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Date: Mon, 18 Nov 2019 01:30:55 +0800
To: Pratik Shinde <pratikshinde320@gmail.com>
Subject: Re: Support for uncompressed sparse files.
Message-ID: <20191117173027.GA21516@hsiangkao-HP-ZHAN-66-Pro-G1>
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From: Gao Xiang via Linux-erofs <linux-erofs@lists.ozlabs.org>
Reply-To: Gao Xiang <hsiangkao@aol.com>
Cc: linux-erofs@lists.ozlabs.org
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Sender: "Linux-erofs"
 <linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org>

Hi Pratik,

On Sun, Nov 17, 2019 at 03:40:43PM +0530, Pratik Shinde wrote:
> Hello Gao,
> 
> I have started working on above functionality for erofs.
> First thing we need to do is detect sparse files & determine location of
> holes in it.
> 
> I was thinking of using lseek() with SEEK_HOLE & SEEK_DATA for detecting
> holes.
> Let me know what you think about the approach OR any other better approach
> in your mind.
> 
> PS : support for SEEK_HOLE & SEEK_DATA came in 3.4 kernel.

That is a good start to detect sparse files by SEEK_HOLE & SEEK_DATA.

And as the first step, we need to design the on-disk extent format
for uncompressed sparse files. Is there some preliminary proposed
ideas for this as well? :-) (I'm not sure whether Chao is busy in
other stuffs now, we'd get in line with sparse on-disk format.)

Thanks,
Gao Xiang