linux-ext4 - Re: Determining if an ext4 fs uses the whole partition

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Message-ID: <20120430173304.GF6938@tux1.beaverton.ibm.com>
Date:	Mon, 30 Apr 2012 10:33:04 -0700
From:	djwong <djwong@...ibm.com>
To:	Daniel Drake <dsd@...top.org>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Determining if an ext4 fs uses the whole partition

On Mon, Apr 30, 2012 at 11:19:31AM -0600, Daniel Drake wrote:
> Hi,
> 
> OLPC has started using ext4 online resizing to grow our filesystems to
> use the whole SD card on first boot - something we never did before.
> Working very nicely, thanks!
> 
> I'm trying to simplify/improve the scripts involved in doing this.
> 
> How can I programatically check if an ext4 fs already fills its
> partition, or if it has room to grow?

Is it not the case that there's room to grow if:

(ext4_block_count * ext4_block_size) - (bdev_size * 512) >= ext4_block_size

> The numbers produced by dumpe2fs (e.g. block count) or "df" don't seem
> to exactly line up with the sizes produced by fdisk.

How far off are the counts?  A small number of sectors, or many?

--D

> One easy solution, if possible, would be to find out the number of the
> last sector used by the filesystem. I could then very easily compare
> this to the "end" information found in sysfs for the partition. Then I
> can make the decision on whether to grow or not.
> 
> Thanks
> Daniel
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