BUFQ(9)                NetBSD 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 struc-
     ture, 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 strat-
                                             egy.
                    BUFQ_DISK_DEFAULT_STRAT  Let bufq_alloc() select a strat-
                                             egy, 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 expen-
              sive 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 Jürgen Hannken-Illjes
     <hannken@NetBSD.org>.

NetBSD 6.1.5                   January 24, 2009                   NetBSD 6.1.5

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