The Linux 2.4 SCSI subsystem HOWTO
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# B.5. sg changes

The main change is the addition of a new interface structure called "sg_io_hdr". The existing interface structure (called "sg_header") was found to be inflexible requiring the concatenation of raw data together with meta-data in the read() and write() commands.

    sg_io_hdr          {new interface structure}
    SG_IO              {new ioctl}
    direct IO          {present but commented out, see ALLOW_DIO}
    procfs output      {new information in /proc/scsi/sg directory}
    boot/module parameters  {new}

Up to 64 bytes of sense data can be obtained from the sg_io_hdr interface structure. Also a residual count associated with the data transfer is available (if the lower level driver supports it, if not the residual count will be 0).

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