biodone(9F)						   Kernel Functions for Drivers 					       biodone(9F)

NAME

       biodone - release buffer after buffer I/O transfer and notify blocked threads

SYNOPSIS

       #include <sys/types.h>
       #include <sys/buf.h>

       void biodone(struct buf *bp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       bp	Pointer to a  buf(9S) structure.

DESCRIPTION

       biodone()  notifies  blocked processes waiting for the I/O to complete, sets the B_DONE flag in the b_flags field of the buf(9S) structure,
       and releases the buffer if the I/O is asynchronous. biodone() is called by either the driver interrupt or strategy(9E) routines when a buf-
       fer I/O request is complete.

       biodone() provides the capability to call a completion routine if  bp describes a kernel buffer. The address of the routine is specified in
       the b_iodone field of the buf(9S) structure.
	If such a routine is specified, biodone() calls it and returns without performing any other actions.  Otherwise,  it  performs	the  steps
       above.

CONTEXT

       biodone() can be called from user or interrupt context.

EXAMPLES

       Generally, the first validation test performed by any block device strategy(9E) routine is a check for an end-of-file (EOF) condition.  The
       strategy(9E) routine is responsible for determining an EOF condition when the device is accessed directly.  If a read(2)  request  is  made
       for  one block beyond the limits of the device (line 10), it will report an EOF condition.  Otherwise, if the request is outside the limits
       of the device, the routine will report an error condition.
	In either case, report the I/O operation as complete (line 27).

	1   #define RAMDNBLK	1000 /* Number of blocks in RAM disk */
	2   #define RAMDBSIZ	512  /* Number of bytes per block */
	3   char ramdblks[RAMDNBLK][RAMDBSIZ]; /* Array containing RAM disk */
	4
	5   static int
	6   ramdstrategy(struct buf *bp)
	7   {
	8      daddr_t blkno = bp->b_blkno;    /* get block number */
	9
       10      if ((blkno < 0) || (blkno >= RAMDNBLK)) {
       11	     /*
       12	      * If requested block is outside RAM disk
       13	      * limits, test for EOF which could result
       14	      * from a direct (physio) request.
       15	      */
       16	     if ((blkno == RAMDNBLK) && (bp->b_flags & B_READ)) {
       17	      /*
       18	       * If read is for block beyond RAM disk
       19	       * limits, mark EOF condition.
       20	       */
       21	       bp->b_resid = bp->b_bcount;  /* compute return value */
       22
       23	    } else {	/* I/O attempt is beyond */
       24	       bp->b_error = ENXIO;    /*    limits of RAM disk */
       25	       bp->b_flags |= B_ERROR; /* return error */
       26	    }
       27	    biodone(bp);     /* mark I/O complete (B_DONE) */
       28	      /*
       29	       * Wake any processes awaiting this I/O
       30	       * or release buffer for asynchronous
       31	       * (B_ASYNC) request.
       32	       */
       33	    return(0);
       34      }
		  ...

SEE ALSO

       read(2), strategy(9E), biowait(9F), ddi_add_intr(9F), delay(9F), timeout(9F), untimeout(9F), buf(9S)

       Writing Device Drivers

WARNINGS

       After calling  biodone(), bp is no longer available to be referred to by the driver. If the driver makes any reference to  bp after calling
       biodone(), a panic may result.

NOTES

       Drivers	that use the b_iodone field of the buf(9S) structure to specify a substitute completion routine should save  the value of b_iodone
       before changing it, and then restore the old value before calling biodone() to release the buffer.

SunOS 5.10							    23 Apr 1996 						       biodone(9F)