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Date:      Fri, 05 Nov 1999 09:15:46 -0800
From:      John Hanley <jh@yahoo-inc.com>
To:        Jan Pechanec <pechy@hp735.cvut.cz>
Cc:        Erez Zadok <ezk@cs.columbia.edu>, Robert Watson <robert+freebsd@cyrus.watson.org>, freebsd-fs@FreeBSD.ORG
Subject:   deadfs, Re: stupidfs - easily extensible test file systems?
Message-ID:  <199911051715.JAA23410@parker.yahoo.com>
In-Reply-To: Your message of "Fri, 05 Nov 1999 15:23:22 %2B0100." <Pine.SGI.4.05.9911051518180.10246-100000@akat.civ.cvut.cz> 

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>	BTW, don't you know why deadfs was written? No doc in FreeBSD.
> From what I saw in the source code, operations just fail.

Deadfs is so you can V_BAD a vnode to revoke access to a tty or pty.
(Or revoke access to a filesystem, upon forcible umount.)
There used to be an ugly security problem where someone would log in,
start background jobs that can read/write a tty or pty, their login shell
exits, and some hapless person logs on to the tty or pty and is abused
by the background jobs that still hold an open file descriptor.
Nowadays, upon logout we V_BAD those file descriptors and the background
jobs can do no harm, but they are allowed to finish their computations
and write their results to disk.


	Cheers,
	JH


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