NAME
    CMD_WRITE/ETD_WRITE -- write sectors of data to a disk.

FUNCTION
    These commands transfer data from a supplied buffer to the track
    buffer. If the track that contains this sector is already in the track
    buffer, no disk activity is initiated. If the desired sector is not in
    the buffer, the track containing that sector is automatically read in.
    If the data in the current track buffer has been modified, it is
    written out to the disk before the new track is read in for
    modification. ETD_WRITE will write the sector label area if
    iotd_SecLabel is non-NULL.

IO REQUEST INPUT
    io_Device       preset by the call to opendevice()
    io_Unit         preset by the call to opendevice()
    io_Command      CMD_WRITE or ETD_WRITE
    io_Flags        0 or IOF_QUICK
    io_Data         pointer to the buffer where the data should be put
    io_Length       number of bytes to write, must be a multiple of
                    TD_SECTOR.
    io_Offset       byte offset from the start of the disk describing
                    where to write data to, must be a multiple of
                    TD_SECTOR.
    iotd_Count      (ETD_WRITE only) maximum allowable change counter
                    value.
    iotd_SecLabel   (ETD_WRITE only) NULL or sector label buffer pointer.
                    If provided, the buffer must be a multiple of
                    TD_LABELSIZE.

IO REQUEST RESULT
    io_Error - 0 for success, or an error code as defined in
               <devices/trackdisk.h>

NOTES
    Under versions of Kickstart earlier than V36, the io_Data had to
    point to a buffer in chip memory. This restriction is no longer
    present as of Kickstart V36 and beyond.

SEE ALSO
    cmd_read, td_format