linux-kernel - Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

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Message-ID: <20101117063125.GE5618@dhcp231-156.rdu.redhat.com>
Date:	Wed, 17 Nov 2010 01:31:26 -0500
From:	Josef Bacik <josef@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>, Avi Kivity <avi@...hat.com>,
	Josef Bacik <josef@...hat.com>, david@...morbit.com,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	xfs@....sgi.com, cmm@...ibm.com, cluster-devel@...hat.com,
	ocfs2-devel@....oracle.com
Subject: Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

On Tue, Nov 16, 2010 at 10:06:40PM -0500, Ted Ts'o wrote:
> > >There is no simple way to test if a filesystem supports hole punching or not so
> > >the check has to be done per fs.  Thanks,
> > 
> > Could put a flag word in superblock_operations.  Filesystems which
> > support punching (or other features) can enable it there.
> 
> No, it couldn't be in super_operations.  It may vary on a per-inode
> basis for some file systems, such as ext4 (depending on whether the
> inode is extent-mapped or indirect-block mapped).
> 
> So at least for ext4 we'd need to call into fallocate() function
> anyway, once we add support.  I suppose if other file systems really
> want it, we could add a flag to the super block ops structure, so they
> don't have do the "do we support the punch" operation.  I can go
> either way on that; although if we think the majority of file systems
> are going support punch in the long-term, then it might not be worth
> it to add such a flag.
>

Yeah thats alot of extra code just for one part of fallocate.  Calling into
->fallocate is perfectly reasonable, especially since ext4 works the way it
does, I'm going to leave things as they are.  Thanks,

Josef 
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