bufq(9) - NetBSD Manual Pages

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 -- 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);


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.


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 Juergen Hannken-Illjes
     <hannken@NetBSD.org>.

NetBSD 4.0                     December 26, 2005                    NetBSD 4.0