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Path: utzoo!linus!decvax!harpo!eagle!mhuxl!houxm!ihnp4!zehntel!hplabs!hao!kpno!hsi!stevens
From: stevens@hsi.UUCP
Newsgroups: net.unix-wizards
Subject: read() from a tape
Message-ID: <120@hsi.UUCP>
Date: Tue, 8-Nov-83 08:23:48 EST
Article-I.D.: hsi.120
Posted: Tue Nov  8 08:23:48 1983
Date-Received: Sun, 13-Nov-83 10:30:42 EST
Organization: Health Systems Intl.  New Haven,CT
Lines: 22

On a VAX running 4.1bsd I found some code in a tape reading program
that went

	int length;

	length = read(tapefd, buf, 62000);
	if (length < 0)
		/* error */ ...
	if (length != -1)
		length &= 0xffff;

I removed the mask and sure enough, a read of a 3120 byte tape record
returned a length of 65536+3120, hence the mask was required.
I reduced the buffer size and the length to read to 30,000 bytes and
the returned value became 3120, so the mask was not needed.

Anyone know whats going on ?  (The tape driver is tm.c.)

	Richard Stevens
	Health Systems International, New Haven, CT
	{ decvax | hao | seismo | sdcsvax } ! kpno ! hsi ! stevens
                                             ihnp4 ! hsi ! stevens