Data file and tape Input and Output

data_read(fd,event,eventSize)

data_read_alloc(fd,*event)

Purpose:

Arguments:

Return Value:

• DATAIO_OK --- success- a data record was read int the buffer
• DATAIO_EOF --- filemark or end of data. When reading from tapes on some systems (notably IBM RS6000 AIX3 and AIX4), an end-of-data cannot be distinguished from an infinite number of filemarks.
• DATAIO_EOT --- end of tape/end of data.
• DATAIO_ERROR --- read error. When reading tapes, possible causes for this return code might be tape medium errors, tape drive failures and scsi bus resets.
• DATAIO_BADCRC --- when writing data records, the dataIO library always adds a control checksum (CRC-32) to the data. When reading the data records, the library routines recalculate this checksum and compare it with the value in the data. This enables it to discover if the data becomes corrupted between the write and read operations. How can the data get corrupted? The data on the tape and on the disk is protected by various ECC (error-correction) schemes that can detect and correct multi-bit errors enabling the tape and disk drives to transparently perform error correction. However the data going over the SCSI bus is protected only by parity checks, which can detect only single bit errors and in at least one case we had a bad Exabyte EXB-8500 tape drive that was consistently corrupting data. The data returned with the DATAIO_BADCRC error should be discarded.

data_write(fd,event)

Purpose:

Arguments:

Return Value:

data_flush(fd)

Purpose:

Arguments:

Return Value:

data_writeFM(fd)

Purpose:

• write a filemark on the tape.

Arguments:

• fd --- file descriptor for the opened tape device

Return Value:

data_findFM(fd)

Purpose:

Arguments:

Return Value:

data_SeekTape(fd,runNo,*tapeNo)

Purpose:

Arguments:

Return Value:

Author: K.Olchanski, 1996-Apr-13