'\" te
.\" Copyright (c) 2003, Sun Microsystems, Inc., All Rights Reserved.
.\" Copyright 1989 AT&T
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.TH STRATEGY 9E "Nov 6, 2003"
.SH NAME
strategy \- perform block I/O
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <sys/buf.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>



\fBint prefix\fR\fBstrategy\fR(\fBstruct buf *\fR\fIbp\fR);
.fi

.SH INTERFACE LEVEL
.sp
.LP
Architecture independent level 1 (DDI/DKI). This entry point is required for
block devices.
.SH PARAMETERS
.sp
.ne 2
.na
\fB\fIbp\fR \fR
.ad
.RS 7n
Pointer to the \fBbuf\fR(9S) structure.
.RE

.SH DESCRIPTION
.sp
.LP
The \fBstrategy()\fR routine is called indirectly (through \fBcb_ops\fR(9S)) by
the kernel to read and write blocks of data on the block device.
\fBstrategy()\fR may also be called directly or indirectly to support the raw
character interface of a block device (\fBread\fR(9E), \fBwrite\fR(9E) and
\fBioctl\fR(9E)). The \fBstrategy()\fR routine's responsibility is to set up
and initiate the transfer.
.sp
.LP
In general, \fBstrategy()\fR should not block. It can, however, perform a
\fBkmem_cache_create\fR(9F) with both the \fBKM_PUSHPAGE\fR and \fBKM_SLEEP\fR
flags set, which might block, without causing deadlock in low memory
situations.
.SH RETURN VALUES
.sp
.LP
The \fBstrategy()\fR function must return \fB0\fR. On an error condition, it
should call \fBbioerror\fR(9F) to set \fBb_flags\fR to the proper error code,
and call \fBbiodone\fR(9F). Note that a partial transfer is not considered to
be an error.
.SH SEE ALSO
.sp
.LP
\fBioctl\fR(9E), \fBread\fR(9E), \fBwrite\fR(9E), \fBbiodone\fR(9F),
\fBbioerror\fR(9F), \fBbuf\fR(9S), \fBcb_ops\fR(9S),
\fBkmem_cache_create\fR(9F)
.sp
.LP
\fIWriting Device Drivers\fR