bufq(9) [netbsd man page]

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

Check Out this Related Man Page

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)

Linux and UNIX Man Pages

bufq(9) [netbsd man page]

Check Out this Related Man Page