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)