'\" te
.\" Copyright (c) 2009 Sun Microsystems, Inc.  All Rights Reserved.
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
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.TH BIOCLONE 9F "Jan 16, 2006"
.SH NAME
bioclone \- clone another buffer
.SH SYNOPSIS
.nf
#include <sys/ddi.h>
#include <sys/sunddi.h>

\fBstruct buf *\fR\fBbioclone\fR(\fBstruct buf\fR \fI*bp\fR, \fBoff_t\fR \fIoff\fR, \fBsize_t\fR \fIlen\fR, \fBdev_t\fR \fIdev\fR,
     \fBdaddr_t\fR \fIblkno\fR, \fBint (\fR\fI*iodone\fR) (struct buf \fI*\fR), \fBstruct buf\fR \fI*bp_mem\fR,
     \fBint\fR \fIsleepflag\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI).
.SH PARAMETERS
.ne 2
.na
\fB\fIbp\fR\fR
.ad
.RS 13n
Pointer to the \fBbuf\fR(9S) structure describing the original \fBI/O\fR
request.
.RE

.sp
.ne 2
.na
\fB\fIoff\fR\fR
.ad
.RS 13n
Offset within original \fBI/O\fR request where new \fBI/O\fR request should
start.
.RE

.sp
.ne 2
.na
\fB\fIlen\fR\fR
.ad
.RS 13n
Length of the \fBI/O \fRrequest.
.RE

.sp
.ne 2
.na
\fB\fIdev\fR\fR
.ad
.RS 13n
Device number.
.RE

.sp
.ne 2
.na
\fB\fIblkno\fR\fR
.ad
.RS 13n
Block number on device.
.RE

.sp
.ne 2
.na
\fB\fIiodone\fR\fR
.ad
.RS 13n
Specific \fBbiodone\fR(9F) routine.
.RE

.sp
.ne 2
.na
\fB\fIbp_mem\fR\fR
.ad
.RS 13n
Pointer to a buffer structure to be filled in or \fBNULL. \fR
.RE

.sp
.ne 2
.na
\fB\fIsleepflag\fR\fR
.ad
.RS 13n
Determines whether caller can sleep for memory. Possible flags are
\fBKM_SLEEP\fR to allow sleeping until memory is available, or \fBKM_NOSLEEP\fR
to return \fINULL\fR immediately if memory is not available.
.RE

.SH DESCRIPTION
The \fBbioclone()\fR function returns an initialized buffer to perform
\fBI/O\fR to a portion of another buffer. The new buffer will be set up to
perform \fBI/O\fR to the range within the original \fBI/O\fR request specified
by the parameters \fIoff\fR and \fIlen\fR. An offset \fB0\fR starts the new
\fBI/O\fR request at the same address as the original request. \fIoff\fR +
\fIlen\fR must not exceed \fIb_bcount,\fR the length of the original request.
The device number \fIdev\fR specifies the device to which the buffer is to
perform \fBI/O\fR. \fIblkno\fR is the block number on device. It will be
assigned to the \fIb_blkno\fR field of the cloned buffer structure.
\fIiodone\fR lets the driver identify a specific \fBbiodone\fR(9F) routine to
be called by the driver when the \fBI/O\fR is complete. \fIbp_mem\fR determines
from where the space for the buffer should be allocated. If \fIbp_mem\fR is
\fBNULL\fR, \fBbioclone()\fR will allocate a new buffer using
\fBgetrbuf\fR(9F). If \fIsleepflag\fR is set to \fBKM_SLEEP\fR, the driver may
sleep until space is freed up. If \fIsleepflag\fR is set to \fBKM_NOSLEEP\fR,
the driver will not sleep. In either case, a pointer to the allocated space is
returned or \fINULL\fR to indicate that no space was available. After the
transfer is completed, the buffer has to be freed using \fBfreerbuf\fR(9F). If
\fIbp_mem\fR is not \fINULL\fR, it will be used as the space for the buffer
structure. The driver has to ensure that \fIbp_mem\fR is initialized properly
either using \fBgetrbuf\fR(9F) or \fBbioinit\fR(9F).
.sp
.LP
If the original buffer is mapped into the kernel virtual address space using
\fBbp_mapin\fR(9F) before calling \fBbioclone()\fR, a clone buffer will share
the kernel mapping of the original buffer. An additional \fBbp_mapin()\fR to
get a kernel mapping for the clone buffer is not necessary.
.sp
.LP
The driver has to ensure that the original buffer is not freed while any of the
clone buffers is still performing \fBI/O\fR. The \fBbiodone()\fR function has
to be called on all clone buffers \fBbefore\fR it is called on the original
buffer.
.SH RETURN VALUES
The \fBbioclone()\fR function returns a pointer to the initialized buffer
header, or \fBNULL\fR if no space is available.
.SH CONTEXT
The \fBbioclone()\fR function can be called from user, interrup, or interrupt
context. Drivers must not allow \fBbioclone()\fR to sleep if called from an
interrupt routine.
.SH EXAMPLES
\fBExample 1 \fRUsing \fBbioclone()\fR for Disk Striping
.sp
.LP
A device driver can use \fBbioclone()\fR for disk striping. For each disk in
the stripe, a clone buffer is created which performs \fBI/O\fR to a portion of
the original buffer.

.sp
.in +2
.nf
static int
stripe_strategy(struct buf *bp)
{
       ...
       bp_orig = bp;
       bp_1 = bioclone(bp_orig, 0, size_1, dev_1, blkno_1,
                       stripe_done, NULL, KM_SLEEP);
       fragment++;
       ...
       bp_n = bioclone(bp_orig, offset_n, size_n, dev_n,
                     blkno_n, stripe_done, NULL, KM_SLEEP);
       fragment++;
       /* submit bp_1 ... bp_n to device */
       xxstrategy(bp_x);
       return (0);
}

static uint_t
xxintr(caddr_t arg)
{
       ...
       /*
       * get bp of completed subrequest. biodone(9F) will
       * call stripe_done()
       */
       biodone(bp);
       return (0);
}

static int
stripe_done(struct buf *bp)
{
       ...
       freerbuf(bp);
       fragment--;
       if (fragment == 0) {
               /* get bp_orig */
               biodone(bp_orig);
       }
       return (0);
}
.fi
.in -2

.SH SEE ALSO
.BR biodone (9F),
.BR bp_mapin (9F),
.BR freerbuf (9F),
.BR getrbuf (9F),
.BR buf (9S)
.sp
.LP
\fIWriting Device Drivers\fR