SCO OpenServer

strategy(D2oddi)

strategy -- handle block device input and output

Synopsis

   void prefixstrategy (struct buf *bp);

Description

The strategy( ) entry point routine handles the data transfer through the buffer cache that is used by block devices. Block drivers must include a strategy( ) routine to initiate the transfer, validate the buffer header information, and generate the device operations required to start the data transfer.

Arguments

buf: pointer to a buf data structure.
The pointer is the address of an instance of the buf data structure that is defined in the <sys/buf.h> header file. All information about the data transfer is contained in this structure. The pointer is also used to return status and error information to the kernel and convey the information to the user.

Return values

None

Usage

The strategy( ) routine should perform the following activities:

Get and validate the device number
Schedule block I/O requests
Call subordinate driver routines (if any) to notify a controller than an I/O operation is waiting
If the device can only handle one I/O operation at a time, the strategy( ) routine must cause the process to sleep until the device is available. For example, a sequential access device such as a tape drive should handle only one read/write operation at a time.
Handle any errors occurring during the read/write operation
Log device errors to the hard disk error log

If an error occurs, set the b_error member of the buf structure and OR the B_ERROR flag into the b_flags member. The test should be for B_READ and ``not'' B_READ . B_WRITE cannot be tested because it is not a flag, it is 0. You must also supply a print(D2oddi) routine for the kernel to call to output a message to the console and putbuf structure.

Context and synchronization

Blockable context. The driver can block but cannot do operations such as copyout(D3) that require access to the requesting process's address space. context

Hardware applicability

All

Version applicability

oddi: 1, 2, 2mp, 3, 3mp, 4, 4mp, 5, 5mp, 6, 6mp

SVR5 DDI compatibility

The strategy(D2) entry point routine provides the same functionality for DDI versions prior to DDI 8. Beginning with DDI 8, use the biostart(D2) entry point routine for both block and raw access I/O operations.

External dependencies

Drivers that contain a strategy( ) routine must have a b in the second column of the mdevice(F) file to indicate that it is a block device. The kernel expects a strategy( ) routine for every block driver that is configured.

References

print(D2oddi)

``Buffered I/O buffers, allocating'' in HDK Technical Reference
``Block device drivers'' in HDK Technical Reference