From mboxrd@z Thu Jan  1 00:00:00 1970
From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH RFC] ext4: collapse a single extent tree block into the
 inode if possible
Date: Thu, 9 Aug 2012 09:07:54 -0400
Message-ID: <20120809130754.GB4511@thunk.org>
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Here's a test script which demonstrates how we can up with an external
extent tree block containing a single extent.  It needs to run as root
since it will be mounting a test file system image on /mnt.


#!/bin/bash
fs=/u1/test-fs.img
num=128
max=$(expr $num \* 8)
size=$(expr $num \* 32)k

dd if=/dev/zero of=$fs bs=4k count=$(expr $max \* 4)

mke2fs -t ext4 -b 4096 -qF $fs
mount -t ext4 $fs /mnt

cd /mnt
fallocate -l $size test-file
for i in $(seq 0 8 $max | sed -e '$d') ; do
	dd if=/dev/zero of=test-file conv=notrunc,nocreat bs=4k \
	   seek=$i count=1 > /dev/null 2>&1
done
sync

dd if=/dev/zero of=test-file conv=notrunc,nocreat \
	bs=4k count=$max > /dev/null 2>&1
sync
cd /

umount /mnt
debugfs $fs -R "stat test-file"