linux-ext4 - Re: [PATCH] common/defrag: rework _require

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Message-ID: <20160811174802.GC31540@infradead.org>
Date:	Thu, 11 Aug 2016 10:48:02 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Eric Whitney <enwlinux@...il.com>
Cc:	fstests@...r.kernel.org, linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] common/defrag: rework _require_defrag for ext4

On Thu, Aug 04, 2016 at 04:02:46PM -0400, Eric Whitney wrote:
> The existing _require_defrag function rejects ext4 file systems
> mounted with the dax option or constructed without extents.  However,
> there are also a number of other ext4 file system configuration cases
> that do not currently support online defrag, including encryption, data
> journaling, and bigalloc.  In the future, online defrag functionality
> may be implemented for some of these, and new configuration cases
> could be added that don't support it.
> 
> Rather than add a laundry list of mount and file system configuration
> options to the existing _require_defrag function that will need ongoing
> maintenance, use the available src/e4compact program to directly
> determine whether the kernel supports ext4's move extent ioctl on the
> test file system.

This look reasonable - but I wonder if we could just come up with an
even more generic version that uses your approach on all file systems,
so that the only per-fs logic left would be to apply the
DEFRAG_PROG variable.
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