STRATEGY(9E) Driver Entry Points STRATEGY(9E)

NAME

strategy - perform block I/O

SYNOPSIS

#include <sys/types.h>
#include <sys/buf.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>


int prefixstrategy(struct buf *bp);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI). This entry point is
required for block devices.

PARAMETERS

bp
Pointer to the buf(9S) structure.

DESCRIPTION

The strategy() routine is called indirectly (through cb_ops(9S)) by
the kernel to read and write blocks of data on the block device.
strategy() may also be called directly or indirectly to support the
raw character interface of a block device (read(9E), write(9E) and
ioctl(9E)). The strategy() routine's responsibility is to set up and
initiate the transfer.


In general, strategy() should not block. It can, however, perform a
kmem_cache_create(9F) with both the KM_PUSHPAGE and KM_SLEEP flags
set, which might block, without causing deadlock in low memory
situations.

RETURN VALUES

The strategy() function must return 0. On an error condition, it
should call bioerror(9F) to set b_flags to the proper error code, and
call biodone(9F). Note that a partial transfer is not considered to
be an error.

SEE ALSO

ioctl(9E), read(9E), write(9E), biodone(9F), bioerror(9F),
kmem_cache_create(9F), buf(9S), cb_ops(9S)


Writing Device Drivers

November 6, 2003 STRATEGY(9E)