bug#8490: dd reads random number of records from pipes (original) (raw)

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From: Eric Blake
Subject: bug#8490: dd reads random number of records from pipes - named or otherwise - coreutils 8.9
Date: Wed, 13 Apr 2011 09:13:59 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110318 Red Hat/3.1.9-3.el6_0 Mnenhy/0.8.3 Thunderbird/3.1.9

On 04/13/2011 08:39 AM, Bjartur Thorlacius wrote:

Have you looked into fullblock? If you only specify bs and count (and not ibs or obs) dd may fill the buffer partially. It'll do try to do count copies, but each copy may contain less data than expected. This sort of makes sense on HDDs or tapes with variable block sizes (where a read would return a whole block, but the block would be smaller than user specified bs). In this case dd will preserve the original block size. I've never encountered such an odditie — Or maybe I have, without noticing.

I think about noone that hasn't been involved in the development, in one way or another, gets this wrong (I don't quite get it yet). I think this should be changed, unless the user provids a hypothetical partblock option.

It can't be changed without changing POSIX.

-- Eric Blake address@hidden +1-801-349-2682 Libvirt virtualization library http://libvirt.org

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