
The bufq API implements queueing and scheduling of I/O operations on disk
devices. It provides multiple scheduling algorithms within the API.
It is the responsibility of the disk device driver to provide pre-allo-
cated bufq structures.
bufq_init() initialiases the bufq structure and allocates any state
required by the scheduling algorithm by the type argument.
bufq_switch() can be used to change the scheduler currently used by bufq
to the algorithm specified by type.
The type argument to bufq_init() and bufq_switch() can be one of the fol-
lowing scheduling algorithms:
BUFQ_FIFO A simple First-In First-Out queue.
BUFQ_NSCAN Takes batches of "N" bufs from the queue and sorts
them for optimal head movement.
BUFQ_DEFAULT This currently aliases BUFQ_NSCAN.
bufq_destroy() frees any state that was used by the scheduler.
bufq_queue() is used to add the buf specified by bp to the bufq queue.
bufq_dequeue() is used to get the next buf the bufq has scheduled to be
serviced by a disk. The buf will be removed from the queue.
bufq_requeue() can be used to return a previously dequeued buf specified
by bp to the head of the queue of bufq.
bufq_peek() allows the caller to determine if there are more bufs queued
on bufq without modifying the list of bufs.
bufq_drain() is a convenience function for devices that have detached.
It removes all the bufs currently queued on bufq, marks them as failed
with an ENXIO error, and returns them to the block layer via biodone(9).
bufq_init(), bufq_switch(), and bufq_destroy() can be called during auto-
conf, or from process context.
bufq_queue, bufq_dequeue, bufq_requeue, bufq_peek, and bufq_drain can be
called during autoconf, from process context, or from interrupt context.
bufq_init() and bufq_switch() will return 0 on success, or an error code
as per errno(2).
bufq_dequeue() returns the next buf that is scheduled to be serviced by
the disk. NULL is returned if there are no bufs available on the queue.
bufq_peek() returns 1 if there are bufs available to be scheduled on the
disk, otherwise 0.
errno(2), autoconf(9), biodone(9), disk(9)
The bufq API was written by Thordur I. Bjornsson and David Gwynne
<email@example.com>. The bufq API first appeared in OpenBSD 4.8 and
finally succeeded in fully replacing disksort in OpenBSD 5.5.
BSD August 8, 2014 BSD