Date: Sat, 30 Sep 2006 21:51:45 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Helmut Schellong <var@schellong.biz> Cc: freebsd-bugs@freebsd.org, freebsd-gnats-submit@freebsd.org Subject: Re: bin/103845: sha256 /dev/acd0 returns immediately Message-ID: <20060930205828.M926@epsplex.bde.org> In-Reply-To: <200609300624.k8U6O9TM017192@www.freebsd.org> References: <200609300624.k8U6O9TM017192@www.freebsd.org>
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On Sat, 30 Sep 2006, Helmut Schellong wrote: >> Description: > sha256 /dev/acd0 returns *immediately* > with a wrong checksum. > > CD content is BETA1-disc1. > > dd if=/dev/acd0 of=/usr/z bs=4b; sha256 /usr/z; rm /usr/z > works fine. md5(1) and friends haven't worked for files specified on the command line since 2001. At least for md5, this is due to a bug in libmd. MDXFileChunk() has been used to implement MDXFile() since 2001, but MDXFileChunk() cannot be used for this since it assumes that the file is a regular file (or perhaps a symlink) so that st_size is valid and the file is seekable. One workaround is to run md5 on 1 file at a time and not specify the file on the command line. "md5 </dev/acd0" works because it uses the "filter" cases which doesn't go near the buggy code. Another workaround is to use a pipeline: "cat /dev/acd0 | md5". For pipes, it is essential that md5 act as a filter. However, the previous workaround is better if you don't start with a pipe. The workaround can also be used backwards to break the case where the file or pipe is already open: "md5 /dev/stdin </dev/acd0" gives the checksum of an empty file. Bruce
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