Subject: Re: bug#13135: Loss of data while copying

From: Eric Blake <[email-masked]>
Date: Mon, 10 Dec 2012 08:09:44 -0700

tag 13135 notabug
thanks

On 12/10/2012 07:58 AM, Cojocaru Alexandru wrote:
> bash$ yes $(for i in $(seq 1 100000); do echo -n a; done) | dd of=big-lines ibs=100001 count=10000
> 9924+76 records in

Thanks for the report.  Based on this output, short reads occurred.  dd
transferred exactly 10000 reads as requested, but since some of those
were short, it transferred less than 10000*100001 bytes.  This is
expected (and the behavior is described in that way by POSIX); the
solution you are looking for is to _also_ use the iconv=fullblock
option, to force dd to re-read until it has a full input block rather
than immediately transferring short input reads to output.

As such, I'm closing this as not a bug.  Do feel free to add further
comments to this thread, though, if you have more questions about why dd
does this.

Oh, and by the way, 'echo -n' is not portable.  You want to use
printf(1) instead.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org