[debbugs-tracker] bug#13135: closed (Loss of data while copying)

[GNU bug Tracking System]

Your message dated Mon, 10 Dec 2012 08:09:44 -0700
with message-id <address@hidden>
and subject line Re: bug#13135: Loss of data while copying
has caused the debbugs.gnu.org bug report #13135,
regarding Loss of data while copying
to be marked as done.

(If you believe you have received this mail in error, please contact
address@hidden)


-- 
13135: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13135
GNU Bug Tracking System
Contact address@hidden with problems
> --- Begin Message ---
>
>
>
> Subject: 
>
> Loss of data while copying
>
>
>
>
> Date: 
>
> Mon, 10 Dec 2012 15:58:48 +0100
>
>
>
>
> bash$ yes $(for i in $(seq 1 100000); do echo -n a; done) | dd of=big-lines 
> ibs=100001 count=10000
> 9924+76 records in
> 1951183+1 records out
> *999005921* bytes (999 MB) copied, 21.6135 s, 46.2 MB/s
>
> bash$ yes $(for i in $(seq 1 100000); do echo -n a; done) | dd of=big-lines 
> ibs=100001 count=10000
> 9887+113 records in
> 1950792+1 records out
> *998805894* bytes (999 MB) copied, 21.3409 s, 46.8 MB/s
>
> bash$ yes $(for i in $(seq 1 100000); do echo -n a; done) | dd of=big-lines 
> ibs=100001 count=10000
> 9890+110 records in
> 1950792+1 records out
> *998805919* bytes (999 MB) copied, 21.5801 s, 46.3 MB/s
>
> bash$ yes $(for i in $(seq 1 100000); do echo -n a; done) | dd of=big-lines 
> ibs=100001 count=10000
> 9884+116 records in
> 1950011+1 records out
> *998405915* bytes (998 MB) copied, 25.2695 s, 39.5 MB/s
>
> WTF?!
>
> Best regards,
> Cojocaru Alexandru
>
>
>
> --- End Message ---

--- Begin Message --- Subject: Re: bug#13135: Loss of data while copying Date: Mon, 10 Dec 2012 08:09:44 -0700 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0

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

signature.asc
Description: OpenPGP digital signature

--- End Message ---