User Guide

Ampex 1308911-02 B-23
Device Special Files Introduction
DST_SYNC_WRITE
Synchronize tape drive
buffer after write
(Ox0001000)
When set to on, automatically flushes tape drive buffer to tape after each write
data command. When set to off, does not flush tape drive buffer after a write data
command.
Note: The DST_NO_FLUSH parameter controls tape drive behavior when a write
filemark command is issued.
By default, open sets this parameter to off. When O_SYNC is set in the flags
argument of the open call, however, this parameter is set to on and write data
commands do not return until the data has been physically written to the tape.
Note: When Early Warning is detected, drive behavior is controlled by the
DST_ZERO_ON_EW
parameter.
DST_WRITE_PROT
Write protect cartridge
(Ox0040000)
This parameter reports status only. When set to on, it indicates the cartridge is
write-protected.
DST_ZERO_ON_EW
Report zero bytes on I/O
after early warning
(Ox0004000)
On — When Early Warning is detected during a write, flushes tape drive buffer to
tape and reports zero bytes.
Off — When Early Warning is detected during a read or write, returns a value of
-1 and sets
errno to ENOSPC after flushing the data buffer to tape. (If flushing of
the tape drive buffer to tape is unsuccessful, the drive returns the number of bytes
written to tape.)
DST_ZERO_ON_FM
Report zero bytes on read
after filemark
(Ox0002000)
When the tape drive detects a filemark during a read operation, it returns the
number of bytes read and sets the current position after the filemark.
• If this parameter is set to on, the read operation "always" returns zero to
indicate EOF (End of File).
When a filemark is detected during a read operation, the read returns the
actual number of bytes transferred. If the number of bytes transferred is less
than requested, then the next read operation returns zero. If the number of
bytes transferred is zero (i.e. no data transfer because the current position is
just before filemark), then this already indicate an EOF condition so the next
read operation does not require to return zero. If this parameter is set to off or
the filemark was detected before any data was read, the next read operation
gets data from the next file (if not at End of Data or a null file).
• If this parameter is set to off, the read operation returns number of bytes less
than requested to indicate EOF.
When a filemark is detected during a read operation, the read returns the
actual number of bytes transferred. If the number of bytes transferred is less
than the number of bytes requested or is zero, this implies the EOF condition
so the next read operation (if successful) immediately returns data (if any)
from the next file.
Table B-8. Device Special File Interface Parameter Description (Continued)
Mnemonic
Name (Bit Location)
Description