bioclone man page on SmartOS

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       bioclone - clone another buffer

       #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);

       Solaris DDI specific (Solaris DDI).

		    Pointer  to	 the buf(9S) structure describing the original
		    I/O request.

		    Offset within original I/O request where new  I/O  request
		    should start.

		    Length of the I/O request.

		    Device number.

		    Block number on device.

		    Specific biodone(9F) routine.

		    Pointer to a buffer structure to be filled in or NULL.

		    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.

       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.

       The  bioclone()	function  returns  a pointer to the initialized buffer
       header, or NULL if no space is available.

       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.

       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);
		bp_n = bioclone(bp_orig, offset_n, size_n, dev_n,
			      blkno_n, stripe_done, NULL, KM_SLEEP);
		/* submit bp_1 ... bp_n to device */
		return (0);

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

	 static int
	 stripe_done(struct buf *bp)
		if (fragment == 0) {
			/* get bp_orig */
		return (0);

       biodone(9F), bp_mapin(9F), freerbuf(9F), getrbuf(9F), buf(9S)

       Writing Device Drivers

				 Jan 16, 2006			  BIOCLONE(9F)

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