BIOCLONE(9F)BIOCLONE(9F)NAMEbioclone - clone another buffer
SYNOPSIS
#include <sys/ddi.h>
#include <sys/sunddi.h>
struct buf *bioclone(struct buf *bp, off_t off, size_t len, dev_t dev,
daddr_t blkno, int (*iodone) (struct buf *), struct buf *bp_mem,
int sleepflag);
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI).
PARAMETERS
bp
Pointer to the buf(9S) structure describing the original
I/O request.
off
Offset within original I/O request where new I/O request
should start.
len
Length of the I/O request.
dev
Device number.
blkno
Block number on device.
iodone
Specific biodone(9F) routine.
bp_mem
Pointer to a buffer structure to be filled in or NULL.
sleepflag
Determines whether caller can sleep for memory. Possible
flags are KM_SLEEP to allow sleeping until memory is
available, or KM_NOSLEEP to return NULL immediately if
memory is not available.
DESCRIPTION
The bioclone() function returns an initialized buffer to perform I/O to
a portion of another buffer. The new buffer will be set up to perform
I/O to the range within the original I/O request specified by the
parameters off and len. An offset 0 starts the new I/O request at the
same address as the original request. off + len must not exceed
b_bcount, the length of the original request. The device number dev
specifies the device to which the buffer is to perform I/O. blkno is
the block number on device. It will be assigned to the b_blkno field of
the cloned buffer structure. iodone lets the driver identify a spe‐
cific biodone(9F) routine to be called by the driver when the I/O is
complete. bp_mem determines from where the space for the buffer should
be allocated. If bp_mem is NULL, bioclone() will allocate a new buffer
using getrbuf(9F). If sleepflag is set to KM_SLEEP, the driver may
sleep until space is freed up. If sleepflag is set to KM_NOSLEEP, the
driver will not sleep. In either case, a pointer to the allocated space
is returned or NULL to indicate that no space was available. After the
transfer is completed, the buffer has to be freed using freerbuf(9F).
If bp_mem is not NULL, it will be used as the space for the buffer
structure. The driver has to ensure that bp_mem is initialized properly
either using getrbuf(9F) or bioinit(9F).
If the original buffer is mapped into the kernel virtual address space
using bp_mapin(9F) before calling bioclone(), a clone buffer will share
the kernel mapping of the original buffer. An additional bp_mapin() to
get a kernel mapping for the clone buffer is not necessary.
The driver has to ensure that the original buffer is not freed while
any of the clone buffers is still performing I/O. The biodone() func‐
tion has to be called on all clone buffers before it is called on the
original buffer.
RETURN VALUES
The bioclone() function returns a pointer to the initialized buffer
header, or NULL if no space is available.
CONTEXT
The bioclone() function can be called from user, interrup, or interrupt
context. Drivers must not allow bioclone() to sleep if called from an
interrupt routine.
EXAMPLES
Example 1 Using bioclone() for Disk Striping
A device driver can use bioclone() for disk striping. For each disk in
the stripe, a clone buffer is created which performs I/O to a portion
of the original buffer.
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);
}
SEE ALSObiodone(9F), bp_mapin(9F), freerbuf(9F), getrbuf(9F), buf(9S)
Writing Device Drivers
Jan 16, 2006 BIOCLONE(9F)
