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To: freebsd-bugs@freebsd.org
Subject: mv truncates files
Reply-To: yuhara@flab.fujitsu.co.jp
From: yuhara@flab.fujitsu.co.jp
Date: Wed, 06 Sep 1995 15:37:20 +0900
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Bug Report: cross device "mv" corrupts files

FreeBSD version: 2.1.0-SNAP-950726

File: /usr/src/bin/mv/mv.c

Symptom: If a owner of a file is not a member of the group ID of the
	 source file, cross device "mv" by the owner sometimes TRUNCATES
	 the file, especially when the destination is in a NFS mounted
	 directory.
	 The source file is deleted so there is no way to retrieve the lost
	 data!!

Detail: 
    For cross device "mv", "mv" opens the source and the
    destination, copies data, closes the source, changes uid/gid/mode
    of the destination (fchown(), fchmod()), and then closes the destination.
    Problem occurs when fchown() fails.

    My guess: When an error occurs during fchown(), the written data that
		is in the buffer cache but not yet transferred to a disk
		is regarded as erronous and is abandoned in the kernel.

		Either the filesystem or "mv" is wrong.
		Since I don't know the intended semantics of the
		filesystem of FreeBSD, I can't say which is wrong.

		If "mv" is the culprit, the fix seems to be simple.
		Close the destination just after the copy.
		Use chown(), chmod() instead of fchown(), fchmod().

(I'm not on the mailing lists. Please include my address in your reply.)

------
Masanobu Yuhara		yuhara@flab.fujitsu.co.jp
Fujitsu Laboratories Ltd.