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 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⟩.
BSD January 24, 2009 BSD
