linux-ext4 - Re: Question about ext4 testing: need to produce a high depth extent tree to verify mapping code

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Date:   Fri, 05 Jul 2019 11:49:02 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Parisc List <linux-parisc@...r.kernel.org>
Subject: Re: Question about ext4 testing: need to produce a high depth
 extent tree to verify mapping code

On Fri, 2019-07-05 at 10:39 -0700, Matthew Wilcox wrote:
> On Fri, Jul 05, 2019 at 09:25:48AM -0700, James Bottomley wrote:
> > Now the problem: I'd like to do some testing with high depth extent
> > trees to make sure I got this right, but the files we load at boot
> > are ~20MB in size and I'm having a hard time fragmenting the
> > filesystem enough to produce a reasonable extent (I've basically
> > only got to a two level tree with two entries at the top).  Is
> > there an easy way of producing a high depth extent tree for a 20MB
> > file?
> 
> Create a series of 4kB files numbered sequentially, each 4kB in size
> until you fill the partition.  Delete the even numbered ones.  Create
> a 20MB file.

Well, I know *how* to do it ... I was just hoping, in the interests of
creative laziness, that someone else had produced a script for this
before I had to ... particularly one which leaves more randomized gaps.

James