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


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


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

void biodone(struct buf *bp);


Architecture independent level 1 (DDI/DKI).


Pointer to a buf(9S) structure.


The biodone() function 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
buffer I/O request is complete.

The biodone() function 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.


The biodone() function can be called from user, interrupt, or kernel


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 */
5 static int
6 ramdstrategy(struct buf *bp)
7 {
8 daddr_t blkno = bp->b_blkno; /* get block number */
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 */
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 }


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

Writing Device Drivers


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.


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.

January 16, 2006 BIODONE(9F)