bioclone(9F) Kernel Functions for Drivers bioclone(9F)
NAME
bioclone - 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
bioclone() 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 specific 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 getr-
buf(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
bioclone() can be called from user 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 por-
tion 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 ALSO
biodone(9F), bp_mapin(9F), freerbuf(9F), getrbuf(9F), buf(9S)
Writing Device Drivers
SunOS 5.10 20 Nov 1996 bioclone(9F)