linux-ext4 - Re: sparsify - utility to punch out blocks of 0s in a file

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Message-Id: <D9A6076F-154F-41A6-BC18-EC1AF2E73551@dilger.ca>
Date:	Sun, 5 Feb 2012 12:24:26 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Ron Yorston <rmy@...ress.co.uk>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: sparsify - utility to punch out blocks of 0s in a file

On 2012-02-05, at 10:23 AM, Eric Sandeen wrote:
> On 2/5/12 10:55 AM, Andreas Dilger wrote:
>> On 2012-02-05, at 9:36, Eric Sandeen <sandeen@...hat.com> wrote:
>>> On 2/5/12 3:33 AM, Ron Yorston wrote:
>>>> Eric Sandeen wrote:
>>>>> Now that ext4, xfs, & ocfs2 can support punch hole, a tool to
>>>>> "re-sparsify" a file by punching out ranges of 0s might be in order.
>>>>> 
>>>>> I'll see if util-linux wants it after it gets beat into shape.
>>>>> (or did a tool like this already exist and I missed it?)
>>> 
>>> Matthias' suggestion of adding SEEK_HOLE/SEEK_DATA makes very good sense too.
>> 
>> I thought about this, but if SEEK_HOLE/SEEK_DATA (or FIEMAP) worked,
>> then the file would already be sparse, so I don't think that will
>> help in this case...
> 
> But only if other tools originally used them, and there will probably be plenty
> of cases where they don't, or legacy files, or ....

I was thinking that the suggestion was to use SEEK_HOLE/SEEK_DATA to find
the holes in the file...  Of course, it makes a lot of sense if you use
them to skip the existing holes, and only look for strings of zeros in the
data parts...

Cheers, Andreas





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