Fragmented Commands

Single I/O requests larger than the maximum transfer size must be divided into smaller requests by the SCSI device driver.

For calls to a SCSI device driver's character I/O (read/write) entry points, the uphysio kernel service can be used to break up these requests. For a fragmented command such as this, the sc_buf.bp field should be null so that the SCSI adapter device driver uses only the information in the sc_buf structure to prepare for the DMA operation.