BUFQ(9) 						   BSD Kernel Developer's Manual						   BUFQ(9)

NAME

     bufq, bufq_state, bufq_alloc, bufq_drain, bufq_free, bufq_getstrategyname, bufq_move, bufq_put, bufq_get, bufq_peek, bufq_cancel -- device
     buffer queues

SYNOPSIS

     #include <sys/bufq.h>

     int
     bufq_alloc(struct bufq_state **bufq, const char *strategy, int flags);

     void
     bufq_drain(struct bufq_state *bufq);

     void
     bufq_free(struct bufq_state *bufq);

     const char *
     bufq_getstrategyname(struct bufq_state *bufq);

     void
     bufq_move(struct bufq_state *dst, struct bufq_state *src);

     void
     bufq_put(struct bufq_state *bufq, struct buf *bp);

     struct buf *
     bufq_get(struct bufq_state *bufq);

     struct buf *
     bufq_peek(struct bufq_state *bufq);

     struct buf *
     bufq_cancel(struct bufq_state *bufq, struct buf *bp);

DESCRIPTION

     The bufq subsystem is a set of operations for the management of device buffer queues.

     The primary data type for using the operations is the bufq_state structure, which is opaque for users.

FUNCTIONS

     bufq_alloc(bufq, strategy, flags)
	      Allocate and initialize a bufq_state descriptor.

	      The argument strategy specifies a buffer queue strategy to be used for this buffer queue.  The following special values can be used:

		    BUFQ_STRAT_ANY	     Let bufq_alloc() select a strategy.
		    BUFQ_DISK_DEFAULT_STRAT  Let bufq_alloc() select a strategy, assuming it will be used for a normal disk device.

	      Valid bits for the flags are:

		    BUFQ_SORT_RAWBLOCK	sort by b_rawblkno
		    BUFQ_SORT_CYLINDER	sort by b_cylinder and then by b_rawblkno
		    BUFQ_EXACT		Fail if a strategy specified by strategy is not available.  In that case, bufq_alloc returns ENOENT.  If
					this flag is not specified, bufq_alloc() will silently use one of available strategies.

     bufq_drain(bufq)
	      Drain a bufq_state descriptor.

     bufq_free(bufq)
	      Destroy a bufq_state descriptor.

     bufq_getstrategyname(bufq)
	      Get a strategy identifier of a buffer queue, the string returned will be NUL-terminated and it always will be a valid strategy name.

     bufq_move(dst, src)
	      Move all requests from the buffer queue src to the buffer queue dst.

     bufq_put(bufq, bp)
	      Put the buf bp in the queue.

     bufq_get(bufq)
	      Get the next buf from the queue and remove it from the queue.  Returns NULL if the queue is empty.

     bufq_peek(bufq)
	      Get the next buf from the queue without removal.	The next buf will remain the same until bufq_get(), bufq_put(), or bufq_drain() is
	      called.  Returns NULL if the queue is empty.

     bufq_cancel(bufq, bp)
	      Cancel the buf bp issued earlier on the queue.  Returns NULL if the element can not be found on the queue or bp if it has been found
	      and removed.  This operation can be computationally expensive if there are a lot of buffers queued.

CODE REFERENCES

     The actual code implementing the device buffer queues can be found in the file sys/kern/subr_bufq.c.

HISTORY

     The bufq subsystem appeared in NetBSD 2.0.

AUTHORS

     The bufq subsystem was written by Jurgen Hannken-Illjes <hannken@NetBSD.org>.

BSD
								 January 24, 2009							       BSD