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strategy(9e) [bsd man page]

strategy(9E)							Driver Entry Points						      strategy(9E)

NAME
strategy - perform block I/O SYNOPSIS
#include <sys/types.h> #include <sys/buf.h> #include <sys/ddi.h> #include <sys/sunddi.h> int prefixstrategy(struct buf *bp); INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI). This entry point is required for block devices. PARAMETERS
bp Pointer to the buf(9S) structure. DESCRIPTION
The strategy() routine is called indirectly (through cb_ops(9S)) by the kernel to read and write blocks of data on the block device. strat- egy() may also be called directly or indirectly to support the raw character interface of a block device (read(9E), write(9E) and ioctl(9E)). The strategy() routine's responsibility is to set up and initiate the transfer. In general, strategy() should not block. It can, however, perform a kmem_cache_alloc(9F) with both the KM_PUSHPAGE and KM_SLEEP flags set, which might block, without causing deadlock in low memory situations. RETURN VALUES
The strategy() function must return 0. On an error condition, it should call bioerror(9f) to set b_flags to the proper error code, and call biodone(9f). Note that a partial transfer is not considered to be an error. SEE ALSO
ioctl(9E), read(9E), write(9E), biodone(9F), bioerror(9F), buf(9S), cb_ops(9S), kmem_cache_alloc(9F) Writing Device Drivers SunOS 5.10 6 Nov 2003 strategy(9E)

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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)

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