linux-kernel - Re: How does ext2 implement sparse files?

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Message-ID: <20080131165117.GC26259@csclub.uwaterloo.ca>
Date:	Thu, 31 Jan 2008 11:51:17 -0500
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Lars Noschinski <lklml@...noschinski.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How does ext2 implement sparse files?

On Thu, Jan 31, 2008 at 04:28:23PM +0100, Lars Noschinski wrote:
> For an university project, we had to write a toy filesystem (ext2-like),
> for which I would like to implement sparse file support. For this, I
> digged through the ext2 source code; but I could not find the point,
> where ext2 detects holes.
> 
> As far as I can see from fs/buffer.c, an hole is a buffer_head which is
> not mapped, but uptodate. But I cannot find a relevant source line,
> where ext2 makes usage of this information.
> 
> Any hints would be greatly appreciated,

While I don't actually know, I always thought it was up to the
application to create files with holes by seeking over the holes before
writing data.  That seems like the simplest way to me.

--
Len Sorensen
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