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From: HBO043%DJUKFA11.BITNET@cunyvm.cuny.edu (Christoph van Wuellen)
Newsgroups: comp.os.minix
Subject: ERROR in ST MINIX printer driver.
Message-ID: <55322@nigel.ee.udel.edu>
Date: 3 Jun 91 08:24:12 GMT
Sender: usenet@ee.udel.edu
Lines: 18

I discovered the following error in the ST MINIX printer driver. It took
quite a while to spot it.

The st printer driver handles valid requests (TTY_WRITE, CANCEL, HARD_INT),
but simply ignores invalid requests in order to reply with EINVAL.

Now, if you do isatty(fd), where fd is connected to /dev/lp, the whole
system hangs: FS sends a message with TTY_IOCTL to PRINTER, and PRINTER
does not respond. This results in FS waiting for PRINTER and PRINTER
waiting for ANY -- a deadlock.

This happens, e.g., if you have ls(1) compiled without defining ONECOLUMN,
and if you do ls -l > /dev/lp

The fix is simply to call 'reply' with EINVAL.

I have plain ST-1.5 adopted to my hardware, so I do not know if it has been
fixed. -- C.v.W.