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NetBSD 6.1.5 - man page for bufq (netbsd section 9)

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 avail-
					able.  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-termi-
	      nated 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


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