GNU bug report logs - #21942
Files with incorrect file sizes

Previous Next

Full log

View this message in rfc822 format

From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stephan Müller <fruktopus <at> gmail.com>
Subject: bug#21942: closed (Re: [bug-diffutils] bug#21942: Files with
 incorrect file sizes)
Date: Sun, 06 Dec 2015 19:41:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#21942: Files with incorrect file sizes

which was filed against the diffutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 21942 <at> debbugs.gnu.org.

-- 
21942: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21942
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Jim Meyering <jim <at> meyering.net>
To: Stephan Müller <fruktopus <at> gmail.com>
Cc: 21942-done <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#21942: Files with incorrect file sizes
Date: Sun, 6 Dec 2015 11:39:44 -0800

On Sun, Dec 6, 2015 at 11:27 AM, Jim Meyering <jim <at> meyering.net> wrote:
...
> Thank you, but I don't want to have to specify some new option to
> avoid this misbehavior, so will push the attached patch shortly.
> If someone finds a system for which a falsely reported stat.st_size
> is nonzero, we can revisit this.

Pushed with commit log changes and one fewer blank line in NEWS.

[Message part 3 (message/rfc822, inline)]

From: Stephan Müller <fruktopus <at> gmail.com>
To: bug-diffutils <at> gnu.org
Subject: Files with incorrect file sizes
Date: Tue, 17 Nov 2015 12:44:08 +0100

Hi there,

recently I had to debug weird problem. Finally I figured it out.

Virtual file systems like /sys or /proc usually don't care about file
sizes. All files have a size of 0. This leads to difficulties as diff
sometimes looks for file sizes.

Say you do:

> $ cp /proc/cmdline my_cmdline
> $ diff /proc/cmdline my_cmdline ; echo $?
> 0      // ok, files don't differ
> $ diff --brief /proc/cmdline my_cmdline
> Files /proc/cmdline and mycmdline differ  

The --brief option triggers a binary compare, as we aren't interested
in the actual differences this makes sense. As a first step, file sizes
are compared (0 vs ~150) and the files are reported as different.

I am not sure how to fix this. I.e. are the files different or not? What
is the correct behavior. In any case --brief should have no influence on
the overall result! I see the following options (I prefer the 2nd):

1: Don't use file sizes in comparing. This is rather expensive but
would certainly fix it.

2: add a --use-file-sizes flag which enables decisions
based on file sizes. Without this flag, always look into the files.
And --brief should report, if the files differ because of their data or
size. That is 

> $ diff /proc/cmdline my_cmdline ; echo $?
> 0      // ok, files don't differ  

> $ diff --brief /proc/cmdline my_cmdline ; echo $0
> 0  

> $ diff --brief --use-file-sizes /proc/cmdline my_cmdline
> Files /proc/cmdline and mycmdline differ in file size  

3: Leave it at it is and add a warning in the man page. However that
would be very inconvenient.


   best, stephan

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.